CODES

ADOPTS WITH AMENDMENTS:

International Fuel Gas Code 2009 (IFGC 2009)

Chapter 1 Scope and Administration

Chapter 2 Definitions

Chapter 3 General Regulations

Chapter 4 Gas Piping Installations

Chapter 5 Chimneys and Vents

Chapter 6 SPECIFIC APPLIANCES, Fireplaces and Solid Fuel-Burning Equipment

Chapter 7 Gaseous Hydrogen Systems

Chapter 8 Referenced Standards

Appendix A (IFGS) SIZING AND CAPACITIES OF GAS PIPING

Appendix B (IFGS) SIZING OF VENTING SYSTEMS SERVING APPLIANCES EQUIPPED WITH DRAFT HOODS, CATEGORY I APPLIANCES, AND APPLIANCES LISTED FOR USE WITH TYPE B VENTS

Appendix C (IFGS) EXIT TERMINALS OF MECHANICAL DRAFT AND DIRECT-VENT VENTING SYSTEMS

Appendix D (IFGS) RECOMMENDED PROCEDURE FOR SAFETY INSPECTION OF AN EXISTING APPLIANCE INSTALLATION

501.1 Scope

STATE AMENDMENT
This chapter, and Appendices B and C shall govern the installation, maintenance, repair and approval of factory-built chimneys, chimney liners, vents and connectors and the utilization of masonry chimneys serving gas-fired appliances. The requirements for the installation, maintenance, repair and approval of factory-built chimneys, chimney liners, vents and connectors serving appliances burning fuels other than fuel gas shall be regulated by the International Mechanical Code. The construction, repair, maintenance and approval of masonry chimneys shall be regulated by the International Building Code.
Every appliance shall discharge the products of combustion to the outdoors, except for appliances exempted by Section 501.8.
Masonry chimneys shall be constructed in accordance with Section 503.5.3 and the International Building Code.
Chimneys and vents shall be sized in accordance with Sections 503 and 504.
Abandoned inlet openings in chimneys and vents shall be closed by an approved method.
Where an appliance equipped with a mechanical forced draft system creates a positive pressure in the venting system, the venting system shall be designed for positive pressure applications.
Connection of appliances to chimney flues serving fireplaces shall be in accordance with Sections 501.7.1 through 501.7.3.
A noncombustible seal shall be provided below the point of connection to prevent entry of room air into the flue. Means shall be provided for access to the flue for inspection and cleaning.
An appliance shall not be connected to a flue serving a factory-built fireplace unless the appliance is specifically listed for such installation. The connection shall be made in accordance with the appliance manufacturer’s installation instructions.
A connector shall extend from the appliance to the flue serving a masonry fireplace such that the flue gases are exhausted directly into the flue. The connector shall be accessible or removable for inspection and cleaning of both the connector and the flue. Listed direct connection devices shall be installed in accordance with their listing.

The following appliances shall not be required to be vented.

1. Ranges.

2. Built-in domestic cooking units listed and marked for optional venting.

3. Hot plates and laundry stoves.

4. Type 1 clothes dryers (Type 1 clothes dryers shall be exhausted in accordance with the requirements of Section 614).

5. A single booster-type automatic instantaneous water heater, where designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the heater is installed in a commercial kitchen having a mechanical exhaust system. Where installed in this manner, the draft hood, if required, shall be in place and unaltered and the draft hood outlet shall be not less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from any surface other than the heater.

6. Refrigerators.

7. Counter appliances.

8. Room heaters listed for unvented use.

9. Direct-fired makeup air heaters.

10. Other appliances listed for unvented use and not provided with flue collars.

11. Specialized appliances of limited input such as laboratory burners and gas lights.

Where the appliances listed in Items 5 through 11 above are installed so that the aggregate input rating exceeds 20 British thermal units (Btu) per hour per cubic feet (207 watts per m3) of volume of the room or space in which such appliances are installed, one or more shall be provided with venting systems or other approved means for conveying the vent gases to the outdoor atmosphere so that the aggregate input rating of the remaining unvented appliances does not exceed 20 Btu per hour per cubic foot (207 watts per m3). Where the room or space in which the appliance is installed is directly connected to another room or space by a doorway, archway or other opening of comparable size that cannot be closed, the volume of such adjacent room or space shall be permitted to be included in the calculations.

Connectors shall connect to a masonry chimney flue at a point not less than 12 inches (305 mm) above the lowest portion of the interior of the chimney flue.
Appliance connections to a chimney or vent equipped with a power exhauster shall be made on the inlet side of the exhauster. Joints on the positive pressure side of the exhauster shall be sealed to prevent flue-gas leakage as specified by the manufacturer’s installation instructions for the exhauster.
Masonry chimneys utilized to vent appliances shall be located, constructed and sized as specified in the manufacturer’s installation instructions for the appliances being vented and Section 503.

Flue lining systems for use with residential-type and low-heat appliances shall be limited to the following:

1. Clay flue lining complying with the requirements of ASTM C 315 or equivalent. Clay flue lining shall be installed in accordance with the International Building Code.

2. Listed chimney lining systems complying with UL 1777.

3. Other approved materials that will resist, without cracking, softening or corrosion, flue gases and condensate at temperatures up to 1,800°F (982°C).

Flue lining systems for use with Category I appliances shall be limited to the following:

1. Flue lining systems complying with Section 501.12.

2. Chimney lining systems listed and labeled for use with gas appliances with draft hoods and other Category I gas appliances listed and labeled for use with Type B vents.

The design, sizing and installation of vents for Category II, III and IV appliances shall be in accordance with the appliance manufacturer’s installation instructions.
Where an appliance is permanently disconnected from an existing chimney or vent, or where an appliance is connected to an existing chimney or vent during the process of a new installation, the chimney or vent shall comply with Sections 501.15.1 through 501.15.4.
The chimney or vent shall be resized as necessary to control flue gas condensation in the interior of the chimney or vent and to provide the appliance or appliances served with the required draft. For Category I appliances, the resizing shall be in accordance with Section 502.
The flue gas passageway shall be free of obstructions and combustible deposits and shall be cleaned if previously used for venting a solid or liquid fuel-burning appliance or fireplace. The flue liner, chimney inner wall or vent inner wall shall be continuous and shall be free of cracks, gaps, perforations or other damage or deterioration which would allow the escape of combustion products, including gases, moisture and creosote.
Masonry chimney flues shall be provided with a cleanout opening having a minimum height of 6 inches (152 mm). The upper edge of the opening shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The cleanout shall be provided with a tight-fitting, noncombustible cover.

Chimneys and vents shall have airspace clearance to combustibles in accordance with the International Building Code and the chimney or vent manufacturer’s installation instructions.

Exception: Masonry chimneys without the required airspace clearances shall be permitted to be used if lined or relined with a chimney lining system listed for use in chimneys with reduced clearances in accordance with UL 1777. The chimney clearance shall be not less than permitted by the terms of the chimney liner listing and the manufacturer’s instructions.

Noncombustible fireblocking shall be provided in accordance with the International Building Code.
All vents, except as provided in Section 503.7, shall be listed and labeled. Type B and BW vents shall be tested in accordance with UL 441. Type L vents shall be tested in accordance with UL 641. Vents for Category II and III appliances shall be tested in accordance with UL 1738. Plastic vents for Category IV appliances shall not be required to be listed and labeled where such vents are as specified by the appliance manufacturer and are installed in accordance with the appliance manufacturer’s installation instructions.
Connectors shall be used to connect appliances to the vertical chimney or vent, except where the chimney or vent is attached directly to the appliance. Vent connector size, material, construction and installation shall be in accordance with Section 503.
The application of vents shall be in accordance with Table 503.4.
Where vents pass through insulated assemblies, an insulation shield constructed of steel having a minimum thickness of 0.0187 inch (0.4712 mm) (No. 26 gage) shall be installed to provide clearance between the vent and the insulation material. The clearance shall not be less than the clearance to combustibles specified by the vent manufacturer’s installation instructions. Where vents pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed vent system shall be installed in accordance with the manufacturer’s installation instructions.
Vent systems shall be sized, installed and terminated in accordance with the vent and appliance manufacturer’s installation instructions and Section 503.
All portions of vents shall be adequately supported for the design and weight of the materials employed.
In concealed locations, where a vent is installed through holes or notches in studs, joists, rafters or similar members less than 11/2 inches (38 mm) from the nearest edge of the member, the vent shall be protected by shield plates. Protective steel shield plates having a minimum thickness of 0.0575 inch (1.463 mm) (No. 16 gage) shall cover the area of the vent where the member is notched or bored and shall extend a minimum of 4 inches (102 mm) above sole plates, below top plates and to each side of a stud, joist or rafter.
This section recognizes that the choice of venting materials and the methods of installation of venting systems are dependent on the operating characteristics of the appliance being vented. The operating characteristics of vented appliances can be categorized with respect to: (1) positive or negative pressure within the venting system; and (2) whether or not the appliance generates flue or vent gases that might condense in the venting system. See Section 202 for the definitions of these vented appliance categories.
Except as permitted in Sections 503.2.1 through 503.2.4 and 501.8, all appliances shall be connected to venting systems.
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications (see Section 503.3.4) and to vent industrial appliances, such as where the process itself requires fume disposal.
Where located in a large and well-ventilated space, industrial appliances shall be permitted to be operated by discharging the flue gases directly into the space.
Listed direct-vent appliances shall be installed in accordance with the manufacturer’s instructions and Section 503.8, Item 3.
Appliances incorporating integral venting means shall be considered properly vented where installed in accordance with the manufacturer’s instructions and Section 503.8, Items 1 and 2.
A venting system shall be designed and constructed so as to develop a positive flow adequate to convey flue or vent gases to the outdoors.
A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer’s instructions.
Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Sections 503.4 through 503.16.

Mechanical draft systems shall comply with the following:

1. Mechanical draft systems shall be listed and shall be installed in accordance with the manufacturer’s installation instructions for both the appliance and the mechanical draft system.

2. Appliances, except incinerators, requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design.

3. Forced draft systems and all portions of induced draft systems under positive pressure during operation shall be designed and installed so as to prevent leakage of flue or vent gases into a building.

4. Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure.

5. Where a mechanical draft system is employed, provisions shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance.

6. The exit terminals of mechanical draft systems shall be not less than 7 feet (2134 mm) above finished ground level where located adjacent to public walkways and shall be located as specified in Section 503.8, Items 1 and 2.

Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications. Where automatically operated appliances, other than commercial cooking appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners only when the damper is open to a position to properly vent the appliance and when the power means of exhaust is in operation.

TABLE 503.4
TYPE OF VENTING SYSTEM TO BE USED

APPLIANCES

TYPE OF VENTING SYSTEM

Listed Category I appliances

Listed appliances equipped with draft hood

Appliances listed for use with Type B gas vent

Type B gas vent (Section 503.6)

Chimney (Section 503.5)

Single-wall metal pipe (Section 503.7)

Listed chimney lining system for gas venting (Section 503.5.3)

Special gas vent listed for these appliances (Section 503.4.2)

Listed vented wall furnaces

Type B-W gas vent (Sections 503.6, 608)

Category II appliances

As specified or furnished by manufacturers of listed appliances (Sections 503.4.1, 503.4.2)

Category III appliances

As specified or furnished by manufacturers of listed appliances (Sections 503.4.1, 503.4.2)

Category IV appliances

As specified or furnished by manufacturers of listed appliances (Sections 503.4.1, 503.4.2)

Incinerators, indoors

Chimney (Section 503.5)

Incinerators, outdoors

Single-wall metal pipe (Sections 503.7, 503.7.6)

Appliances that can be converted for use with solid fuel

Chimney (Section 503.5)

Unlisted combination gas and oil-burning appliances

Chimney (Section 503.5)

Listed combination gas and oil-burning appliances

Type L vent (Section 503.6) or chimney (Section 503.5)

Combination gas and solid fuel-burning appliances

Chimney (Section 503.5)

Appliances listed for use with chimneys only

Chimney (Section 503.5)

Unlisted appliances

Chimney (Section 503.5)

Decorative appliances in vented fireplaces

Chimney

Gas-fired toilets

Single-wall metal pipe (Section 626)

Direct-vent appliances

See Section 503.2.3

Appliances with integral vent

See Section 503.2.4

Venting systems shall not extend into or pass through any fabricated air duct or furnace plenum.

Where a venting system passes through an above-ceiling air-handling space or other nonducted portion of an air-handling system, the venting system shall conform to one of the following requirements:

1. The venting system shall be a listed special gas vent; other venting system serving a Category III or Category IV appliance; or other positive pressure vent, with joints sealed in accordance with the appliance or vent manufacturer’s instructions.

2. The venting system shall be installed such that fittings and joints between sections are not installed in the above-ceiling space.

3. The venting system shall be installed in a conduit or enclosure with sealed joints separating the interior of the conduit or enclosure from the ceiling space.

The type of venting system to be used shall be in accordance with Table 503.4.
Plastic piping used for venting appliances listed for use with such venting materials shall be approved.
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions. Where a primer is required, it shall be of a contrasting color.
Special gas vent shall be listed and installed in accordance with the special gas vent manufacturer’s installation instructions.
Masonry, metal and factory-built chimneys shall comply with Sections 503.5.1 through 503.5.10.
Factory-built chimneys shall be installed in accordance with the manufacturer’s installation instructions. Factory-built chimneys used to vent appliances that operate at a positive vent pressure shall be listed for such application.
Metal chimneys shall be built and installed in accordance with NFPA 211.

Masonry chimneys shall be built and installed in accordance with NFPA 211 and shall be lined with approved clay flue lining, a listed chimney lining system or other approved material that will resist corrosion, erosion, softening or cracking from vent gases at temperatures up to 1,800°F (982°C).

Exception: Masonry chimney flues serving listed gas appliances with draft hoods, Category I appliances and other gas appliances listed for use with Type B vents shall be permitted to be lined with a chimney lining system specifically listed for use only with such appliances. The liner shall be installed in accordance with the liner manufacturer’s installation instructions. A permanent identifying label shall be attached at the point where the connection is to be made to the liner. The label shall read: “This chimney liner is for appliances that burn gas only. Do not connect to solid or liquid fuel-burning appliances or incinerators.”

For installation of gas vents in existing masonry chimneys, see Section 503.6.3.

Chimneys for residential- type or low-heat appliances shall extend at least 3 feet (914 mm) above the highest point where they pass through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm) (see Figure 503.5.4). Chimneys for medium-heat appliances shall extend at least 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). Chimneys shall extend at least 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar. Decorative shrouds shall not be installed at the termination of factory-built chimneys except where such shrouds are listed and labeled for use with the specific factory-built chimney system and are installed in accordance with the manufacturer’s installation instructions.

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

FIGURE 503.5.4
TYPICAL TERMINATION LOCATIONS FOR
CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING
RESIDENTIAL-TYPE AND LOW-HEAT EQUIPMENT

The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances and other appliances listed for use with Type B vents shall be determined in accordance with one of the following methods:

1. The provisions of Section 504.

2. For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet, nor greater than seven times the draft hood outlet area.

3. For sizing a chimney venting system connected to two appliances with draft hoods, the effective area of the chimney flue shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smallest draft hood outlet area.

4. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.

5. Other approved engineering methods.

Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway shall be examined to ascertain that it is clear and free of obstructions and it shall be cleaned if previously used for venting solid or liquid fuel-burning appliances or fireplaces.

Chimneys shall be lined in accordance with NFPA 211.

Exception: Where an existing chimney complies with Sections 503.5.6 through 503.5.6.3 and its sizing is in accordance with Section 503.5.5, its continued use shall be allowed where the appliance vented by such chimney is replaced by an appliance of similar type, input rating and efficiency.

Cleanouts shall be examined to determine if they will remain tightly closed when not in use.
Where inspection reveals that an existing chimney is not safe for the intended application, it shall be repaired, rebuilt, lined, relined or replaced with a vent or chimney to conform to NFPA 211 and it shall be suitable for the appliances to be vented.
Chimneys serving appliances burning other fuels shall comply with Sections 503.5.7.1 through 503.5.7.4.
An appliance shall not be connected to a chimney flue serving a separate appliance designed to burn solid fuel.
Where one chimney flue serves gas appliances and liquid fuel-burning appliances, the appliances shall be connected through separate openings or shall be connected through a single opening where joined by a suitable fitting located as close as practical to the chimney. Where two or more openings are provided into one chimney flue, they shall be at different levels. Where the appliances are automatically controlled, they shall be equipped with safety shutoff devices.
A combination gas- and solid fuel-burning appliance shall be permitted to be connected to a single chimney flue where equipped with a manual reset device to shut off gas to the main burner in the event of sustained backdraft or flue gas spillage. The chimney flue shall be sized to properly vent the appliance.
A listed combination gas- and oil fuel-burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance.
All portions of chimneys shall be supported for the design and weight of the materials employed. Factory-built chimneys shall be supported and spaced in accordance with the manufacturer’s installation instructions.
Where a chimney that formerly carried flue products from liquid or solid fuel-burning appliances is used with an appliance using fuel gas, an accessible cleanout shall be provided. The cleanout shall have a tight-fitting cover and shall be installed so its upper edge is at least 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening.

The remaining space surrounding a chimney liner, gas vent, special gas vent or plastic piping installed within a masonry chimney flue shall not be used to vent another appliance. The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer’s instructions shall not be prohibited.

The remaining space surrounding a chimney liner, gas vent, special gas vent or plastic piping installed within a masonry, metal or factory-built chimney shall not be used to supply combustion air. Such space shall not be prohibited from supplying combustion air to direct-vent appliances designed for installation in a solid fuel-burning fireplace and installed in accordance with the manufacturer’s installation instructions.

Gas vents shall comply with Sections 503.6.1 through 503.6.13 (see Section 202, Definitions).
Gas vents shall be installed in accordance with the manufacturer’s installation instructions.
A Type B-W gas vent shall have a listed capacity not less than that of the listed vented wall furnace to which it is connected.
Gas vents installed within masonry chimneys shall be installed in accordance with the manufacturer’s installation instructions. Gas vents installed within masonry chimneys shall be identified with a permanent label installed at the point where the vent enters the chimney. The label shall contain the following language: “This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.”

A gas vent shall terminate in accordance with one of the following:

1. Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 503.6.4.

2. Gas vents that are over 12 inches (305 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.

3. As provided for industrial appliances in Section 503.2.2.

4. As provided for direct-vent systems in Section 503.2.3.

5. As provided for appliances with integral vents in Section 503.2.4.

6. As provided for mechanical draft systems in Section 503.3.3.

7. As provided for ventilating hoods and exhaust systems in Section 503.3.4.

ROOF SLOPE

H (min) ft

Flat to 6/12

1.0

Over 6/12 to 7/12

1.25

Over 7/12 to 8/12

1.5

Over 8/12 to 9/12

2.0

Over 9/12 to 10/12

2.5

Over 10/12 to 11/12

3.25

Over 11/12 to 12/12

4.0

Over 12/12 to 14/12

5.0

Over 14/12 to 16/12

6.0

Over 16/12 to 18/12

7.0

Over 18/12 to 20/12

7.5

Over 20/12 to 21/12

8.0

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

FIGURE 503.6.4
TERMINATION LOCATIONS FOR GAS VENTS WITH
LISTED CAPS 12 INCHES OR LESS IN SIZE AT LEAST 8 FEET FROM A VERTICAL WALL

Decorative shrouds shall not be installed at the termination of gas vents except where such shrouds are listed for use with the specific gas venting system and are installed in accordance with manufacturer’s installation instructions.
A Type B or L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.
Gas vents shall extend through the roof flashing, roof jack or roof thimble and terminate with a listed cap or listed roof assembly.
Gas vents shall terminate not less than 3 feet (914 mm) above any forced air inlet located within 10 feet (3048 mm).
A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Sections 503.2.3 and 503.3.3.
Venting systems shall be sized and constructed in accordance with Section 504 or other approved engineering methods and the gas vent and appliance manufacturer’s installation instructions.

The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following methods:

1. The provisions of Section 504.

2. For sizing an individual gas vent for a single, draft-hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet, nor greater than seven times the draft hood outlet area.

3. For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smaller draft hood outlet area.

4. Approved engineering practices.

Type B and L vents sized in accordance with Item 2 or 3 of Section 503.6.9.1 shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60-degree (1.04 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall be not greater than 75 percent of the vertical height of the vent.
The sizing of gas vents for Category II, III and IV appliances shall be in accordance with the appliance manufacturer’s instructions.
Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
A common gas vent shall be permitted in multistory installations to vent Category I appliances located on more than one floor level, provided that the venting system is designed and installed in accordance with approved engineering methods. For the purpose of this section, crawl spaces, basements and attics shall be considered as floor levels.

All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation and dilution air that is not supplied from an occupiable space (see Figure 503.6.10.1).

FIGURE 503.6.10.1
PLAN VIEW OF PRACTICAL SEPARATION METHOD
FOR MULTISTORY GAS VENTING

The size of the connectors and common segments of multistory venting systems for appliances listed for use with Type B double-wall gas vents shall be in accordance with Table 504.3(1), provided that:

1. The available total height (H) for each segment of a multistory venting system is the vertical distance between the level of the highest draft hood outlet or flue collar on that floor and the centerline of the next highest interconnection tee (see Figure B-13).

2. The size of the connector for a segment is determined from the appliance input rating and available connector rise, and shall not be smaller than the draft hood outlet or flue collar size.

3. The size of the common vertical segment, and of the interconnection tee at the base of that segment, shall be based on the total appliance input rating entering that segment and its available total height.

Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions.

In those localities where solid and liquid fuels are used extensively, gas vents shall be permanently identified by a label attached to the wall or ceiling at a point where the vent connector enters the gas vent. The determination of where such localities exist shall be made by the code official. The label shall read:

“This gas vent is for appliances that burn gas. Do not connect to solid or liquid fuel-burning appliances or incinerators.”

Screws, rivets and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from an appliance draft hood outlet, a flue collar or a single-wall metal connector to a double-wall vent.
Single-wall metal pipe vents shall comply with Sections 503.7.1 through 503.7.13.
Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 inch (0.7 mm) thick, or other approved, noncombustible, corrosion-resistant material.
Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99-percent winter design temperature is below 32°F (0°C).
Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm) (see Figure 503.5.4). An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe (see also Section 503.7.9, Item 3).
Single-wall metal pipe shall be used only for runs directly from the space in which the appliance is located through the roof or exterior wall to the outdoor atmosphere.
A pipe passing through a roof shall extend without interruption through the roof flashing, roof jack or roof thimble. Where a single-wall metal pipe passes through a roof constructed of combustible material, a noncombustible, nonventilating thimble shall be used at the point of passage. The thimble shall extend at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section 503.7.7.
Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space or floor. The installation of a single-wall metal pipe through an exterior combustible wall shall comply with Section 503.7.7. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have suitable clearances maintained.

A single-wall metal pipe shall not pass through a combustible exterior wall unless guarded at the point of passage by a ventilated metal thimble not smaller than the following:

1. For listed appliances equipped with draft hoods and appliances listed for use with Type B gas vents, the thimble shall be not less than 4 inches (102 mm) larger in diameter than the metal pipe. Where there is a run of not less than 6 feet (1829 mm) of metal pipe in the open between the draft hood outlet and the thimble, the thimble shall be permitted to be not less than 2 inches (51 mm) larger in diameter than the metal pipe.

2. For unlisted appliances having draft hoods, the thimble shall be not less than 6 inches (152 mm) larger in diameter than the metal pipe.

3. For residential and low-heat appliances, the thimble shall be not less than 12 inches (305 mm) larger in diameter than the metal pipe.

Exception: In lieu of thimble protection, all combustible material in the wall shall be removed a sufficient distance from the metal pipe to provide the specified clearance from such metal pipe to combustible material. Any material used to close up such opening shall be noncombustible.

Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 503.10.5. The clearance from single-wall metal pipe to combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 308.2.

A venting system constructed of single-wall metal pipe shall be sized in accordance with one of the following methods and the appliance manufacturer’s instructions:

1. For a draft-hood-equipped appliance, in accordance with Section 504.

2. For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall be not less than the area of the appliance flue collar or draft hood outlet, whichever is smaller. The vent area shall not be greater than seven times the draft hood outlet area.

3. Other approved engineering methods.

Any shaped single-wall metal pipe shall be permitted to be used, provided that its equivalent effective area is equal to the effective area of the round pipe for which it is substituted, and provided that the minimum internal dimension of the pipe is not less than 2 inches (51 mm).
The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached.
All portions of single-wall metal pipe shall be supported for the design and weight of the material employed.
Single-wall metal pipe shall comply with the marking provisions of Section 503.6.12.

The location of venting system terminations shall comply with the following (see Appendix C):

1. A mechanical draft venting system shall terminate at least 3 feet (914 mm) above any forced-air inlet located within 10 feet (3048 mm).

Exceptions:

1. This provision shall not apply to the combustion air intake of a direct-vent appliance.

2. This provision shall not apply to the separation of the integral outdoor air inlet and flue gas discharge of listed outdoor appliances.

2. A mechanical draft venting system, excluding direct- vent appliances, shall terminate at least 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from, or 1 foot (305 mm) above any door, operable window or gravity air inlet into any building. The bottom of the vent terminal shall be located at least 12 inches (305 mm) above finished ground level.

3. The vent terminal of a direct-vent appliance with an input of 10,000 Btu per hour (3 kW) or less shall be located at least 6 inches (152 mm) from any air opening into a building, and such an appliance with an input over 10,000 Btu per hour (3 kW) but not over 50,000 Btu per hour (14.7 kW) shall be installed with a 9-inch (230 mm) vent termination clearance, and an appliance with an input over 50,000 Btu/h (14.7 kW) shall have at least a 12-inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located at least 12 inches (305 mm) above finished ground level.

4. Through-the-wall vents for Category II and IV appliances and noncategorized condensing appliances shall not terminate over public walkways or over an area where condensate or vapor could create a nuisance or hazard or could be detrimental to the operation of regulators, relief valves or other equipment. Where local experience indicates that condensate is a problem with Category I and III appliances, this provision shall also apply. Drains for condensate shall be installed in accordance with the manufacturer’s installation instructions.

Provisions shall be made to collect and dispose of condensate from venting systems serving Category II and IV appliances and noncategorized condensing appliances in accordance with Section 503.8, Item 4. Where local experience indicates that condensation is a problem, provision shall be made to drain off and dispose of condensate from venting systems serving Category I and III appliances in accordance with Section 503.8, Item 4.
Vent connectors for Category I appliances shall comply with Sections 503.10.1 through 503.10.15.
A vent connector shall be used to connect an appliance to a gas vent, chimney or single-wall metal pipe, except where the gas vent, chimney or single-wall metal pipe is directly connected to the appliance.
Vent connectors shall be constructed in accordance with Sections 503.10.2.1 through 503.10.2.5.
A vent connector shall be made of noncombustible corrosion-resistant material capable of withstanding the vent gas temperature produced by the appliance and of sufficient thickness to withstand physical damage.

Where the vent connector used for an appliance having a draft hood or a Category I appliance is located in or passes through attics, crawl spaces or other unconditioned spaces, that portion of the vent connector shall be listed Type B, Type L or listed vent material having equivalent insulation properties.

Exception: Single-wall metal pipe located within the exterior walls of the building in areas having a local 99-percent winter design temperature of 5°F (-15°C) or higher shall be permitted to be used in unconditioned spaces other than attics and crawl spaces.

Where vent connectors for residential-type appliances are not installed in attics or other unconditioned spaces, connectors for listed appliances having draft hoods, appliances having draft hoods and equipped with listed conversion burners and Category I appliances shall be one of the following:

1. Type B or L vent material;

2. Galvanized sheet steel not less than 0.018 inch (0.46 mm) thick;

3. Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 inch (0.69 mm) thick;

4. Stainless steel sheet not less than 0.012 inch (0.31 mm) thick;

5. Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Item 2, 3 or 4 above; or

6. A listed vent connector.

Vent connectors shall not be covered with insulation.

Exception: Listed insulated vent connectors shall be installed in accordance with the manufacturer’s installation instructions.

A vent connector for a nonresidential, low-heat appliance shall be a factory-built chimney section or steel pipe having resistance to heat and corrosion equivalent to that for the appropriate galvanized pipe as specified in Table 503.10.2.4. Factory-built chimney sections shall be joined together in accordance with the chimney manufacturer’s instructions.

TABLE 503.10.2.4
MINIMUM THICKNESS FOR GALVANIZED STEEL VENT
CONNECTORS FOR LOW-HEAT APPLIANCES

DIAMETER OF CONNECTOR (inches)

MINIMUM THICKNESS
(inch)

Less than 6

0.019

6 to less than 10

0.023

10 to 12 inclusive

0.029

14 to 16 inclusive

0.034

Over 16

0.056

For SI: 1 inch = 25.4 mm.

Vent connectors for medium-heat appliances and commercial and industrial incinerators shall be constructed of factory-built medium-heat chimney sections or steel of a thickness not less than that specified in Table 503.10.2.5 and shall comply with the following:

1. A steel vent connector for an appliance with a vent gas temperature in excess of 1,000°F (538°C) measured at the entrance to the connector shall be lined with medium-duty fire brick (ASTM C 64, Type F), or the equivalent.

2. The lining shall be at least 21/2 inches (64 mm) thick for a vent connector having a diameter or greatest cross-sectional dimension of 18 inches (457 mm) or less.

3. The lining shall be at least 41/2 inches (114 mm) thick laid on the 41/2-inch (114 mm) bed for a vent connector having a diameter or greatest cross-sectional dimension greater than 18 inches (457 mm).

4. Factory-built chimney sections, if employed, shall be joined together in accordance with the chimney manufacturer’s instructions.

TABLE 503.10.2.5
MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR
MEDIUM-HEAT APPLIANCES AND COMMERCIAL AND
INDUSTRIAL INCINERATORS VENT CONNECTOR SIZE

DIAMETER
(inches)

AREA
(square inches)

MINIMUM THICKNESS (inch)

Up to 14

Up to 154

0.053

Over 14 to 16

154 to 201

0.067

Over 16 to 18

201 to 254

0.093

Over 18

Larger than 254

0.123

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.

Vent connectors shall be sized in accordance with Sections 503.10.3.1 through 503.10.3.5.
A vent connector for an appliance with a single draft hood or for a Category I fan-assisted combustion system appliance shall be sized and installed in accordance with Section 504 or other approved engineering methods.
For a single appliance having more than one draft hood outlet or flue collar, the manifold shall be constructed according to the instructions of the appliance manufacturer. Where there are no instructions, the manifold shall be designed and constructed in accordance with approved engineering practices. As an alternate method, the effective area of the manifold shall equal the combined area of the flue collars or draft hood outlets and the vent connectors shall have a minimum 1-foot (305 mm) rise.

Where two or more appliances are connected to a common vent or chimney, each vent connector shall be sized in accordance with Section 504 or other approved engineering methods.

As an alternative method applicable only when all of the appliances are draft hood equipped, each vent connector shall have an effective area not less than the area of the draft hood outlet of the appliance to which it is connected.

Where two or more appliances are vented through a common vent connector or vent manifold, the common vent connector or vent manifold shall be located at the highest level consistent with available headroom and the required clearance to combustible materials and shall be sized in accordance with Section 504 or other approved engineering methods.

As an alternate method applicable only where there are two draft hood-equipped appliances, the effective area of the common vent connector or vent manifold and all junction fittings shall be not less than the area of the larger vent connector plus 50 percent of the area of the smaller flue collar outlet.

Where the size of a vent connector is increased to overcome installation limitations and obtain connector capacity equal to the appliance input, the size increase shall be made at the appliance draft hood outlet.
Where two or more vent connectors enter a common gas vent, chimney flue or single-wall metal pipe, the smaller connector shall enter at the highest level consistent with the available headroom or clearance to combustible material. Vent connectors serving Category I appliances shall not be connected to any portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or IV appliances.
Where two or more openings are provided into one chimney flue or vent, the openings shall be at different levels, or the connectors shall be attached to the vertical portion of the chimney or vent at an angle of 45 degrees (0.79 rad) or less relative to the vertical.

Minimum clearances from vent connectors to combustible material shall be in accordance with Table 503.10.5.

Exception: The clearance between a vent connector and combustible material shall be permitted to be reduced where the combustible material is protected as specified for vent connectors in Table 308.2.

TABLE 503.10.5a
CLEARANCES FOR CONNECTORS

APPLIANCE

MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL

Listed Type B gas
vent material

Listed Type L
vent material

Single-wall
metal pipe

Factory-built
chimney sections

Listed appliances with draft hoods and appliances listed for use with Type B gas vents

As listed

As listed

6 inches

As listed

Residential boilers and furnaces with listed gas conversion burner and with draft hood

6 inches

6 inches

9 inches

As listed

Residential appliances listed for use with Type L vents

Not permitted

As listed

9 inches

As listed

Listed gas-fired toilets

Not permitted

As listed

As listed

As listed

Unlisted residential appliances with draft hood

Not permitted

6 inches

9 inches

As listed

Residential and low-heat appliances other than above

Not permitted

9 inches

18 inches

As listed

Medium-heat appliances

Not permitted

Not permitted

36 inches

As listed

For SI: 1 inch = 25.4 mm.

a. These clearances shall apply unless the manufacturer’s installation instructions for a listed appliance or connector specify different clearances, in which case the listed clearances shall apply.

A vent connector shall be installed so as to avoid turns or other construction features that create excessive resistance to flow of vent gases.

Joints between sections of connector piping and connections to flue collars and draft hood outlets shall be fastened by one of the following methods:

1. Sheet metal screws.

2. Vent connectors of listed vent material assembled and connected to flue collars or draft hood outlets in accordance with the manufacturers’ instructions.

3. Other approved means.

A vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney at least 1/4 inch per foot (21 mm/m).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with the appliance and draft system manufacturers’ instructions.

A vent connector shall be as short as practical and the appliance located as close as practical to the chimney or vent. The maximum horizontal length of a single-wall connector shall be 75 percent of the height of the chimney or vent except for engineered systems. The maximum horizontal length of a Type B double-wall connector shall be 100 percent of the height of the chimney or vent except for engineered systems.
A vent connector shall be supported for the design and weight of the material employed to maintain clearances and prevent physical damage and separation of joints.
Where entering a flue in a masonry or metal chimney, the vent connector shall be installed above the extreme bottom to avoid stoppage. Where a thimble or slip joint is used to facilitate removal of the connector, the connector shall be firmly attached to or inserted into the thimble or slip joint to prevent the connector from falling out. Means shall be employed to prevent the connector from entering so far as to restrict the space between its end and the opposite wall of the chimney flue (see Section 501.9).
The entire length of a vent connector shall be provided with ready access for inspection, cleaning and replacement.
A vent connector shall not be connected to a chimney flue serving a fireplace unless the fireplace flue opening is permanently sealed.
Single-wall metal pipe connectors shall not pass through any wall, floor or ceiling except as permitted by Section 503.7.4.
Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material.
Vent connectors for Category II, III and IV appliances shall be as specified for the venting systems in accordance with Section 503.4.
The installation of draft hoods and draft controls shall comply with Sections 503.12.1 through 503.12.7.

Vented appliances shall be installed with draft hoods.

Exception: Dual oven-type combination ranges; incinerators; direct-vent appliances; fan-assisted combustion system appliances; appliances requiring chimney draft for operation; single firebox boilers equipped with conversion burners with inputs greater than 400,000 Btu per hour (117 kW); appliances equipped with blast, power or pressure burners that are not listed for use with draft hoods; and appliances designed for forced venting.

A draft hood supplied with or forming a part of a listed vented appliance shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer.
If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, shall be of a listed or approved type and, in the absence of other instructions, shall be of the same size as the appliance flue collar. Where a draft hood is required with a conversion burner, it shall be of a listed or approved type.
Where it is determined that a draft hood of special design is needed or preferable for a particular installation, the installation shall be in accordance with the recommendations of the appliance manufacturer and shall be approved.
Where a draft control device is part of the appliance or is supplied by the appliance manufacturer, it shall be installed in accordance with the manufacturer’s instructions. In the absence of manufacturer’s instructions, the device shall be attached to the flue collar of the appliance or as near to the appliance as practical.
Appliances (except incinerators) requiring a controlled chimney draft shall be permitted to be equipped with a listed double-acting barometric-draft regulator installed and adjusted in accordance with the manufacturer’s instructions.
Draft hoods and barometric draft regulators shall be installed in the same room or enclosure as the appliance in such a manner as to prevent any difference in pressure between the hood or regulator and the combustion air supply.
Draft hoods and draft regulators shall be installed in the position for which they were designed with reference to the horizontal and vertical planes and shall be located so that the relief opening is not obstructed by any part of the appliance or adjacent construction. The appliance and its draft hood shall be located so that the relief opening is accessible for checking vent operation.
A draft hood shall be located so its relief opening is not less than 6 inches (152 mm) from any surface except that of the appliance it serves and the venting system to which the draft hood is connected. Where a greater or lesser clearance is indicated on the appliance label, the clearance shall be not less than that specified on the label. Such clearances shall not be reduced.
A manually operated damper shall not be placed in the vent connector for any appliance. Fixed baffles shall not be classified as manually operated dampers.
An automatically operated vent damper shall be of a listed type.

Devices that retard the flow of vent gases shall not be installed in a vent connector, chimney or vent. The following shall not be considered as obstructions:

1. Draft regulators and safety controls specifically listed for installation in venting systems and installed in accordance with the manufacturer’s installation instructions.

2. Approved draft regulators and safety controls that are designed and installed in accordance with approved engineering methods.

3. Listed heat reclaimers and automatically operated vent dampers installed in accordance with the manufacturer’s installation instructions.

4. Approved economizers, heat reclaimers and recuperators installed in venting systems of appliances not required to be equipped with draft hoods, provided that the appliance manufacturer’s instructions cover the installation of such a device in the venting system and performance in accordance with Sections 503.3 and 503.3.1 is obtained.

5. Vent dampers serving listed appliances installed in accordance with Sections 504.2.1 and 504.3.1 or other approved engineering methods.

Where vents, including those for direct-vent appliances, penetrate outside walls of buildings, the annular spaces around such penetrations shall be permanently sealed using approved materials to prevent entry of combustion products into the building.

The following definitions apply to the tables in this section.

APPLIANCE CATEGORIZED VENT DIAMETER/ AREA. The minimum vent area/diameter permissible for Category I appliances to maintain a nonpositive vent static pressure when tested in accordance with nationally recognized standards.

FAN-ASSISTED COMBUSTION SYSTEM. An appliance equipped with an integral mechanical means to either draw or force products of combustion through the combustion chamber or heat exchanger.

FAN Min. The minimum input rating of a Category I fan-assisted appliance attached to a vent or connector.

FAN Max. The maximum input rating of a Category I fan-assisted appliance attached to a vent or connector.

NAT Max. The maximum input rating of a Category I draft-hood-equipped appliance attached to a vent or connector.

FAN + FAN. The maximum combined appliance input rating of two or more Category I fan-assisted appliances attached to the common vent.

FAN + NAT. The maximum combined appliance input rating of one or more Category I fan-assisted appliances and one or more Category I draft-hood-equipped appliances attached to the common vent.

NA. Vent configuration is not allowed due to potential for condensate formation or pressurization of the venting system, or not applicable due to physical or geometric restraints.

NAT + NAT. The maximum combined appliance input rating of two or more Category I draft-hood-equipped appliances attached to the common vent.

The application of Tables 504.2(1) through 504.2(6) shall be subject to the requirements of Sections 504.2.1 through 504.2.16.

TABLE 504.2(1)
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Connected directly to vent

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

3

4

5

6

7

8

9

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

0

0

78

46

0

152

86

0

251

141

0

375

205

0

524

285

0

698

370

0

897

470

2

13

51

36

18

97

67

27

157

105

32

232

157

44

321

217

53

425

285

63

543

370

4

21

49

34

30

94

64

39

153

103

50

227

153

66

316

211

79

419

279

93

536

362

6

25

46

32

36

91

61

47

149

100

59

223

149

78

310

205

93

413

273

110

530

354

8

0

0

84

50

0

165

94

0

276

155

0

415

235

0

583

320

0

780

415

0

1,006

537

2

12

57

40

16

109

75

25

178

120

28

263

180

42

365

247

50

483

322

60

619

418

5

23

53

38

32

103

71

42

171

115

53

255

173

70

356

237

83

473

313

99

607

407

8

28

49

35

39

98

66

51

164

109

64

247

165

84

347

227

99

463

303

117

596

396

10

0

0

88

53

0

175

100

0

295

166

0

447

255

0

631

345

0

847

450

0

1,096

585

2

12

61

42

17

118

81

23

194

129

26

289

195

40

402

273

48

533

355

57

684

457

5

23

57

40

32

113

77

41

187

124

52

280

188

68

392

263

81

522

346

95

671

446

10

30

51

36

41

104

70

54

176

115

67

267

175

88

376

245

104

504

330

122

651

427

15

0

0

94

58

0

191

112

0

327

187

0

502

285

0

716

390

0

970

525

0

1,263

682

2

11

69

48

15

136

93

20

226

150

22

339

225

38

475

316

45

633

414

53

815

544

5

22

65

45

30

130

87

39

219

142

49

330

217

64

463

300

76

620

403

90

800

529

10

29

59

41

40

121

82

51

206

135

64

315

208

84

445

288

99

600

386

116

777

507

15

35

53

37

48

112

76

61

195

128

76

301

198

98

429

275

115

580

373

134

755

491

20

0

0

97

61

0

202

119

0

349

202

0

540

307

0

776

430

0

1,057

575

0

1,384

752

2

10

75

51

14

149

100

18

250

166

20

377

249

33

531

346

41

711

470

50

917

612

5

21

71

48

29

143

96

38

242

160

47

367

241

62

519

337

73

697

460

86

902

599

10

28

64

44

38

133

89

50

229

150

62

351

228

81

499

321

95

675

443

112

877

576

15

34

58

40

46

124

84

59

217

142

73

337

217

94

481

308

111

654

427

129

853

557

20

48

52

35

55

116

78

69

206

134

84

322

206

107

464

295

125

634

410

145

830

537

(continued)

TABLE 504.2(1)
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Connected directly to vent

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

3

4

5

6

7

8

9

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

30

0

0

100

64

0

213

128

0

374

220

0

587

336

0

853

475

0

1,173

650

0

1,548

855

2

9

81

56

13

166

112

14

283

185

18

432

280

27

613

394

33

826

535

42

1,072

700

5

21

77

54

28

160

108

36

275

176

45

421

273

58

600

385

69

811

524

82

1,055

688

10

27

70

50

37

150

102

48

262

171

59

405

261

77

580

371

91

788

507

107

1,028

668

15

33

64

NA

44

141

96

57

249

163

70

389

249

90

560

357

105

765

490

124

1,002

648

20

56

58

NA

53

132

90

66

237

154

80

374

237

102

542

343

119

743

473

139

977

628

30

NA

NA

NA

73

113

NA

88

214

NA

104

346

219

131

507

321

149

702

444

171

929

594

50

0

0

101

67

0

216

134

0

397

232

0

633

363

0

932

518

0

1,297

708

0

1,730

952

2

8

86

61

11

183

122

14

320

206

15

497

314

22

715

445

26

975

615

33

1,276

813

5

20

82

NA

27

177

119

35

312

200

43

487

308

55

702

438

65

960

605

77

1,259

798

10

26

76

NA

35

168

114

45

299

190

56

471

298

73

681

426

86

935

589

101

1,230

773

15

59

70

NA

42

158

NA

54

287

180

66

455

288

85

662

413

100

911

572

117

1,203

747

20

NA

NA

NA

50

149

NA

63

275

169

76

440

278

97

642

401

113

888

556

131

1,176

722

30

NA

NA

NA

69

131

NA

84

250

NA

99

410

259

123

605

376

141

844

522

161

1,125

670

100

0

NA

NA

NA

0

218

NA

0

407

NA

0

665

400

0

997

560

0

1,411

770

0

1,908

1,040

2

NA

NA

NA

10

194

NA

12

354

NA

13

566

375

18

831

510

21

1,155

700

25

1,536

935

5

NA

NA

NA

26

189

NA

33

347

NA

40

557

369

52

820

504

60

1,141

692

71

1,519

926

10

NA

NA

NA

33

182

NA

43

335

NA

53

542

361

68

801

493

80

1,118

679

94

1,492

910

15

NA

NA

NA

40

174

NA

50

321

NA

62

528

353

80

782

482

93

1,095

666

109

1,465

895

20

NA

NA

NA

47

166

NA

59

311

NA

71

513

344

90

763

471

105

1,073

653

122

1,438

880

30

NA

NA

NA

NA

NA

NA

78

290

NA

92

483

NA

115

726

449

131

1,029

627

149

1,387

849

50

NA

NA

NA

NA

NA

NA

NA

NA

NA

147

428

NA

180

651

405

197

944

575

217

1,288

787

(continued)

TABLE 504.2(1)—continued
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Connected directly to vent

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

10

12

14

16

18

20

22

24

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

0

0

1,121

570

0

1,645

850

0

2,267

1,170

0

2,983

1,530

0

3,802

1,960

0

4,721

2,430

0

5,737

2,950

0

6,853

3,520

2

75

675

455

103

982

650

138

1,346

890

178

1,769

1,170

225

2,250

1,480

296

2,782

1,850

360

3,377

2,220

426

4,030

2,670

4

110

668

445

147

975

640

191

1,338

880

242

1,761

1,160

300

2,242

1,475

390

2,774

1,835

469

3,370

2,215

555

4,023

2,660

6

128

661

435

171

967

630

219

1,330

870

276

1,753

1,150

341

2,235

1,470

437

2,767

1,820

523

3,363

2,210

618

4,017

2,650

8

0

0

1,261

660

0

1,858

970

0

2,571

1,320

0

3,399

1,740

0

4,333

2,220

0

5,387

2,750

0

6,555

3,360

0

7,838

4,010

2

71

770

515

98

1,124

745

130

1,543

1,020

168

2,030

1,340

212

2,584

1,700

278

3,196

2,110

336

3,882

2,560

401

4,634

3,050

5

115

758

503

154

1,110

733

199

1,528

1,010

251

2,013

1,330

311

2,563

1,685

398

3,180

2,090

476

3,863

2,545

562

4,612

3,040

8

137

746

490

180

1,097

720

231

1,514

1,000

289

2,000

1,320

354

2,552

1,670

450

3,163

2,070

537

3,850

2,530

630

4,602

3,030

10

0

0

1,377

720

0

2,036

1,060

0

2,825

1,450

0

3,742

1,925

0

4,782

2,450

0

5,955

3,050

0

7,254

3,710

0

8,682

4,450

2

68

852

560

93

1,244

850

124

1,713

1,130

161

2,256

1,480

202

2,868

1,890

264

3,556

2,340

319

4,322

2,840

378

5,153

3,390

5

112

839

547

149

1,229

829

192

1,696

1,105

243

2,238

1,461

300

2,849

1,871

382

3,536

2,318

458

4,301

2,818

540

5,132

3,371

10

142

817

525

187

1,204

795

238

1,669

1,080

298

2,209

1,430

364

2,818

1,840

459

3,504

2,280

546

4,268

2,780

641

5,099

3,340

15

0

0

1,596

840

0

2,380

1,240

0

3,323

1,720

0

4,423

2,270

0

5,678

2,900

0

7,099

3,620

0

8,665

4,410

0

10,393

5,300

2

63

1,019

675

86

1,495

985

114

2,062

1,350

147

2,719

1,770

186

3,467

2,260

239

4,304

2,800

290

5,232

3,410

346

6,251

4,080

5

105

1,003

660

140

1,476

967

182

2,041

1,327

229

2,696

1,748

283

3,442

2,235

355

4,278

2,777

426

5,204

3,385

501

6,222

4,057

10

135

977

635

177

1,446

936

227

2,009

1,289

283

2,659

1,712

346

3,402

2,193

432

4,234

2,739

510

5,159

3,343

599

6,175

4,019

15

155

953

610

202

1,418

905

257

1,976

1,250

318

2,623

1,675

385

3,363

2,150

479

4,192

2,700

564

5,115

3,300

665

6,129

3,980

20

0

0

1,756

930

0

2,637

1,350

0

3,701

1,900

0

4,948

2,520

0

6,376

3,250

0

7,988

4,060

0

9,785

4,980

0

11,753

6,000

2

59

1,150

755

81

1,694

1,100

107

2,343

1,520

139

3,097

2,000

175

3,955

2,570

220

4,916

3,200

269

5,983

3,910

321

7,154

4,700

5

101

1,133

738

135

1,674

1,079

174

2,320

1,498

219

3,071

1,978

270

3,926

2,544

337

4,885

3,174

403

5,950

3,880

475

7,119

4,662

10

130

1,105

710

172

1,641

1,045

220

2,282

1,460

273

3,029

1,940

334

3,880

2,500

413

4,835

3,130

489

5,896

3,830

573

7,063

4,600

15

150

1,078

688

195

1,609

1,018

248

2,245

1,425

306

2,988

1,910

372

3,835

2,465

459

4,786

3,090

541

5,844

3,795

631

7,007

4,575

20

167

1,052

665

217

1,578

990

273

2,210

1,390

335

2,948

1,880

404

3,791

2,430

495

4,737

3,050

585

5,792

3,760

689

6,953

4,550

(continued)

TABLE 504.2(1)—continued
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Connected directly to vent

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

10

12

14

16

18

20

22

24

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

30

0

0

1,977

1,060

0

3,004

1,550

0

4,252

2,170

0

5,725

2,920

0

7,420

3,770

0

9,341

4,750

0

11,483

5,850

0

13,848

7,060

2

54

1,351

865

74

2,004

1,310

98

2,786

1,800

127

3,696

2,380

159

4,734

3,050

199

5,900

3,810

241

7,194

4,650

285

8,617

5,600

5

96

1,332

851

127

1,981

1,289

164

2,759

1,775

206

3,666

2,350

252

4,701

3,020

312

5,863

3,783

373

7,155

4,622

439

8,574

5,552

10

125

1,301

829

164

1,944

1,254

209

2,716

1,733

259

3,617

2,300

316

4,647

2,970

386

5,803

3,739

456

7,090

4,574

535

8,505

5,471

15

143

1,272

807

187

1,908

1,220

237

2,674

1,692

292

3,570

2,250

354

4,594

2,920

431

5,744

3,695

507

7,026

4,527

590

8,437

5,391

20

160

1,243

784

207

1,873

1,185

260

2,633

1,650

319

3,523

2,200

384

4,542

2,870

467

5,686

3,650

548

6,964

4,480

639

8,370

5,310

30

195

1,189

745

246

1,807

1,130

305

2,555

1,585

369

3,433

2,130

440

4,442

2,785

540

5,574

3,565

635

6,842

4,375

739

8,239

5,225

50

0

0

2,231

1,195

0

3,441

1,825

0

4,934

2,550

0

6,711

3,440

0

8,774

4,460

0

11,129

5,635

0

13,767

6,940

0

16,694

8,430

2

41

1,620

1,010

66

2,431

1,513

86

3,409

2,125

113

4,554

2,840

141

5,864

3,670

171

7,339

4,630

209

8,980

5,695

251

10,788

6,860

5

90

1,600

996

118

2,406

1,495

151

3,380

2,102

191

4,520

2,813

234

5,826

3,639

283

7,295

4,597

336

8,933

5,654

394

10,737

6,818

10

118

1,567

972

154

2,366

1,466

196

3,332

2,064

243

4,464

2,767

295

5,763

3,585

355

7,224

4,542

419

8,855

5,585

491

10,652

6,749

15

136

1,536

948

177

2,327

1,437

222

3,285

2,026

274

4,409

2,721

330

5,701

3,534

396

7,155

4,511

465

8,779

5,546

542

10,570

6,710

20

151

1,505

924

195

2,288

1,408

244

3,239

1,987

300

4,356

2,675

361

5,641

3,481

433

7,086

4,479

506

8,704

5,506

586

10,488

6,670

30

183

1,446

876

232

2,214

1,349

287

3,150

1,910

347

4,253

2,631

412

5,523

3,431

494

6,953

4,421

577

8,557

5,444

672

10,328

6,603

100

0

0

2,491

1,310

0

3,925

2,050

0

5,729

2,950

0

7,914

4,050

0

10,485

5,300

0

13,454

6,700

0

16,817

8,600

0

20,578

10,300

2

30

1,975

1,170

44

3,027

1,820

72

4,313

2,550

95

5,834

3,500

120

7,591

4,600

138

9,577

5,800

169

11,803

7,200

204

14,264

8,800

5

82

1,955

1,159

107

3,002

1,803

136

4,282

2,531

172

5,797

3,475

208

7,548

4,566

245

9,528

5,769

293

11,748

7,162

341

14,204

8,756

10

108

1,923

1,142

142

2,961

1,775

180

4,231

2,500

223

5,737

3,434

268

7,478

4,509

318

9,447

5,717

374

11,658

7,100

436

14,105

8,683

15

126

1,892

1,124

163

2,920

1,747

206

4,182

2,469

252

5,678

3,392

304

7,409

4,451

358

9,367

5,665

418

11,569

7,037

487

14,007

8,610

20

141

1,861

1,107

181

2,880

1,719

226

4,133

2,438

277

5,619

3,351

330

7,341

4,394

387

9,289

5,613

452

11,482

6,975

523

13,910

8,537

30

170

1,802

1,071

215

2,803

1,663

265

4,037

2,375

319

5,505

3,267

378

7,209

4,279

446

9,136

5,509

514

11,310

6,850

592

13,720

8,391

50

241

1,688

1,000

292

2,657

1,550

350

3,856

2,250

415

5,289

3,100

486

6,956

4,050

572

8,841

5,300

659

10,979

6,600

752

13,354

8,100

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.2(2)
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

0

38

77

45

59

151

85

85

249

140

126

373

204

165

522

284

211

695

369

267

894

469

371

1,118

569

537

1,639

849

2

39

51

36

60

96

66

85

156

104

123

231

156

159

320

213

201

423

284

251

541

368

347

673

453

498

979

648

4

NA

NA

33

74

92

63

102

152

102

146

225

152

187

313

208

237

416

277

295

533

360

409

664

443

584

971

638

6

NA

NA

31

83

89

60

114

147

99

163

220

148

207

307

203

263

409

271

327

526

352

449

656

433

638

962

627

8

0

37

83

50

58

164

93

83

273

154

123

412

234

161

580

319

206

777

414

258

1,002

536

360

1,257

658

521

1,852

967

2

39

56

39

59

108

75

83

176

119

121

261

179

155

363

246

197

482

321

246

617

417

339

768

513

486

1,120

743

5

NA

NA

37

77

102

69

107

168

114

151

252

171

193

352

235

245

470

311

305

604

404

418

754

500

598

1,104

730

8

NA

NA

33

90

95

64

122

161

107

175

243

163

223

342

225

280

458

300

344

591

392

470

740

486

665

1,089

715

10

0

37

87

53

57

174

99

82

293

165

120

444

254

158

628

344

202

844

449

253

1,093

584

351

1,373

718

507

2,031

1,057

2

39

61

41

59

117

80

82

193

128

119

287

194

153

400

272

193

531

354

242

681

456

332

849

559

475

1,242

848

5

52

56

39

76

111

76

105

185

122

148

277

186

190

388

261

241

518

344

299

667

443

409

834

544

584

1,224

825

10

NA

NA

34

97

100

68

132

171

112

188

261

171

237

369

241

296

497

325

363

643

423

492

808

520

688

1,194

788

15

0

36

93

57

56

190

111

80

325

186

116

499

283

153

713

388

195

966

523

244

1,259

681

336

1,591

838

488

2,374

1,237

2

38

69

47

57

136

93

80

225

149

115

337

224

148

473

314

187

631

413

232

812

543

319

1,015

673

457

1,491

983

5

51

63

44

75

128

86

102

216

140

144

326

217

182

459

298

231

616

400

287

795

526

392

997

657

562

1,469

963

10

NA

NA

39

95

116

79

128

201

131

182

308

203

228

438

284

284

592

381

349

768

501

470

966

628

664

1,433

928

15

NA

NA

NA

NA

NA

72

158

186

124

220

290

192

272

418

269

334

568

367

404

742

484

540

937

601

750

1,399

894

20

0

35

96

60

54

200

118

78

346

201

114

537

306

149

772

428

190

1,053

573

238

1,379

750

326

1,751

927

473

2,631

1,346

2

37

74

50

56

148

99

78

248

165

113

375

248

144

528

344

182

708

468

227

914

611

309

1,146

754

443

1,689

1,098

5

50

68

47

73

140

94

100

239

158

141

363

239

178

514

334

224

692

457

279

896

596

381

1,126

734

547

1,665

1,074

10

NA

NA

41

93

129

86

125

223

146

177

344

224

222

491

316

277

666

437

339

866

570

457

1,092

702

646

1,626

1,037

15

NA

NA

NA

NA

NA

80

155

208

136

216

325

210

264

469

301

325

640

419

393

838

549

526

1,060

677

730

1,587

1,005

20

NA

NA

NA

NA

NA

NA

186

192

126

254

306

196

309

448

285

374

616

400

448

810

526

592

1,028

651

808

1,550

973

(continued)

TABLE 504.2(2)
TYPE B DOUBLE-WALL GAS VENT

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

30

0

34

99

63

53

211

127

76

372

219

110

584

334

144

849

472

184

1,168

647

229

1,542

852

312

1,971

1,056

454

2,996

1,545

2

37

80

56

55

164

111

76

281

183

109

429

279

139

610

392

175

823

533

219

1,069

698

296

1,346

863

424

1,999

1,308

5

49

74

52

72

157

106

98

271

173

136

417

271

171

595

382

215

806

521

269

1,049

684

366

1,324

846

524

1,971

1,283

10

NA

NA

NA

91

144

98

122

255

168

171

397

257

213

570

367

265

777

501

327

1,017

662

440

1,287

821

620

1,927

1,234

15

NA

NA

NA

115

131

NA

151

239

157

208

377

242

255

547

349

312

750

481

379

985

638

507

1,251

794

702

1,884

1,205

20

NA

NA

NA

NA

NA

NA

181

223

NA

246

357

228

298

524

333

360

723

461

433

955

615

570

1,216

768

780

1,841

1,166

30

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

389

477

305

461

670

426

541

895

574

704

1,147

720

937

1,759

1,101

50

0

33

99

66

51

213

133

73

394

230

105

629

361

138

928

515

176

1,292

704

220

1,724

948

295

2,223

1,189

428

3,432

1,818

2

36

84

61

53

181

121

73

318

205

104

495

312

133

712

443

168

971

613

209

1,273

811

280

1,615

1,007

401

2,426

1,509

5

48

80

NA

70

174

117

94

308

198

131

482

305

164

696

435

204

953

602

257

1,252

795

347

1,591

991

496

2,396

1,490

10

NA

NA

NA

89

160

NA

118

292

186

162

461

292

203

671

420

253

923

583

313

1,217

765

418

1,551

963

589

2,347

1,455

15

NA

NA

NA

112

148

NA

145

275

174

199

441

280

244

646

405

299

894

562

363

1,183

736

481

1,512

934

668

2,299

1,421

20

NA

NA

NA

NA

NA

NA

176

257

NA

236

420

267

285

622

389

345

866

543

415

1,150

708

544

1,473

906

741

2,251

1,387

30

NA

NA

NA

NA

NA

NA

NA

NA

NA

315

376

NA

373

573

NA

442

809

502

521

1,086

649

674

1,399

848

892

2,159

1,318

100

0

NA

NA

NA

49

214

NA

69

403

NA

100

659

395

131

991

555

166

1,404

765

207

1,900

1,033

273

2,479

1,300

395

3,912

2,042

2

NA

NA

NA

51

192

NA

70

351

NA

98

563

373

125

828

508

158

1,152

698

196

1,532

933

259

1,970

1,168

371

3,021

1,817

5

NA

NA

NA

67

186

NA

90

342

NA

125

551

366

156

813

501

194

1,134

688

240

1,511

921

322

1,945

1,153

460

2,990

1,796

10

NA

NA

NA

85

175

NA

113

324

NA

153

532

354

191

789

486

238

1,104

672

293

1,477

902

389

1,905

1,133

547

2,938

1,763

15

NA

NA

NA

132

162

NA

138

310

NA

188

511

343

230

764

473

281

1,075

656

342

1,443

884

447

1,865

1,110

618

2,888

1,730

20

NA

NA

NA

NA

NA

NA

168

295

NA

224

487

NA

270

739

458

325

1,046

639

391

1,410

864

507

1,825

1,087

690

2,838

1,696

30

NA

NA

NA

NA

NA

NA

231

264

NA

301

448

NA

355

685

NA

418

988

NA

491

1,343

824

631

1,747

1,041

834

2,739

1,627

50

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

540

584

NA

617

866

NA

711

1,205

NA

895

1,591

NA

1,138

2,547

1,489

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE TABLE 504.2(3)
MASONRY CHIMNEY

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Type B double-wall connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

TYPE B DOUBLE-WALL CONNECTOR DIAMETER—(D) inches

to be used with chimney areas within the size limits at bottom

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

2

NA

NA

28

NA

NA

52

NA

NA

86

NA

NA

130

NA

NA

180

NA

NA

247

NA

NA

320

NA

NA

401

NA

NA

581

5

NA

NA

25

NA

NA

49

NA

NA

82

NA

NA

117

NA

NA

165

NA

NA

231

NA

NA

298

NA

NA

376

NA

NA

561

8

2

NA

NA

29

NA

NA

55

NA

NA

93

NA

NA

145

NA

NA

198

NA

NA

266

84

590

350

100

728

446

139

1,024

651

5

NA

NA

26

NA

NA

52

NA

NA

88

NA

NA

134

NA

NA

183

NA

NA

247

NA

NA

328

149

711

423

201

1,007

640

8

NA

NA

24

NA

NA

48

NA

NA

83

NA

NA

127

NA

NA

175

NA

NA

239

NA

NA

318

173

695

410

231

990

623

10

2

NA

NA

31

NA

NA

61

NA

NA

103

NA

NA

162

NA

NA

221

68

519

298

82

655

388

98

810

491

136

1,144

724

5

NA

NA

28

NA

NA

57

NA

NA

96

NA

NA

148

NA

NA

204

NA

NA

277

124

638

365

146

791

466

196

1,124

712

10

NA

NA

25

NA

NA

50

NA

NA

87

NA

NA

139

NA

NA

191

NA

NA

263

155

610

347

182

762

444

240

1,093

668

15

2

NA

NA

35

NA

NA

67

NA

NA

114

NA

NA

179

53

475

250

64

613

336

77

779

441

92

968

562

127

1,376

841

5

NA

NA

35

NA

NA

62

NA

NA

107

NA

NA

164

NA

NA

231

99

594

313

118

759

416

139

946

533

186

1,352

828

10

NA

NA

28

NA

NA

55

NA

NA

97

NA

NA

153

NA

NA

216

126

565

296

148

727

394

173

912

567

229

1,315

777

15

NA

NA

NA

NA

NA

48

NA

NA

89

NA

NA

141

NA

NA

201

NA

NA

281

171

698

375

198

880

485

259

1,280

742

20

2

NA

NA

38

NA

NA

74

NA

NA

124

NA

NA

201

51

522

274

61

678

375

73

867

491

87

1,083

627

121

1,548

953

5

NA

NA

36

NA

NA

68

NA

NA

116

NA

NA

184

80

503

254

95

658

350

113

845

463

133

1,059

597

179

1,523

933

10

NA

NA

NA

NA

NA

60

NA

NA

107

NA

NA

172

NA

NA

237

122

627

332

143

811

440

167

1,022

566

221

1,482

879

15

NA

NA

NA

NA

NA

NA

NA

NA

97

NA

NA

159

NA

NA

220

NA

NA

314

165

780

418

191

987

541

251

1,443

840

20

NA

NA

NA

NA

NA

NA

NA

NA

83

NA

NA

148

NA

NA

206

NA

NA

296

186

750

397

214

955

513

277

1,406

807

(continued)

TABLE 504.2(3)—continued
MASONRY CHIMNEY

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Type B double-wall connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

TYPE B DOUBLE-WALL CONNECTOR DIAMETER—(D) inches

to be used with chimney areas within the size limits at bottom

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

30

2

NA

NA

41

NA

NA

82

NA

NA

137

NA

NA

216

47

581

303

57

762

421

68

985

558

81

1,240

717

111

1,793

1,112

5

NA

NA

NA

NA

NA

76

NA

NA

128

NA

NA

198

75

561

281

90

741

393

106

962

526

125

1,216

683

169

1,766

1,094

10

NA

NA

NA

NA

NA

67

NA

NA

115

NA

NA

184

NA

NA

263

115

709

373

135

927

500

158

1,176

648

210

1,721

1,025

15

NA

NA

NA

NA

NA

NA

NA

NA

107

NA

NA

171

NA

NA

243

NA

NA

353

156

893

476

181

1,139

621

239

1,679

981

20

NA

NA

NA

NA

NA

NA

NA

NA

91

NA

NA

159

NA

NA

227

NA

NA

332

176

860

450

203

1,103

592

264

1,638

940

30

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

188

NA

NA

288

NA

NA

416

249

1,035

555

318

1,560

877

50

2

NA

NA

NA

NA

NA

92

NA

NA

161

NA

NA

251

NA

NA

351

51

840

477

61

1,106

633

72

1,413

812

99

2,080

1,243

5

NA

NA

NA

NA

NA

NA

NA

NA

151

NA

NA

230

NA

NA

323

83

819

445

98

1,083

596

116

1,387

774

155

2,052

1,225

10

NA

NA

NA

NA

NA

NA

NA

NA

138

NA

NA

215

NA

NA

304

NA

NA

424

126

1,047

567

147

1,347

733

195

2,006

1,147

15

NA

NA

NA

NA

NA

NA

NA

NA

127

NA

NA

199

NA

NA

282

NA

NA

400

146

1,010

539

170

1,307

702

222

1,961

1,099

20

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

185

NA

NA

264

NA

NA

376

165

977

511

190

1,269

669

246

1,916

1,050

30

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

327

NA

NA

468

233

1,196

623

295

1,832

984

Minimum Internal Area of Chimney (square inches)

12

19

28

38

50

63

78

95

132

Maximum Internal Area of Chimney (square inches)

Seven times the listed appliance categorized vent area, flue collar area or draft hood outlet area.

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.2(4)
MASONRY CHIMNEY

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

SINGLE-WALL METAL CONNECTOR DIAMETER—(D) inches

to be used with chimney areas within the size limits at bottom

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

2

NA

NA

28

NA

NA

52

NA

NA

86

NA

NA

130

NA

NA

180

NA

NA

247

NA

NA

319

NA

NA

400

NA

NA

580

5

NA

NA

25

NA

NA

48

NA

NA

81

NA

NA

116

NA

NA

164

NA

NA

230

NA

NA

297

NA

NA

375

NA

NA

560

8

2

NA

NA

29

NA

NA

55

NA

NA

93

NA

NA

145

NA

NA

197

NA

NA

265

NA

NA

349

382

725

445

549

1,021

650

5

NA

NA

26

NA

NA

51

NA

NA

87

NA

NA

133

NA

NA

182

NA

NA

246

NA

NA

327

NA

NA

422

673

1,003

638

8

NA

NA

23

NA

NA

47

NA

NA

82

NA

NA

126

NA

NA

174

NA

NA

237

NA

NA

317

NA

NA

408

747

985

621

10

2

NA

NA

31

NA

NA

61

NA

NA

102

NA

NA

161

NA

NA

220

216

518

297

271

654

387

373

808

490

536

1,142

722

5

NA

NA

28

NA

NA

56

NA

NA

95

NA

NA

147

NA

NA

203

NA

NA

276

334

635

364

459

789

465

657

1,121

710

10

NA

NA

24

NA

NA

49

NA

NA

86

NA

NA

137

NA

NA

189

NA

NA

261

NA

NA

345

547

758

441

771

1,088

665

15

2

NA

NA

35

NA

NA

67

NA

NA

113

NA

NA

178

166

473

249

211

611

335

264

776

440

362

965

560

520

1,373

840

5

NA

NA

32

NA

NA

61

NA

NA

106

NA

NA

163

NA

NA

230

261

591

312

325

775

414

444

942

531

637

1,348

825

10

NA

NA

27

NA

NA

54

NA

NA

96

NA

NA

151

NA

NA

214

NA

NA

294

392

722

392

531

907

504

749

1,309

774

15

NA

NA

NA

NA

NA

46

NA

NA

87

NA

NA

138

NA

NA

198

NA

NA

278

452

692

372

606

873

481

841

1,272

738

20

2

NA

NA

38

NA

NA

73

NA

NA

123

NA

NA

200

163

520

273

206

675

374

258

864

490

252

1,079

625

508

1,544

950

5

NA

NA

35

NA

NA

67

NA

NA

115

NA

NA

183

80

NA

252

255

655

348

317

842

461

433

1,055

594

623

1,518

930

10

NA

NA

NA

NA

NA

59

NA

NA

105

NA

NA

170

NA

NA

235

312

622

330

382

806

437

517

1,016

562

733

1,475

875

15

NA

NA

NA

NA

NA

NA

NA

NA

95

NA

NA

156

NA

NA

217

NA

NA

311

442

773

414

591

979

539

823

1,434

835

20

NA

NA

NA

NA

NA

NA

NA

NA

80

NA

NA

144

NA

NA

202

NA

NA

292

NA

NA

392

663

944

510

911

1,394

800

TABLE 504.2(4)—continued
MASONRY CHIMNEY

Number of Appliances

Single

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

SINGLE-WALL METAL CONNECTOR DIAMETER—(D) inches

to be used with chimney areas within the size limits at bottom

3

4

5

6

7

8

9

10

12

APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

30

2

NA

NA

41

NA

NA

81

NA

NA

136

NA

NA

215

158

578

302

200

759

420

249

982

556

340

1,237

715

489

1,789

1,110

5

NA

NA

NA

NA

NA

75

NA

NA

127

NA

NA

196

NA

NA

279

245

737

391

306

958

524

417

1,210

680

600

1,760

1,090

10

NA

NA

NA

NA

NA

66

NA

NA

113

NA

NA

182

NA

NA

260

300

703

370

370

920

496

500

1,168

644

708

1,713

1,020

15

NA

NA

NA

NA

NA

NA

NA

NA

105

NA

NA

168

NA

NA

240

NA

NA

349

428

884

471

572

1,128

615

798

1,668

975

20

NA

NA

NA

NA

NA

NA

NA

NA

88

NA

NA

155

NA

NA

223

NA

NA

327

NA

NA

445

643

1,089

585

883

1,624

932

30

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

182

NA

NA

281

NA

NA

408

NA

NA

544

1,055

1,539

865

50

2

NA

NA

NA

NA

NA

91

NA

NA

160

NA

NA

250

NA

NA

350

191

837

475

238

1,103

631

323

1,408

810

463

2,076

1,240

5

NA

NA

NA

NA

NA

NA

NA

NA

149

NA

NA

228

NA

NA

321

NA

NA

442

293

1,078

593

398

1,381

770

571

2,044

1,220

10

NA

NA

NA

NA

NA

NA

NA

NA

136

NA

NA

212

NA

NA

301

NA

NA

420

355

1,038

562

447

1,337

728

674

1,994

1,140

15

NA

NA

NA

NA

NA

NA

NA

NA

124

NA

NA

195

NA

NA

278

NA

NA

395

NA

NA

533

546

1,294

695

761

1,945

1,090

20

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

180

NA

NA

258

NA

NA

370

NA

NA

504

616

1,251

660

844

1,898

1,040

30

NA

NA

NA

NA

NA

48

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

318

NA

NA

458

NA

NA

610

1,009

1,805

970

Minimum Internal Area of Chimney (square inches)

12

19

28

38

50

63

78

95

132

Maximum Internal Area of Chimney (square inches)

Seven times the listed appliance categorized vent area, flue collar area or draft hood outlet area.

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.2(5)
SINGLE-WALL METAL PIPE OR TYPE B
ASBESTOS CEMENT VENT

Number of Appliances

Single

Appliance Type

Draft hood equipped

Appliance Vent Connection

Connected directly to pipe or vent

HEIGHT
(H)
(feet)

LATERAL
(L)
(feet)

VENT DIAMETER—(D) inches

3

4

5

6

7

8

10

12

MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

6

0

39

70

116

170

232

312

500

750

2

31

55

94

141

194

260

415

620

5

28

51

88

128

177

242

390

600

8

0

42

76

126

185

252

340

542

815

2

32

61

102

154

210

284

451

680

5

29

56

95

141

194

264

430

648

10

24

49

86

131

180

250

406

625

10

0

45

84

138

202

279

372

606

912

2

35

67

111

168

233

311

505

760

5

32

61

104

153

215

289

480

724

10

27

54

94

143

200

274

455

700

15

NA

46

84

130

186

258

432

666

15

0

49

91

151

223

312

420

684

1,040

2

39

72

122

186

260

350

570

865

5

35

67

110

170

240

325

540

825

10

30

58

103

158

223

308

514

795

15

NA

50

93

144

207

291

488

760

20

NA

NA

82

132

195

273

466

726

20

0

53

101

163

252

342

470

770

1,190

2

42

80

136

210

286

392

641

990

5

38

74

123

192

264

364

610

945

10

32

65

115

178

246

345

571

910

15

NA

55

104

163

228

326

550

870

20

NA

NA

91

149

214

306

525

832

30

0

56

108

183

276

384

529

878

1,370

2

44

84

148

230

320

441

730

1,140

5

NA

78

137

210

296

410

694

1,080

10

NA

68

125

196

274

388

656

1,050

15

NA

NA

113

177

258

366

625

1,000

20

NA

NA

99

163

240

344

596

960

30

NA

NA

NA

NA

192

295

540

890

50

0

NA

120

210

310

443

590

980

1,550

2

NA

95

171

260

370

492

820

1,290

5

NA

NA

159

234

342

474

780

1,230

10

NA

NA

146

221

318

456

730

1,190

15

NA

NA

NA

200

292

407

705

1,130

20

NA

NA

NA

185

276

384

670

1,080

30

NA

NA

NA

NA

222

330

605

1,010

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.2(6)
EXTERIOR MASONRY CHIMNEY

Number of Appliances

Single

Appliance Type

NAT

Appliance Vent Connection

Type B double-wall connector

MINIMUM ALLOWABLE INPUT RATING OF SPACE-HEATING APPLIANCE
IN THOUSANDS OF BTU PER HOUR

VENT HEIGHT
(feet)

Internal area of chimney (square inches)

12

19

28

38

50

63

78

113

37°F or Greater

Local 99% Winter Design Temperature: 37°F or Greater

6

0

0

0

0

0

0

0

0

8

0

0

0

0

0

0

0

0

10

0

0

0

0

0

0

0

0

15

NA

0

0

0

0

0

0

0

20

NA

NA

123

190

249

184

0

0

30

NA

NA

NA

NA

NA

393

334

0

50

NA

NA

NA

NA

NA

NA

NA

579

27 to 36°F

Local 99% Winter Design Temperature: 27 to 36°F

6

0

0

68

116

156

180

212

266

8

0

0

82

127

167

187

214

263

10

0

51

97

141

183

201

225

265

15

NA

NA

NA

NA

233

253

274

305

20

NA

NA

NA

NA

NA

307

330

362

30

NA

NA

NA

NA

NA

419

445

485

50

NA

NA

NA

NA

NA

NA

NA

763

17 to 26°F

Local 99% Winter Design Temperature: 17 to 26°F

6

NA

NA

NA

NA

NA

215

259

349

8

NA

NA

NA

NA

197

226

264

352

10

NA

NA

NA

NA

214

245

278

358

15

NA

NA

NA

NA

NA

296

331

398

20

NA

NA

NA

NA

NA

352

387

457

30

NA

NA

NA

NA

NA

NA

507

581

50

NA

NA

NA

NA

NA

NA

NA

NA

5 to 16°F

Local 99% Winter Design Temperature: 5 to 16°F

6

NA

NA

NA

NA

NA

NA

NA

416

8

NA

NA

NA

NA

NA

NA

312

423

10

NA

NA

NA

NA

NA

289

331

430

15

NA

NA

NA

NA

NA

NA

393

485

20

NA

NA

NA

NA

NA

NA

450

547

30

NA

NA

NA

NA

NA

NA

NA

682

50

NA

NA

NA

NA

NA

NA

NA

972

-10 to 4°F

Local 99% Winter Design Temperature: -10 to 4°F

6

NA

NA

NA

NA

NA

NA

NA

484

8

NA

NA

NA

NA

NA

NA

NA

494

10

NA

NA

NA

NA

NA

NA

NA

513

15

NA

NA

NA

NA

NA

NA

NA

586

20

NA

NA

NA

NA

NA

NA

NA

650

30

NA

NA

NA

NA

NA

NA

NA

805

50

NA

NA

NA

NA

NA

NA

NA

1,003

-11°F or Lower

Local 99% Winter Design Temperature: -11°F or Lower

Not recommended for any vent configurations

Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.

For SI: °C = [(°F - 32]/1.8, 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

These venting tables shall not be used where obstructions, as described in Section 503.15, are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions or in accordance with the following:

1. The maximum capacity of the vent system shall be determined using the “NAT Max” column.

2. The minimum capacity shall be determined as if the appliance were a fan-assisted appliance, using the “FAN Min” column to determine the minimum capacity of the vent system. Where the corresponding “FAN Min” is “NA,” the vent configuration shall not be permitted and an alternative venting configuration shall be utilized.

Where the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the smaller size shall be permitted to be used provided that all of the following requirements are met:

1. The total vent height (H) is at least 10 feet (3048 mm).

2. Vents for appliance draft hood outlets or flue collars 12 inches (305 mm) in diameter or smaller are not reduced more than one table size.

3. Vents for appliance draft hood outlets or flue collars larger than 12 inches (305 mm) in diameter are not reduced more than two table sizes.

4. The maximum capacity listed in the tables for a fan-assisted appliance is reduced by 10 percent (0.90 × maximum table capacity).

5. The draft hood outlet is greater than 4 inches (102 mm) in diameter. Do not connect a 3-inch-diameter (76 mm) vent to a 4-inch-diameter (102 mm) draft hood outlet. This provision shall not apply to fan-assisted appliances.

Single-appliance venting configurations with zero (0) lateral lengths in Tables 504.2(1), 504.2(2) and 504.2(5) shall not have elbows in the venting system. Single-appliance venting configurations with lateral lengths include two 90-degree (1.57 rad) elbows. For each additional elbow up to and including 45 degrees (0.79 rad), the maximum capacity listed in the venting tables shall be reduced by 5 percent. For each additional elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum capacity listed in the venting tables shall be reduced by 10 percent. Where multiple offsets occur in a vent, the total lateral length of all offsets combined shall not exceed that specified in Tables 504.2(1) through 504.2(5).
Zero (0) lateral (L) shall apply only to a straight vertical vent attached to a top outlet draft hood or flue collar.
Sea-level input ratings shall be used when determining maximum capacity for high altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high altitude installation.
For appliances with more than one input rate, the minimum vent capacity (FAN Min) determined from the tables shall be less than the lowest appliance input rating, and the maximum vent capacity (FAN Max/NAT Max) determined from the tables shall be greater than the highest appliance rating input.

Listed corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 504.2(1) or 504.2(2) for Type B vents with the maximum capacity reduced by 20 percent (0.80 ´ maximum capacity) and the minimum capacity as shown in Table 504.2(1) or 504.2(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Section 504.2.3. The 20-percent reduction for corrugated metallic chimney liner systems includes an allowance for one long-radius 90-degree (1.57 rad) turn at the bottom of the liner.

Connections between chimney liners and listed double-wall connectors shall be made with listed adapters designed for such purpose.

Where the vertical vent has a larger diameter than the vent connector, the vertical vent diameter shall be used to determine the minimum vent capacity, and the connector diameter shall be used to determine the maximum vent capacity. The flow area of the vertical vent shall not exceed seven times the flow area of the listed appliance categorized vent area, flue collar area or draft hood outlet area unless designed in accordance with approved engineering methods.

Tables 504.2(1), 504.2(2), 504.2(3), 504.2(4) and 504.2(5) shall be used only for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. A Type B vent shall not be considered to be exposed to the outdoors where it passes through an unventilated enclosure or chase insulated to a value of not less than R8.

TABLE 504.2(3) in combination with Table 504.2(6) shall be used for clay-tile-lined exterior masonry chimneys, provided that all of the following are met:

1. Vent connector is a Type B double wall.

2. Vent connector length is limited to 11/2 feet for each inch (18 mm per mm) of vent connector diameter.

3. The appliance is draft hood equipped.

4. The input rating is less than the maximum capacity given by Table 504.2(3).

5. For a water heater, the outdoor design temperature is not less than 5°F (-15°C).

6. For a space-heating appliance, the input rating is greater than the minimum capacity given by Table 504.2(6).


Exception: The installation of vents serving listed appliances shall be permitted to be in accordance with the appliance manufacturer’s installation instructions.
Corrugated vent connectors shall be not smaller than the listed appliance categorized vent diameter, flue collar diameter or draft hood outlet diameter.
Vent connectors shall not be increased in size more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter or draft hood outlet diameter.
In a single run of vent or vent connector, different diameters and types of vent and connector components shall be permitted to be used, provided that all such sizes and types are permitted by the tables.
Draft hood conversion accessories for use with masonry chimneys venting listed Category I fan-assisted appliances shall be listed and installed in accordance with the manufacturer’s installation instructions for such listed accessories.
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between the table entries (see Example 3, Appendix B).
Extrapolation beyond the table entries shall not be permitted.
For vent heights less than 6 feet (1829 mm) and greater than shown in the tables, engineering methods shall be used to calculate vent capacities.

The application of Tables 504.3(1) through 504.3(7) shall be subject to the requirements of Sections 504.3.1 through 504.3.27.

TABLE 504.3(1)
TYPE B DOUBLE-WALL VENT

Number of Appliances

Two or more

Appliance Type

Category I

Appliance Vent Connection

Type B double-wall connector

VENT CONNECTOR CAPACITY

VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

TYPE B DOUBLE-WALL VENT AND CONNECTOR DIAMETER—(D) inches

3

4

5

6

7

8

9

10

APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

1

22

37

26

35

66

46

46

106

72

58

164

104

77

225

142

92

296

185

109

376

237

128

466

289

2

23

41

31

37

75

55

48

121

86

60

183

124

79

253

168

95

333

220

112

424

282

131

526

345

3

24

44

35

38

81

62

49

132

96

62

199

139

82

275

189

97

363

248

114

463

317

134

575

386

8

1

22

40

27

35

72

48

49

114

76

64

176

109

84

243

148

100

320

194

118

408

248

138

507

303

2

23

44

32

36

80

57

51

128

90

66

195

129

86

269

175

103

356

230

121

454

294

141

564

358

3

24

47

36

37

87

64

53

139

101

67

210

145

88

290

198

105

384

258

123

492

330

143

612

402

10

1

22

43

28

34

78

50

49

123

78

65

189

113

89

257

154

106

341

200

125

436

257

146

542

314

2

23

47

33

36

86

59

51

136

93

67

206

134

91

282

182

109

374

238

128

479

305

149

596

372

3

24

50

37

37

92

67

52

146

104

69

220

150

94

303

205

111

402

268

131

515

342

152

642

417

15

1

21

50

30

33

89

53

47

142

83

64

220

120

88

298

163

110

389

214

134

493

273

162

609

333

2

22

53

35

35

96

63

49

153

99

66

235

142

91

320

193

112

419

253

137

532

323

165

658

394

3

24

55

40

36

102

71

51

163

111

68

248

160

93

339

218

115

445

286

140

565

365

167

700

444

20

1

21

54

31

33

99

56

46

157

87

62

246

125

86

334

171

107

436

224

131

552

285

158

681

347

2

22

57

37

34

105

66

48

167

104

64

259

149

89

354

202

110

463

265

134

587

339

161

725

414

3

23

60

42

35

110

74

50

176

116

66

271

168

91

371

228

113

486

300

137

618

383

164

764

466

30

1

20

62

33

31

113

59

45

181

93

60

288

134

83

391

182

103

512

238

125

649

305

151

802

372

2

21

64

39

33

118

70

47

190

110

62

299

158

85

408

215

105

535

282

129

679

360

155

840

439

3

22

66

44

34

123

79

48

198

124

64

309

178

88

423

242

108

555

317

132

706

405

158

874

494

50

1

19

71

36

30

133

64

43

216

101

57

349

145

78

477

197

97

627

257

120

797

330

144

984

403

2

21

73

43

32

137

76

45

223

119

59

358

172

81

490

234

100

645

306

123

820

392

148

1,014

478

3

22

75

48

33

141

86

46

229

134

61

366

194

83

502

263

103

661

343

126

842

441

151

1,043

538

100

1

18

82

37

28

158

66

40

262

104

53

442

150

73

611

204

91

810

266

112

1,038

341

135

1,285

417

2

19

83

44

30

161

79

42

267

123

55

447

178

75

619

242

94

822

316

115

1,054

405

139

1,306

494

3

20

84

50

31

163

89

44

272

138

57

452

109

78

627

272

97

834

355

118

1,069

455

142

1,327

555


COMMON VENT CAPACITY

VENT HEIGHT
(H)
(feet)

TYPE B DOUBLE-WALL COMMON VENT DIAMETER (D)—inches

4

5

6

7

8

9

10

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

6

92

81

65

140

116

103

204

161

147

309

248

200

404

314

260

547

434

335

672

520

410

8

101

90

73

155

129

114

224

178

163

339

275

223

444

348

290

602

480

378

740

577

465

10

110

97

79

169

141

124

243

194

178

367

299

242

477

377

315

649

522

405

800

627

495

15

125

112

91

195

164

144

283

228

206

427

352

280

556

444

365

753

612

465

924

733

565

20

136

123

102

215

183

160

314

255

229

475

394

310

621

499

405

842

688

523

1,035

826

640

30

152

138

118

244

210

185

361

297

266

547

459

360

720

585

470

979

808

605

1,209

975

740

50

167

153

134

279

244

214

421

353

310

641

547

423

854

706

550

1,164

977

705

1,451

1,188

860

100

175

163

NA

311

277

NA

489

421

NA

751

658

479

1,025

873

625

1,408

1,215

800

1,784

1,502

975

TABLE 504.3(1)—continued
TYPE B DOUBLE-WALL VENT

Number of Appliances

Two or more

Appliance Type

Category I

Appliance Vent Connection

Type B double-wall connector

VENT CONNECTOR CAPACITY

VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

TYPE B DOUBLE-WALL VENT AND DIAMETER—(D) inches

12

14

16

18

20

22

24

APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

2

174

764

496

223

1,046

653

281

1,371

853

346

1,772

1,080

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

180

897

616

230

1,231

827

287

1,617

1,081

352

2,069

1,370

NA

NA

NA

NA

NA

NA

NA

NA

NA

6

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

8

2

186

822

516

238

1,126

696

298

1,478

910

365

1,920

1,150

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

192

952

644

244

1,307

884

305

1,719

1,150

372

2,211

1,460

471

2,737

1,800

560

3,319

2,180

662

3,957

2,590

6

198

1,050

772

252

1,445

1,072

313

1,902

1,390

380

2,434

1,770

478

3,018

2,180

568

3,665

2,640

669

4,373

3,130

10

2

196

870

536

249

1,195

730

311

1,570

955

379

2,049

1,205

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

201

997

664

256

1,371

924

318

1,804

1,205

387

2,332

1,535

486

2,887

1,890

581

3,502

2,280

686

4,175

2,710

6

207

1,095

792

263

1,509

1,118

325

1,989

1,455

395

2,556

1,865

494

3,169

2,290

589

3,849

2,760

694

4,593

3,270

15

2

214

967

568

272

1,334

790

336

1,760

1,030

408

2,317

1,305

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

221

1,085

712

279

1,499

1,006

344

1,978

1,320

416

2,579

1,665

523

3,197

2,060

624

3,881

2,490

734

4,631

2,960

6

228

1,181

856

286

1,632

1,222

351

2,157

1,610

424

2,796

2,025

533

3,470

2,510

634

4,216

3,030

743

5,035

3,600

20

2

223

1,051

596

291

1,443

840

357

1,911

1,095

430

2,533

1,385

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

230

1,162

748

298

1,597

1,064

365

2,116

1,395

438

2,778

1,765

554

3,447

2,180

661

4,190

2,630

772

5,005

3,130

6

237

1,253

900

307

1,726

1,288

373

2,287

1,695

450

2,984

2,145

567

3,708

2,650

671

4,511

3,190

785

5,392

3,790

30

2

216

1,217

632

286

1,664

910

367

2,183

1,190

461

2,891

1,540

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

223

1,316

792

294

1,802

1,160

376

2,366

1,510

474

3,110

1,920

619

3,840

2,365

728

4,861

2,860

847

5,606

3,410

6

231

1,400

952

303

1,920

1,410

384

2,524

1,830

485

3,299

2,340

632

4,080

2,875

741

4,976

3,480

860

5,961

4,150

50

2

206

1,479

689

273

2,023

1,007

350

2,659

1,315

435

3,548

1,665

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

213

1,561

860

281

2,139

1,291

359

2,814

1,685

447

3,730

2,135

580

4,601

2,633

709

5,569

3,185

851

6,633

3,790

6

221

1,631

1,031

290

2,242

1,575

369

2,951

2,055

461

3,893

2,605

594

4,808

3,208

724

5,826

3,885

867

6,943

4,620

100

2

192

1,923

712

254

2,644

1,050

326

3,490

1,370

402

4,707

1,740

NA

NA

NA

NA

NA

NA

NA

NA

NA

4

200

1,984

888

263

2,731

1,346

336

3,606

1,760

414

4,842

2,220

523

5,982

2,750

639

7,254

3,330

769

8,650

3,950

6

208

2,035

1,064

272

2,811

1,642

346

3,714

2,150

426

4,968

2,700

539

6,143

3,350

654

7,453

4,070

786

8,892

4,810

COMMON VENT CAPACITY

VENT HEIGHT
(H)
(feet)

TYPE B DOUBLE-WALL COMMON VENT DIAMETER—(D) inches

12

14

16

18

20

22

24

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

6

900

696

588

1,284

990

815

1,735

1,336

1,065

2,253

1,732

1,345

2,838

2,180

1,660

3,488

2,677

1970

4,206

3,226

2,390

8

994

773

652

1,423

1,103

912

1,927

1,491

1,190

2,507

1,936

1,510

3,162

2,439

1,860

3,890

2,998

2,200

4,695

3,616

2,680

10

1,076

841

712

1,542

1,200

995

2,093

1,625

1,300

2,727

2,113

1645

3,444

2,665

2,030

4,241

3,278

2,400

5,123

3,957

2,920

15

1,247

986

825

1,794

1,410

1,158

2,440

1,910

1,510

3,184

2,484

1,910

4,026

3,133

2,360

4,971

3,862

2,790

6,016

4,670

3,400

20

1,405

1,116

916

2,006

1,588

1,290

2,722

2,147

1,690

3,561

2,798

2,140

4,548

3,552

2,640

5,573

4,352

3,120

6,749

5,261

3,800

30

1,658

1,327

1,025

2,373

1,892

1,525

3,220

2,558

1,990

4,197

3,326

2,520

5,303

4,193

3,110

6,539

5,157

3,680

7,940

6,247

4,480

50

2,024

1,640

1,280

2,911

2,347

1,863

3,964

3,183

2,430

5,184

4,149

3,075

6,567

5,240

3,800

8,116

6,458

4,500

9,837

7,813

5,475

100

2,569

2,131

1,670

3,732

3,076

2,450

5,125

4,202

3,200

6,749

5,509

4,050

8,597

6,986

5,000

10,681

8,648

5,920

13,004

10,499

7,200

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.3(2)
TYPE B DOUBLE-WALL VENT

Number of Appliances

Two or more

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

VENT CONNECTOR CAPACITY

VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

SINGLE-WALL METAL VENT CONNECTOR DIAMETER—(D) inches

3

4

5

6

7

8

9

10

APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

1

NA

NA

26

NA

NA

46

NA

NA

71

NA

NA

102

207

223

140

262

293

183

325

373

234

447

463

286

2

NA

NA

31

NA

NA

55

NA

NA

85

168

182

123

215

251

167

271

331

219

334

422

281

458

524

344

3

NA

NA

34

NA

NA

62

121

131

95

175

198

138

222

273

188

279

361

247

344

462

316

468

574

385

8

1

NA

NA

27

NA

NA

48

NA

NA

75

NA

NA

106

226

240

145

285

316

191

352

403

244

481

502

299

2

NA

NA

32

NA

NA

57

125

126

89

184

193

127

234

266

173

293

353

228

360

450

292

492

560

355

3

NA

NA

35

NA

NA

64

130

138

100

191

208

144

241

287

197

302

381

256

370

489

328

501

609

400

10

1

NA

NA

28

NA

NA

50

119

121

77

182

186

110

240

253

150

302

335

196

372

429

252

506

534

308

2

NA

NA

33

84

85

59

124

134

91

189

203

132

248

278

183

311

369

235

381

473

302

517

589

368

3

NA

NA

36

89

91

67

129

144

102

197

217

148

257

299

203

320

398

265

391

511

339

528

637

413

15

1

NA

NA

29

79

87

52

116

138

81

177

214

116

238

291

158

312

380

208

397

482

266

556

596

324

2

NA

NA

34

83

94

62

121

150

97

185

230

138

246

314

189

321

411

248

407

522

317

568

646

387

3

NA

NA

39

87

100

70

127

160

109

193

243

157

255

333

215

331

438

281

418

557

360

579

690

437

20

1

49

56

30

78

97

54

115

152

84

175

238

120

233

325

165

306

425

217

390

538

276

546

664

336

2

52

59

36

82

103

64

120

163

101

182

252

144

243

346

197

317

453

259

400

574

331

558

709

403

3

55

62

40

87

107

72

125

172

113

190

264

164

252

363

223

326

476

294

412

607

375

570

750

457

30

1

47

60

31

77

110

57

112

175

89

169

278

129

226

380

175

296

497

230

378

630

294

528

779

358

2

51

62

37

81

115

67

117

185

106

177

290

152

236

397

208

307

521

274

389

662

349

541

819

425

3

54

64

42

85

119

76

122

193

120

185

300

172

244

412

235

316

542

309

400

690

394

555

855

482

50

1

46

69

34

75

128

60

109

207

96

162

336

137

217

460

188

284

604

245

364

768

314

507

951

384

2

49

71

40

79

132

72

114

215

113

170

345

164

226

473

223

294

623

293

376

793

375

520

983

458

3

52

72

45

83

136

82

119

221

123

178

353

186

235

486

252

304

640

331

387

816

423

535

1,013

518

100

1

45

79

34

71

150

61

104

249

98

153

424

140

205

585

192

269

774

249

345

993

321

476

1,236

393

2

48

80

41

75

153

73

110

255

115

160

428

167

212

593

228

279

788

299

358

1,011

383

490

1,259

469

3

51

81

46

79

157

85

114

260

129

168

433

190

222

603

256

289

801

339

368

1,027

431

506

1,280

527

COMMON VENT CAPACITY

VENT HEIGHT
(H)
(feet)

TYPE B DOUBLE-WALL COMMON VENT DIAMETER— (D) inches

4

5

6

7

8

9

10

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

6

NA

78

64

NA

113

99

200

158

144

304

244

196

398

310

257

541

429

332

665

515

407

8

NA

87

71

NA

126

111

218

173

159

331

269

218

436

342

285

592

473

373

730

569

460

10

NA

94

76

163

137

120

237

189

174

357

292

236

467

369

309

638

512

398

787

617

487

15

121

108

88

189

159

140

275

221

200

416

343

274

544

434

357

738

599

456

905

718

553

20

131

118

98

208

177

156

305

247

223

463

383

302

606

487

395

824

673

512

1,013

808

626

30

145

132

113

236

202

180

350

286

257

533

446

349

703

570

459

958

790

593

1,183

952

723

50

159

145

128

268

233

208

406

337

296

622

529

410

833

686

535

1,139

954

689

1,418

1,157

838

100

166

153

NA

297

263

NA

469

398

NA

726

633

464

999

846

606

1,378

1,185

780

1,741

1,459

948

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.


TABLE 504.3(3)
MASONRY CHIMNEY

Number of Appliances

Two or more

Appliance Type

Category I

Appliance Vent Connection

Type B double-wall connector

VENT CONNECTOR CAPACITY

VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

TYPE B DOUBLE-WALL VENT CONNECTOR DIAMETER—(D) inches

3

4

5

6

7

8

9

10

APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

1

24

33

21

39

62

40

52

106

67

65

194

101

87

274

141

104

370

201

124

479

253

145

599

319

2

26

43

28

41

79

52

53

133

85

67

230

124

89

324

173

107

436

232

127

562

300

148

694

378

3

27

49

34

42

92

61

55

155

97

69

262

143

91

369

203

109

491

270

129

633

349

151

795

439

8

1

24

39

22

39

72

41

55

117

69

71

213

105

94

304

148

113

414

210

134

539

267

156

682

335

2

26

47

29

40

87

53

57

140

86

73

246

127

97

350

179

116

473

240

137

615

311

160

776

394

3

27

52

34

42

97

62

59

159

98

75

269

145

99

383

206

119

517

276

139

672

358

163

848

452

10

1

24

42

22

38

80

42

55

130

71

74

232

108

101

324

153

120

444

216

142

582

277

165

739

348

2

26

50

29

40

93

54

57

153

87

76

261

129

103

366

184

123

498

247

145

652

321

168

825

407

3

27

55

35

41

105

63

58

170

100

78

284

148

106

397

209

126

540

281

147

705

366

171

893

463

15

1

24

48

23

38

93

44

54

154

74

72

277

114

100

384

164

125

511

229

153

658

297

184

824

375

2

25

55

31

39

105

55

56

174

89

74

299

134

103

419

192

128

558

260

156

718

339

187

900

432

3

26

59

35

41

115

64

57

189

102

76

319

153

105

448

215

131

597

292

159

760

382

190

960

486

20

1

24

52

24

37

102

46

53

172

77

71

313

119

98

437

173

123

584

239

150

752

312

180

943

397

2

25

58

31

39

114

56

55

190

91

73

335

138

101

467

199

126

625

270

153

805

354

184

1,011

452

3

26

63

35

40

123

65

57

204

104

75

353

157

104

493

222

129

661

301

156

851

396

187

1,067

505

30

1

24

54

25

37

111

48

52

192

82

69

357

127

96

504

187

119

680

255

145

883

337

175

1,115

432

2

25

60

32

38

122

58

54

208

95

72

376

145

99

531

209

122

715

287

149

928

378

179

1,171

484

3

26

64

36

40

131

66

56

221

107

74

392

163

101

554

233

125

746

317

152

968

418

182

1,220

535

50

1

23

51

25

36

116

51

51

209

89

67

405

143

92

582

213

115

798

294

140

1,049

392

168

1,334

506

2

24

59

32

37

127

61

53

225

102

70

421

161

95

604

235

118

827

326

143

1,085

433

172

1,379

558

3

26

64

36

39

135

69

55

237

115

72

435

80

98

624

260

121

854

357

147

1,118

474

176

1,421

611

100

1

23

46

24

35

108

50

49

208

92

65

428

155

88

640

237

109

907

334

134

1,222

454

161

1,589

596

2

24

53

31

37

120

60

51

224

105

67

444

174

92

660

260

113

933

368

138

1,253

497

165

1,626

651

3

25

59

35

38

130

68

53

237

118

69

458

193

94

679

285

116

956

399

141

1,282

540

169

1,661

705

COMMON VENT CAPACITY

VENT HEIGHT
(H)
(feet)

MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)

12

19

28

38

50

63

78

113

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

6

NA

74

25

NA

119

46

NA

178

71

NA

257

103

NA

351

143

NA

458

188

NA

582

246

1,041

853

NA

8

NA

80

28

NA

130

53

NA

193

82

NA

279

119

NA

384

163

NA

501

218

724

636

278

1,144

937

408

10

NA

84

31

NA

138

56

NA

207

90

NA

299

131

NA

409

177

606

538

236

776

686

302

1,226

1,010

454

15

NA

NA

36

NA

152

67

NA

233

106

NA

334

152

523

467

212

682

611

283

874

781

365

1,374

1,156

546

20

NA

NA

41

NA

NA

75

NA

250

122

NA

368

172

565

508

243

742

668

325

955

858

419

1,513

1,286

648

30

NA

NA

NA

NA

NA

NA

NA

270

137

NA

404

198

615

564

278

816

747

381

1,062

969

496

1,702

1,473

749

50

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

620

328

879

831

461

1,165

1,089

606

1,905

1,692

922

100

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

348

NA

NA

499

NA

NA

669

2,053

1,921

1,058

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.3(4)
MASONRY CHIMNEY

Number of Appliances

Two or more

Appliance Type

Category I

Appliance Vent Connection

Single-wall metal connector

VENT CONNECTOR CAPACITY

VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

SINGLE-WALL METAL VENT CONNECTOR DIAMETER (D)—inches

3

4

5

6

7

8

9

10

APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

FAN

NAT

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

Min

Max

Max

6

1

NA

NA

21

NA

NA

39

NA

NA

66

179

191

100

231

271

140

292

366

200

362

474

252

499

594

316

2

NA

NA

28

NA

NA

52

NA

NA

84

186

227

123

239

321

172

301

432

231

373

557

299

509

696

376

3

NA

NA

34

NA

NA

61

134

153

97

193

258

142

247

365

202

309

491

269

381

634

348

519

793

437

8

1

NA

NA

21

NA

NA

40

NA

NA

68

195

208

103

250

298

146

313

407

207

387

530

263

529

672

331

2

NA

NA

28

NA

NA

52

137

139

85

202

240

125

258

343

177

323

465

238

397

607

309

540

766

391

3

NA

NA

34

NA

NA

62

143

156

98

210

264

145

266

376

205

332

509

274

407

663

356

551

838

450

10

1

NA

NA

22

NA

NA

41

130

151

70

202

225

106

267

316

151

333

434

213

410

571

273

558

727

343

2

NA

NA

29

NA

NA

53

136

150

86

210

255

128

276

358

181

343

489

244

420

640

317

569

813

403

3

NA

NA

34

97

102

62

143

166

99

217

277

147

284

389

207

352

530

279

430

694

363

580

880

459

15

1

NA

NA

23

NA

NA

43

129

151

73

199

271

112

268

376

161

349

502

225

445

646

291

623

808

366

2

NA

NA

30

92

103

54

135

170

88

207

295

132

277

411

189

359

548

256

456

706

334

634

884

424

3

NA

NA

34

96

112

63

141

185

101

215

315

151

286

439

213

368

586

289

466

755

378

646

945

479

20

1

NA

NA

23

87

99

45

128

167

76

197

303

117

265

425

169

345

569

235

439

734

306

614

921

347

2

NA

NA

30

91

111

55

134

185

90

205

325

136

274

455

195

355

610

266

450

787

348

627

986

443

3

NA

NA

35

96

119

64

140

199

103

213

343

154

282

481

219

365

644

298

461

831

391

639

1,042

496

30

1

NA

NA

24

86

108

47

126

187

80

193

347

124

259

492

183

338

665

250

430

864

330

600

1,089

421

2

NA

NA

31

91

119

57

132

203

93

201

366

142

269

518

205

348

699

282

442

908

372

613

1,145

473

3

NA

NA

35

95

127

65

138

216

105

209

381

160

277

540

229

358

729

312

452

946

412

626

1,193

524

50

1

NA

NA

24

85

113

50

124

204

87

188

392

139

252

567

208

328

778

287

417

1,022

383

582

1,302

492

2

NA

NA

31

89

123

60

130

218

100

196

408

158

262

588

230

339

806

320

429

1,058

425

596

1,346

545

3

NA

NA

35

94

131

68

136

231

112

205

422

176

271

607

255

349

831

351

440

1,090

466

610

1,386

597

100

1

NA

NA

23

84

104

49

122

200

89

182

410

151

243

617

232

315

875

328

402

1,181

444

560

1,537

580

2

NA

NA

30

88

115

59

127

215

102

190

425

169

253

636

254

326

899

361

415

1,210

488

575

1,570

634

3

NA

NA

34

93

124

67

133

228

115

199

438

188

262

654

279

337

921

392

427

1,238

529

589

1,604

687

COMMON VENT CAPACITY

VENT HEIGHT
(H)
(feet)

MINIMUM INTERNAL AREA OF MASONRY CHIMNEY FLUE (square inches)

12

19

28

38

50

63

78

113

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

FAN
+FAN

FAN
+NAT

NAT
+NAT

6

NA

NA

25

NA

118

45

NA

176

71

NA

255

102

NA

348

142

NA

455

187

NA

579

245

NA

846

NA

8

NA

NA

28

NA

128

52

NA

190

81

NA

276

118

NA

380

162

NA

497

217

NA

633

277

1,136

928

405

10

NA

NA

31

NA

136

56

NA

205

89

NA

295

129

NA

405

175

NA

532

234

171

680

300

1,216

1,000

450

15

NA

NA

36

NA

NA

66

NA

230

105

NA

335

150

NA

400

210

677

602

280

866

772

360

1,359

1,139

540

20

NA

NA

NA

NA

NA

74

NA

247

120

NA

362

170

NA

503

240

765

661

321

947

849

415

1,495

1,264

640

30

NA

NA

NA

NA

NA

NA

NA

NA

135

NA

398

195

NA

558

275

808

739

377

1,052

957

490

1,682

1,447

740

50

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

612

325

NA

821

456

1,152

1,076

600

1,879

1,672

910

100

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

NA

494

NA

NA

663

2,006

1,885

1,046

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.


TABLE 504.3(5)
SINGLE-WALL METAL PIPE OR TYPE ASBESTOS CEMENT VENT

Number of Appliances

Two or more

Appliance Type

Draft hood-equipped

Appliance Vent Connection

Direct to pipe or vent

VENT CONNECTOR CAPACITY

TOTAL VENT HEIGHT
(H)
(feet)

CONNECTOR
RISE
(R)
(feet)

VENT CONNECTOR DIAMETER—(D) inches

3

4

5

6

7

8

MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

6-8

1

21

40

68

102

146

205

2

28

53

86

124

178

235

3

34

61

98

147

204

275

15

1

23

44

77

117

179

240

2

30

56

92

134

194

265

3

35

64

102

155

216

298

30 and up

1

25

49

84

129

190

270

2

31

58

97

145

211

295

3

36

68

107

164

232

321


COMMON VENT CAPACITY

TOTAL VENT HEIGHT
(H)
(feet)

COMMON VENT DIAMETER—(D) inches

4

5

6

7

8

10

12

COMBINED APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H

6

48

78

111

155

205

320

NA

8

55

89

128

175

234

365

505

10

59

95

136

190

250

395

560

15

71

115

168

228

305

480

690

20

80

129

186

260

340

550

790

30

NA

147

215

300

400

650

940

50

NA

NA

NA

360

490

810

1,190

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.


TABLE 504.3(6a)
EXTERIOR MASONRY CHIMNEY

Number of
Appliances

Two or more

Appliance
Type

NAT + NAT

Combined Appliance Maximum
Input Rating in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

6

25

46

71

103

143

188

246

NA

8

28

53

82

119

163

218

278

408

10

31

56

90

131

177

236

302

454

15

NA

67

106

152

212

283

365

546

20

NA

NA

NA

NA

NA

325

419

648

30

NA

NA

NA

NA

NA

NA

496

749

50

NA

NA

NA

NA

NA

NA

NA

922

100

NA

NA

NA

NA

NA

NA

NA

NA

TABLE 504.3(6b)
EXTERIOR MASONRY CHIMNEY

Number of
Appliances

Two or more

Appliance
Type

NAT + NAT

Appliance Vent Connection

Type B double-wall connector

Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

37°F or Greater

Local 99% Winter Design Temperature: 37°F or Greater

6

0

0

0

0

0

0

0

NA

8

0

0

0

0

0

0

0

0

10

0

0

0

0

0

0

0

0

15

NA

0

0

0

0

0

0

0

20

NA

NA

NA

NA

NA

184

0

0

30

NA

NA

NA

NA

NA

393

334

0

50

NA

NA

NA

NA

NA

NA

NA

579

100

NA

NA

NA

NA

NA

NA

NA

NA

27 to 36°F

Local 99% Winter Design Temperature: 27 to 36°F

6

0

0

68

NA

NA

180

212

NA

8

0

0

82

NA

NA

187

214

263

10

0

51

NA

NA

NA

201

225

265

15

NA

NA

NA

NA

NA

253

274

305

20

NA

NA

NA

NA

NA

307

330

362

30

NA

NA

NA

NA

NA

NA

445

485

50

NA

NA

NA

NA

NA

NA

NA

763

100

NA

NA

NA

NA

NA

NA

NA

NA

TABLE 504.3(6b)
EXTERIOR MASONRY CHIMNEY—continued

Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

17 to 26°F

Local 99% Winter Design Temperature: 17 to 26°F

6

NA

NA

NA

NA

NA

NA

NA

NA

8

NA

NA

NA

NA

NA

NA

264

352

10

NA

NA

NA

NA

NA

NA

278

358

15

NA

NA

NA

NA

NA

NA

331

398

20

NA

NA

NA

NA

NA

NA

387

457

30

NA

NA

NA

NA

NA

NA

NA

581

50

NA

NA

NA

NA

NA

NA

NA

862

100

NA

NA

NA

NA

NA

NA

NA

NA

5 to 16°F

Local 99% Winter Design Temperature: 5 to 16°F

6

NA

NA

NA

NA

NA

NA

NA

NA

8

NA

NA

NA

NA

NA

NA

NA

NA

10

NA

NA

NA

NA

NA

NA

NA

430

15

NA

NA

NA

NA

NA

NA

NA

485

20

NA

NA

NA

NA

NA

NA

NA

547

30

NA

NA

NA

NA

NA

NA

NA

682

50

NA

NA

NA

NA

NA

NA

NA

NA

100

NA

NA

NA

NA

NA

NA

NA

NA

4°F or Lower

Local 99% Winter Design Temperature: 4°F or Lower

Not recommended for any vent configurations

Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.

For SI: °C = [(°F - 32]/1.8, 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

TABLE 504.3(7a)
EXTERIOR MASONRY CHIMNEY

Number of
Appliances

Two or more

Appliance
Type

FAN + NAT

Appliance Vent Connection

Type B double-wall connector

Combined Appliance Maximum
Input Rating in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

6

74

119

178

257

351

458

582

853

8

80

130

193

279

384

501

636

937

10

84

138

207

299

409

538

686

1,010

15

NA

152

233

334

467

611

781

1,156

20

NA

NA

250

368

508

668

858

1,286

30

NA

NA

NA

404

564

747

969

1,473

50

NA

NA

NA

NA

NA

831

1,089

1,692

100

NA

NA

NA

NA

NA

NA

NA

1,921

TABLE 504.3(7b)
EXTERIOR MASONRY CHIMNEY

Number of
Appliances

Two or more

Appliance
Type

FAN + NAT

Appliance Vent Connection

Type B double-wall connector

Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

37°F or Greater

Local 99% Winter Design Temperature: 37°F or Greater

6

0

0

0

0

0

0

0

0

8

0

0

0

0

0

0

0

0

10

0

0

0

0

0

0

0

0

15

NA

0

0

0

0

0

0

0

20

NA

NA

123

190

249

184

0

0

30

NA

NA

NA

334

398

393

334

0

50

NA

NA

NA

NA

NA

714

707

579

100

NA

NA

NA

NA

NA

NA

NA

1,600

27 to 36°F

Local 99% Winter Design Temperature: 27 to 36°F

6

0

0

68

116

156

180

212

266

8

0

0

82

127

167

187

214

263

10

0

51

97

141

183

210

225

265

15

NA

111

142

183

233

253

274

305

20

NA

NA

187

230

284

307

330

362

30

NA

NA

NA

330

319

419

445

485

50

NA

NA

NA

NA

NA

672

705

763

100

NA

NA

NA

NA

NA

NA

NA

1,554

TABLE 504.3(7b)
EXTERIOR MASONRY CHIMNEY—continued


Minimum Allowable Input Rating of
Space-Heating Appliance in Thousands of Btu per Hour

VENT HEIGHT
(feet)

INTERNAL AREA OF CHIMNEY (square inches)

12

19

28

38

50

63

78

113

17 to 26°F

Local 99% Winter Design Temperature: 17 to 26°F

6

0

55

99

141

182

215

259

349

8

52

74

111

154

197

226

264

352

10

NA

90

125

169

214

245

278

358

15

NA

NA

167

212

263

296

331

398

20

NA

NA

212

258

316

352

387

457

30

NA

NA

NA

362

429

470

507

581

50

NA

NA

NA

NA

NA

723

766

862

100

NA

NA

NA

NA

NA

NA

NA

1,669

5 to 16°F

Local 99% Winter Design Temperature: 5 to 16°F

6

NA

78

121

166

214

252

301

416

8

NA

94

135

182

230

269

312

423

10

NA

111

149

198

250

289

331

430

15

NA

NA

193

247

305

346

393

485

20

NA

NA

NA

293

360

408

450

547

30

NA

NA

NA

377

450

531

580

682

50

NA

NA

NA

NA

NA

797

853

972

100

NA

NA

NA

NA

NA

NA

NA

1,833

-10 to 4°F

Local 99% Winter Design Temperature: -10 to 4°F

6

NA

NA

145

196

249

296

349

484

8

NA

NA

159

213

269

320

371

494

10

NA

NA

175

231

292

339

397

513

15

NA

NA

NA

283

351

404

457

586

20

NA

NA

NA

333

408

468

528

650

30

NA

NA

NA

NA

NA

603

667

805

50

NA

NA

NA

NA

NA

NA

955

1,003

100

NA

NA

NA

NA

NA

NA

NA

NA

-11°F or Lower

Local 99% Winter Design Temperature: -11°F or Lower

Not recommended for any vent configurations

Note: See Figure B-19 in Appendix B for a map showing local 99 percent winter design temperatures in the United States.

For SI: °C = [(°F - 32]/1.8, 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 foot = 304.8 mm, 1 British thermal unit per hour = 0.2931 W.

These venting tables shall not be used where obstructions, as described in Section 503.15, are installed in the venting system. The installation of vents serving listed appliances with vent dampers shall be in accordance with the appliance manufacturer’s instructions or in accordance with the following:

1. The maximum capacity of the vent connector shall be determined using the NAT Max column.

2. The maximum capacity of the vertical vent or chimney shall be determined using the FAN+NAT column when the second appliance is a fan-assisted appliance, or the NAT+NAT column when the second appliance is equipped with a draft hood.

3. The minimum capacity shall be determined as if the appliance were a fan-assisted appliance.

3.1. The minimum capacity of the vent connector shall be determined using the FAN Min column.

3.2. The FAN+FAN column shall be used where the second appliance is a fan-assisted appliance, and the FAN+NAT column shall be used where the second appliance is equipped with a draft hood, to determine whether the vertical vent or chimney configuration is not permitted (NA). Where the vent configuration is NA, the vent configuration shall not be permitted and an alternative venting configuration shall be utilized.

The vent connector shall be routed to the vent utilizing the shortest possible route. Except as provided in Section 504.3.3, the maximum vent connector horizontal length shall be 11/2 feet for each inch (18 mm per mm) of connector diameter as shown in Table 504.3.2.

2. For a connector serving a fan-assisted appliance, the minimum capacity (FAN Min) of the connector shall be determined by referring to the corresponding single appliance table. For Type B double-wall connectors, Table 504.2(1) shall be used. For single-wall connectors, Table 504.2(2) shall be used. The height (H) and lateral (L) shall be measured according to the procedures for a single-appliance vent, as if the other appliances were not present.

TABLE 504.3.2
MAXIMUM VENT CONNECTOR LENGTH

CONNECTOR DIAMETER MAXIMUM (inches)

CONNECTOR HORIZONTAL LENGTH (feet)

3

41/2

4

6

5

71/2

6

9

7

101/2

8

12

9

131/2

10

15

12

18

14

21

16

24

18

27

20

30

22

33

24

36

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

Connectors with longer horizontal lengths than those listed in Section 504.3.2 are permitted under the following conditions:

1. The maximum capacity (FAN Max or NAT Max) of the vent connector shall be reduced 10 percent for each additional multiple of the length allowed by Section 504.3.2. For example, the maximum length listed in Table 504.3.2 for a 4-inch (102 mm) connector is 6 feet (1829 mm). With a connector length greater than 6 feet (1829 mm) but not exceeding 12 feet (3658 mm), the maximum capacity must be reduced by 10 percent (0.90 ´ maximum vent connector capacity). With a connector length greater than 12 feet (3658 mm) but not exceeding 18 feet (5486 mm), the maximum capacity must be reduced by 20 percent (0.80 ´ maximum vent capacity).


2. For a connector serving a fan-assisted appliance, the minimum capacity (FAN Min) of the connector shall be determined by referring to the corresponding single appliance table. For Type B double-wall connectors, Table 504.2(1) shall be used. For single-wall connectors, Table 504.2(2) shall be used. The height (H) and lateral (L) shall be measured according to the procedures for a single-appliance vent, as if the other appliances were not present.

Where the vent connectors are combined prior to entering the vertical portion of the common vent to form a common vent manifold, the size of the common vent manifold and the common vent shall be determined by applying a 10-percent reduction (0.90 ´ maximum common vent capacity) to the common vent capacity part of the common vent tables. The length of the common vent connector manifold (Lm) shall not exceed 11/2 feet for each inch (18 mm per mm) of common vent connector manifold diameter (D) (see Figure B-11).
Where the common vertical vent is offset, the maximum capacity of the common vent shall be reduced in accordance with Section 504.3.6. The horizontal length of the common vent offset (Lo) shall not exceed 11/2 feet for each inch (18 mm per mm) of common vent diameter (D). Where multiple offsets occur in a common vent, the total horizontal length of all offsets combined shall not exceed 11/2 feet for each inch (18 mm per mm) of common vent diameter (D).
For each elbow up to and including 45 degrees (0.79 rad) in the common vent, the maximum common vent capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum common vent capacity listed in the venting tables shall be reduced by 10 percent.
The vent connector capacities listed in the common vent sizing tables include allowance for two 90-degree (1.57 rad) elbows. For each additional elbow up to and including 45 degrees (0.79 rad), the maximum vent connector capacity listed in the venting tables shall be reduced by 5 percent. For each elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum vent connector capacity listed in the venting tables shall be reduced by 10 percent.
The cross-sectional area of the common vent shall be equal to or greater than the cross-sectional area of the largest connector.
At the point where tee or wye fittings connect to a common vent, the opening size of the fitting shall be equal to the size of the common vent. Such fittings shall not be prohibited from having reduced- size openings at the point of connection of appliance vent connectors.
Tee and wye fittings connected to a common gas vent shall be considered as part of the common gas vent and shall be constructed of materials consistent with that of the common gas vent.
Sea-level input ratings shall be used when determining maximum capacity for high-altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high-altitude installation.
Connector rise (R) for each appliance connector shall be measured from the draft hood outlet or flue collar to the centerline where the vent gas streams come together.
For multiple appliances all located on one floor, available total height (H) shall be measured from the highest draft hood outlet or flue collar up to the level of the outlet of the common vent.
For multistory installations, available total height (H) for each segment of the system shall be the vertical distance between the highest draft hood outlet or flue collar entering that segment and the centerline of the next higher interconnection tee (see Figure B-13).
The size of the lowest connector and of the vertical vent leading to the lowest interconnection of a multistory system shall be in accordance with Table 504.2(1) or 504.2(2) for available total height (H) up to the lowest interconnection (see Figure B-14).
Where used in multistory systems, vertical common vents shall be Type B double wall and shall be installed with a listed vent cap.

Offsets in multistory common vent systems shall be limited to a single offset in each system, and systems with an offset shall comply with all of the following:

1. The offset angle shall not exceed 45 degrees (0.79 rad) from vertical.

2. The horizontal length of the offset shall not exceed 11/2 feet for each inch (18 mm per mm) of common vent diameter of the segment in which the offset is located.

3. For the segment of the common vertical vent containing the offset, the common vent capacity listed in the common venting tables shall be reduced by 20 percent (0.80 ´ maximum common vent capacity).

4. A multistory common vent shall not be reduced in size above the offset.

Where two or more appliances are connected to a vertical vent or chimney, the flow area of the largest section of vertical vent or chimney shall not exceed seven times the smallest listed appliance categorized vent areas, flue collar area or draft hood outlet area unless designed in accordance with approved engineering methods.
For appliances with more than one input rate, the minimum vent connector capacity (FAN Min) determined from the tables shall be less than the lowest appliance input rating, and the maximum vent connector capacity (FAN Max or NAT Max) determined from the tables shall be greater than the highest appliance input rating.
Listed, corrugated metallic chimney liner systems in masonry chimneys shall be sized by using Table 504.3(1) or 504.3(2) for Type B vents, with the maximum capacity reduced by 20 percent (0.80 ´ maximum capacity) and the minimum capacity as shown in Table 504.3(1) or 504.3(2). Corrugated metallic liner systems installed with bends or offsets shall have their maximum capacity further reduced in accordance with Sections 504.3.5 and 504.3.6. The 20-percent reduction for corrugated metallic chimney liner systems includes an allowance for one long-radius 90-degree (1.57 rad) turn at the bottom of the liner. Where double-wall connectors are required, tee and wye fittings used to connect to the common vent chimney liner shall be listed double-wall fittings. Connections between chimney liners and listed double-wall fittings shall be made with listed adapter fittings designed for such purpose.

Tables 504.3(1), 504.3(2), 504.3(3), 504.3(4) and 504.3(5) shall be used only for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. A Type B vent shall not be considered to be exposed to the outdoors where it passes through an unventilated enclosure or chase insulated to a value of not less than R8.

Tables 504.3(6) and 504.3(7) shall be used for clay-tile-lined exterior masonry chimneys, provided that all of the following conditions are met:

1. Vent connector is Type B double wall.

2. At least one appliance is draft hood equipped.

3. The combined appliance input rating is less than the maximum capacity given by Table 504.3(6a) for NAT+NAT or Table 504.3(7a) for FAN+NAT.

4. The input rating of each space-heating appliance is greater than the minimum input rating given by Table 504.3(6b) for NAT+NAT or Table 504.3(7b) for FAN+NAT.

5. The vent connector sizing is in accordance with Table 504.3(3).


Exception: Vents serving listed appliances installed in accordance with the appliance manufacturer’s installation instructions.

Vent connectors shall not be increased in size more than two sizes greater than the listed appliance categorized vent diameter, flue collar diameter or draft hood outlet diameter. Vent connectors for draft hood-equipped appliances shall not be smaller than the draft hood outlet diameter. Where a vent connector size(s) determined from the tables for a fan-assisted appliance(s) is smaller than the flue collar diameter, the use of the smaller size(s) shall be permitted provided that the installation complies with all of the following conditions:

1. Vent connectors for fan-assisted appliance flue collars 12 inches (305 mm) in diameter or smaller are not reduced by more than one table size [e.g., 12 inches to 10 inches (305 mm to 254 mm) is a one-size reduction] and those larger than 12 inches (305 mm) in diameter are not reduced more than two table sizes [e.g., 24 inches to 20 inches (610 mm to 508 mm) is a two-size reduction].

2. The fan-assisted appliance(s) is common vented with a draft-hood-equipped appliances(s).

3. The vent connector has a smooth interior wall.

All combinations of pipe sizes, single-wall and double-wall metal pipe shall be allowed within any connector run(s) or within the common vent, provided that all of the appropriate tables permit all of the desired sizes and types of pipe, as if they were used for the entire length of the subject connector or vent. Where single-wall and Type B double-wall metal pipes are used for vent connectors within the same venting system, the common vent must be sized using Table 504.3(2) or 504.3(4), as appropriate.
Draft hood conversion accessories for use with masonry chimneys venting listed Category I fan-assisted appliances shall be listed and installed in accordance with the manufacturer’s installation instructions for such listed accessories.
Where a table permits more than one diameter of pipe to be used for a connector or vent, all the permitted sizes shall be permitted to be used.
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between table entries (see Appendix B, Example 3).
Extrapolation beyond the table entries shall not be permitted.
For vent heights less than 6 feet (1829 mm) and greater than shown in the tables, engineering methods shall be used to calculate vent capacities.
The installation of direct-vent and integral vent appliances shall be in accordance with Section 503. Mechanical venting systems and exhaust hood venting systems shall be designed and installed in accordance with Section 503.

Where commercial cooking appliances are vented by means of the Type I or II kitchen exhaust hood system that serves such appliances, the exhaust system shall be fan powered and the appliances shall be interlocked with the exhaust hood system to prevent appliance operation when the exhaust hood system is not operating. The method of interlock between the exhaust hood system and the appliances equipped with standing pilot burner ignition systems shall not cause such pilots to be extinguished. Where a solenoid valve is installed in the gas piping as part of an interlock system, gas piping shall not be installed to bypass such valve. Dampers shall not be installed in the exhaust system.

Exception: An interlock between the cooking appliance(s) and the exhaust hood system shall not be required where heat sensors or other approved methods automatically activate the exhaust hood system when cooking operations occur.

Factory-built chimneys for building heating appliances producing flue gases having a temperature not greater than 1,000°F (538°C), measured at the entrance to the chimney, shall be listed and labeled in accordance with UL 103 and shall be installed and terminated in accordance with the manufacturer’s installation instructions.
Where factory-built chimneys are supported by structural members, such as joists and rafters, such members shall be designed to support the additional load.
Factory-built chimneys for medium-heat appliances producing flue gases having a temperature above 1,000°F (538°C), measured at the entrance to the chimney, shall be listed and labeled in accordance with UL 959 and shall be installed and terminated in accordance with the manufacturer’s installation instructions.
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