CODES

ADOPTS WITHOUT AMENDMENTS:

International Fuel Gas Code 2015 (IFGC 2015)

Copyright

Preface

Effective Use of the International Fuel Gas Code

Legislation

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

Chapter 7 Gaseous Hydrogen Systems

Chapter 8 Referenced Standards (IFGC/IFGS)

Appendix A Sizing and Capacities of Gas Piping (Ifgs)

Appendix B Sizing of Venting Systems Serving Appliances Equipped With Draft Hoods, Category I Appliances and Appliances Listed for Use With Type B Vents (Ifgs)

Appendix C Exit Terminals of Mechanical Draft and Direct-Vent Venting Systems (Ifgs)

Appendix D Recommended Procedure for Safety Inspection of an Existing Appliance Installation (Ifgs)

This chapter 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 foot (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 fluegas 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 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 that 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.
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 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 be not 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 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 not less than 4 inches (102 mm) above sole plates, below top plates and to each side of a stud, joist or rafter.
Appliance and equipment vent terminals shall be located such that doors cannot swing within 12 inches (305 mm) horizontally of the vent terminal. Door stops or closers shall not be installed to obtain this clearance.
The venting of appliances shall be in accordance with Sections 503.2 through 503.16.
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 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 installed in accordance with the manufacturer’s instructions and Section 503.8, Items 1 and 2.
Commercial-industrial-type incinerators shall be vented in accordance with NFPA 82.
Venting systems shall be designed and constructed so as to convey all flue and 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 instructions for both the appliance and the mechanical draft system.

2. Appliances 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 to 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.
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.

TABLE 503.4 TYPE OF VENTING SYSTEM TO BE USED

APPLIANCES
Where plastic piping is used to vent an appliance, the appliance shall be listed for use with such venting materials and the appliance manufacturer’s installation instructions shall identify the specific plastic piping material.
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s 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 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 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 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 residentialtype or low-heat appliances shall extend not less than 3 feet (914 mm) above the highest point where they pass through a roof of a building and not less than 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). Chimneys for medium-heat appliances shall extend not less than 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). Chimneys shall extend not less than 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 instructions.
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 fuelburning 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 not less than 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 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 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 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 instructions.
A Type B or L gas vent shall terminate not less than 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 not less than 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. The sizing of plastic pipe that is specified by the appliance manufacturer as a venting material for Category II, III and IV appliances shall be in accordance with the manufacturer’s instructions.
Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
A common 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.
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.
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.

2. The size of the connector for a segment is determined from the appliance input rating and available connector rise and shall be not 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 not less than 2 feet (610 mm) above the highest point where it passes through a roof of a building and not less than 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe.
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 not less than 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.
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 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 singlewall metal pipe to combustible material shall be in accordance with Table 503.10.5. The clearance from singlewall 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 be not 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 of 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 not less than 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 directvent appliances, shall terminate not less than 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 not less than 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 not less than 6 inches (152 mm) from any air opening into a building. 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 per hour (14.7 kW) shall have not less than a 12-inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located not less than 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 appliance and vent manufacturers' instructions.

5. Vent systems for Category IV appliances that terminate through an outside wall of a building and discharge flue gases perpendicular to the adjacent wall shall be located not less than 10 feet (3048 mm) horizontally from an operable opening in an adjacent building. This requirement shall not apply to vent terminals that are 2 feet (607 mm) or more above or 25 feet (7620 mm) or more below operable openings.
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, provisions 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 503.10.14.
A vent connector shall be used to connect an appliance to a gas vent, chimney or singlewall 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.

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 instructions.
A vent connector for a nonresidential, low-heat appliance shall be a factorybuilt 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 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 appliancewith 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 not less than 21/2inches (64mm) 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 not less than 41/2 inches (114mm) 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 togetherin accordance with the chimney manufacturer’s instructions.

TABLE 503.10.2.5 MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES

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 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.
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 not less than 1/4inch 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.
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; 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 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 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 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 fanassisted appliance attached to a vent or connector.

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

NAT Max. The maximum input rating of a Category I drafthood-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 504.2.17.

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)‒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
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
Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln 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)-continued TYPE B DOUBLE-WALL GAS VENT

Number of Appliances Single
Appliance Type Category I
Appliance Vent Connection Single-wall metal connector
HEGHT
(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
Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln Max Max Mln 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 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 Single3
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


(continued)

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 1003
-11°F or Lower Local 99% Winter Design Temperature: -11°F or Lower
Not recommended for any vent configurations

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.
Note: See Figure B-19 in Appendix B for a map showing local 99-percent winter design temperatures in the United States.
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 not less than 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 fanassisted 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 fanassisted 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. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Figure 503.6.4, and where vents terminate in accordance with Section 503.6.4, Item 2, the outdoor portion of the vent shall be enclosed as required by this section for vents not considered to be exposed to the outdoors or such venting system shall be engineered. 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).
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 instructions for such listed accessories.
Interpolation shall be permitted in calculating capacities for vent dimensions that fall between the table entries.
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.
Where the actual height of a vent falls between entries in the height column of the applicable table in Tables 504.2(1) through 504.2(6), either interpolation shall be used or the lower appliance input rating shown in the table entries shall be used for FAN MAX and NAT MAX column values and the higher appliance input rating shall be used for the FAN MIN column values.
The application of Tables 504.3(1) through 504.3(7) shall be subject to the requirements of Sections 504.3.1 through 504.3.28.

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)
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


(continued)

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 1,970 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
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 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


(continued)

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

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


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 1010
15 NA 152 233 334 467 611 781 1156
20 NA NA 250 368 508 668 858 1286
30 NA NA NA 404 564 747 969 1473
50 NA NA NA NA NA 831 1089 1692
100 NA NA NA NA NA NA NA 1921


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
orGreater
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 1600
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 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 1554


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 603 667 805
100 NA NA NA NA NA NA 955 1,003
-11°F or
Lower
Local 99% Winter Design Temperature:-11°F or Lower
Not recommended for any vent configurations

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

TABLE 504.3.2 MAXIMUM VENT CONNECTOR LENGTH

CONNECTOR DIAMETER
(inches)
CONNECTOR MAXIMUM
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 singlewall 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 notexceed 11/2feet for each inch (18 mm per mm) of common vent connector manifold diameter (D)
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 reducedsize 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.
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.
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. Where vents extend outdoors above the roof more than 5 feet (1524 mm) higher than required by Figure 503.6.4 and where vents terminate in accordance with Section 503.6.4, Item 2, the outdoor portion of the vent shall be enclosed as required by this section for vents not considered to be exposed to the outdoors or such venting system shall be engineered. 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(6a), 504.3(6b), 504.3(7a) and 504.3(7b) shall be used for clay-tile-lined exterior masonry chimneys, provided that all of the following conditions are met:

1. Vent connectors are Type B double wall.

2. Not less than 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).
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 (305mm) 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 onesize 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 appliance(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 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.
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.
Where the actual height of a vent falls between entries in the height column of the applicable table in Tables 504.3(1) through 504.3(7b), either interpolation shall be used or the lower appliance input rating shown in the table shall be used for FAN MAX and NAT MAX column values and the higher appliance input rating shall be used for the FAN MIN column values.
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 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 instructions.
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