CODES

ADOPTS WITH AMENDMENTS:

International Fuel Gas Code 2012 (IFGC 2012)

Copyright

Preface

Chapter 1 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

IFGC-IFGS Chapter 8 Referenced Standards

Appendix A (Ifgs) Sizing and Capacities of Gas Piping

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

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

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

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

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

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

  1. Clay flue lining complying with the requirements of ASTM C 315 or equivalent. Clay flue lining shall be installed in accordance with the International Building Code.
  2. Listed chimney lining systems complying with UL 1777.
  3. Other approved materials that will resist, without cracking, softening or corrosion, flue gases and condensate at temperatures up to 1,800°F (982°C).

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

  1. Flue lining systems complying with Section 501.12.
  2. Chimney lining systems listed and labeled for use with gas appliances with draft hoods and other Category I gas appliances listed and labeled for use with Type B vents.
The design, sizing and installation of vents for Category II, III and IV appliances shall be in accordance with the appliance manufacturer’s installation instructions.
Where an appliance is permanently disconnected from an existing chimney or vent, or where an appliance is connected to an existing chimney or vent during the process of a new installation, the chimney or vent shall comply with Sections 501.15.1 through 501.15.4.
The chimney or vent shall be resized as necessary to control flue gas condensation in the interior of the chimney or vent and to provide the appliance or appliances served with the required draft. For Category I appliances, the resizing shall be in accordance with Section 502.
The flue gas passageway shall be free of obstructions and combustible deposits and shall be cleaned if previously used for venting a solid or liquid fuel-burning appliance or fireplace. The flue liner, chimney inner wall or vent inner wall shall be continuous and shall be free of cracks, gaps, perforations or other damage or deterioration which would allow the escape of combustion products, including gases, moisture and creosote.
Masonry chimney flues shall be provided with a cleanout opening having a minimum height of 6 inches (152 mm). The upper edge of the opening shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The cleanout shall be provided with a tight-fitting, noncombustible cover.

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

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

Noncombustible fireblocking shall be provided in accordance with the International Building Code.

All vents, except as provided in Section 503.7, shall be listed and labeled. Type B and BW vents shall be tested in accordance with UL 441. Type L vents shall be tested in accordance with UL 641. Vents for Category II and III appliances shall be tested in accordance with UL 1738. Plastic vents for Category IV appliances shall not be required to be listed and labeled where such vents are as specified by the appliance manufacturer and are installed in accordance with the appliance manufacturer’s installation instructions.
Connectors shall be used to connect appliances to the vertical chimney or vent, except where the chimney or vent is attached directly to the appliance. Vent connector size, material, construction and installation shall be in accordance with Section 503.
The application of vents shall be in accordance with Table 503.4.
Where vents pass through insulated assemblies, an insulation shield constructed of steel having a minimum thickness of 0.0187 inch (0.4712 mm) (No. 26 gage) shall be installed to provide clearance between the vent and the insulation material. The clearance shall not be less than the clearance to combustibles specified by the vent manufacturer’s installation instructions. Where vents pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the insulation materials and shall be secured in place to prevent displacement. Insulation shields provided as part of a listed vent system shall be installed in accordance with the manufacturer’s installation instructions.
Vent systems shall be sized, installed and terminated in accordance with the vent and appliance manufacturer’s installation instructions and Section 503.
All portions of vents shall be adequately supported for the design and weight of the materials employed.
In concealed locations, where a vent is installed through holes or notches in studs, joists, rafters or similar members less than 11/2 inches (38 mm) from the nearest edge of the member, the vent shall be protected by shield plates. Protective steel shield plates having a minimum thickness of 0.0575 inch (1.463 mm) (No. 16 gage) shall cover the area of the vent where the member is notched or bored and shall extend a minimum of 4 inches (102 mm) above sole plates, below top plates and to each side of a stud, joist or rafter.
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 installation 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 into any portion of mechanical draft systems operating under positive pressure.
  5. Where a mechanical draft system is employed, provisions shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance.
  6. The exit terminals of mechanical draft systems shall be not less than 7 feet (2134 mm) above finished ground level where located adjacent to public walkways and shall be located as specified in Section 503.8, Items 1 and 2.
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications. Where automatically operated appliances, other than commercial cooking appliances, are vented through a ventilating hood or exhaust system equipped with a damper or with a power means of exhaust, provisions shall be made to allow the flow of gas to the main burners only when the damper is open to a position to properly vent the appliance and when the power means of exhaust is in operation.
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

APPLIANCESTYPE OF VENTING SYSTEM
Listed Category I appliances
Listed appliances equipped with draft hood
Appliances listed for use with Type B gas vent
Type B gas vent (Section 503.6)
Chimney (Section 503.5)
Single-wall metal pipe (Section 503.7)
Listed chimney lining system for gas venting (Section 503.5.3)
Special gas vent listed for these appliances (Section 503.4.2)
Listed vented wall furnacesType B-W gas vent (Sections 503.6, 608)
Category II appliancesAs specified or furnished by manufacturers of listed appliances
(Sections 503.4.1, 503.4.2)
Category III appliancesAs specified or furnished by manufacturers of listed appliances
(Sections 503.4.1, 503.4.2)
Category IV appliancesAs specified or furnished by manufacturers of listed appliances
(Sections 503.4.1, 503.4.2)
IncineratorsIn accordance with NFPA 82
Appliances that can be converted for use with solid fuelChimney (Section 503.5)
Unlisted combination gas and oil-burning appliancesChimney (Section 503.5)
Listed combination gas and oil-burning appliancesType L vent (Section 503.6) or chimney (Section 503.5)
Combination gas and solid fuel-burning appliancesChimney (Section 503.5)
Appliances listed for use with chimneys onlyChimney (Section 503.5)
Unlisted appliancesChimney (Section 503.5)
Decorative appliances in vented fireplacesChimney
Gas-fired toiletsSingle-wall metal pipe (Section 626)
Direct-vent appliancesSee Section 503.2.3
Appliances with integral ventSee Section 503.2.4
Plastic piping used for venting appliances listed for use with such venting materials shall be approved.
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions. Where a primer is required, it shall be of a contrasting color.
Special gas vent shall be listed and installed in accordance with the special gas vent manufacturer’s installation instructions.
Masonry, metal and factory-built chimneys shall comply with Sections 503.5.1 through 503.5.10.
Factory-built chimneys shall be installed in accordance with the manufacturer’s installation instructions. Factory-built chimneys used to vent appliances that operate at a positive vent pressure shall be listed for such application.
Metal chimneys shall be built and installed in accordance with NFPA 211.

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

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

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

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

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

  1. The provisions of Section 504.
  2. For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet, nor greater than seven times the draft hood outlet area.
  3. For sizing a chimney venting system connected to two appliances with draft hoods, the effective area of the chimney flue shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smallest draft hood outlet area.
  4. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
  5. Other approved engineering methods.
Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney passageway shall be examined to ascertain that it is clear and free of obstructions and it shall be cleaned if previously used for venting solid or liquid fuel-burning appliances or fireplaces.

Chimneys shall be lined in accordance with NFPA 211.

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

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

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

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

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

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

  1. Gas vents that are 12 inches (305 mm) or less in size and located not less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate above the roof in accordance with Figure 503.6.4.
  2. Gas vents that are over 12 inches (305 mm) in size or are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally.
  3. As provided for industrial appliances in Section 503.2.2.
  4. As provided for direct-vent systems in Section 503.2.3.
  5. As provided for appliances with integral vents in Section 503.2.4.
  6. As provided for mechanical draft systems in Section 503.3.3.
  7. As provided for ventilating hoods and exhaust systems in Section 503.3.4.

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

FIGURE 503.6.4

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

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

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

  1. The provisions of Section 504.
  2. For sizing an individual gas vent for a single, draft-hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet, nor greater than seven times the draft hood outlet area.
  3. For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smaller draft hood outlet area.
  4. Approved engineering practices.
Type B and L vents sized in accordance with Item 2 or 3 of Section 503.6.9.1 shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60-degree (1.04 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall be not greater than 75 percent of the vertical height of the vent.
The sizing of gas vents for Category II, III and IV appliances shall be in accordance with the appliance manufacturer’s instructions.
Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
A common vent shall be permitted in multistory installations to vent Category I appliances located on more than one floor level, provided that the venting system is designed and installed in accordance with approved engineering methods. For the purpose of this section, crawl spaces, basements and attics shall be considered as floor levels.
All appliances connected to the common vent shall be located in rooms separated from occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation and dilution air that is not supplied from an occupiable space.

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 not be smaller than the draft hood outlet or flue collar size.
  3. The size of the common vertical segment, and of the interconnection tee at the base of that segment, shall be based on the total appliance input rating entering that segment and its available total height.
Gas vents shall be supported and spaced in accordance with the manufacturer’s installation instructions.

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

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

Screws, rivets and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from an appliance draft hood outlet, a flue collar or a single-wall metal connector to a double-wall vent.
Single-wall metal pipe vents shall comply with Sections 503.7.1 through 503.7.13.
Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 inch (0.7 mm) thick, or other approved, noncombustible, corrosion-resistant material.
Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99-percent winter design temperature is below 32°F (0°C).
Single-wall metal pipe shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood outlet or flue collar. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). 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 at least 18 inches (457 mm) above and 6 inches (152 mm) below the roof with the annular space open at the bottom and closed only at the top. The thimble shall be sized in accordance with Section 503.7.7.
Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space or floor. The installation of a single-wall metal pipe through an exterior combustible wall shall comply with Section 503.7.7.

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

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

  1. For a draft-hood-equipped appliance, in accordance with Section 504.
  2. For a venting system for a single appliance with a draft hood, the areas of the connector and the pipe each shall be not less than the area of the appliance flue collar or draft hood outlet, whichever is smaller. The vent area shall not be greater than seven times the draft hood outlet area.
  3. Other approved engineering methods.
Any shaped single-wall metal pipe shall be permitted to be used, provided that its equivalent effective area is equal to the effective area of the round pipe for which it is substituted, and provided that the minimum internal dimension of the pipe is not less than 2 inches (51 mm).
The vent cap or a roof assembly shall have a venting capacity 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 at least 3 feet (914 mm) above any forced-air inlet located within 10 feet (3048 mm).

    Exceptions:

    1. This provision shall not apply to the combustion air intake of a direct-vent appliance.
    2. This provision shall not apply to the separation of the integral outdoor air inlet and flue gas discharge of listed outdoor appliances.
  2. A mechanical draft venting system, excluding direct-vent appliances, shall terminate at least 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from, or 1 foot (305 mm) above any door, operable window or gravity air inlet into any building. The bottom of the vent terminal shall be located at least 12 inches (305 mm) above finished ground level.
  3. The vent terminal of a direct-vent appliance with an input of 10,000 Btu per hour (3 kW) or less shall be located at least 6 inches (152 mm) from any air opening into a building, and such an appliance with an input over 10,000 Btu per hour (3 kW) but not over 50,000 Btu per hour (14.7 kW) shall be installed with a 9-inch (230 mm) vent termination clearance, and an appliance with an input over 50,000 Btu/h (14.7 kW) shall have at least a 12-inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located at least 12 inches (305 mm) above finished ground level.
  4. Through-the-wall vents for Category II and IV appliances and noncategorized condensing appliances shall not terminate over public walkways or over an area where condensate or vapor could create a nuisance or hazard or could be detrimental to the operation of regulators, relief valves or other equipment. Where local experience indicates that condensate is a problem with Category I and III appliances, this provision shall also apply. Drains for condensate shall be installed in accordance with the appliance and vent manufacturers’ instructions.
Provisions shall be made to collect and dispose of condensate from venting systems serving Category II and IV appliances and noncategorized condensing appliances in accordance with Section 503.8, Item 4. Where local experience indicates that condensation is a problem, provision shall be made to drain off and dispose of condensate from venting systems serving Category I and III appliances in accordance with Section 503.8, Item 4.
Vent connectors for Category I appliances shall comply with Sections 503.10.1 through 503.10.14.
A vent connector shall be used to connect an appliance to a gas vent, chimney or single-wall metal pipe, except where the gas vent, chimney or single-wall metal pipe is directly connected to the appliance.
Vent connectors shall be constructed in accordance with Sections 503.10.2.1 through 503.10.2.5.
A vent connector shall be made of noncombustible corrosion-resistant material capable of withstanding the vent gas temperature produced by the appliance and of sufficient thickness to withstand physical damage.

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

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

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

  1. Type B or L vent material;
  2. Galvanized sheet steel not less than 0.018 inch (0.46 mm) thick;
  3. Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 inch (0.69 mm) thick;
  4. Stainless steel sheet not less than 0.012 inch (0.31 mm) thick;
  5. Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Item 2, 3 or 4 above; or
  6. A listed vent connector.

Vent connectors shall not be covered with insulation.

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

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

TABLE 503.10.2.4

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

DIAMETER OF CONNECTOR
(inches)
MINIMUM THICKNESS
(inch)
Less than 60.019
6 to less than 100.023
10 to 12 inclusive0.029
14 to 16 inclusive0.034
Over 160.056

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 appliance with a vent gas temperature in excess of 1,000°F (538°C) measured at the entrance to the connector shall be lined with medium-duty fire brick (ASTM C 64, Type F), or the equivalent.
  2. The lining shall be at least 21/2 inches (64 mm) thick for a vent connector having a diameter or greatest cross-sectional dimension of 18 inches (457 mm) or less.
  3. The lining shall be at least 41/2 inches (114 mm) thick laid on the 41/2-inch (114 mm) bed for a vent connector having a diameter or greatest cross-sectional dimension greater than 18 inches (457 mm).
  4. Factory-built chimney sections, if employed, shall be joined together in accordance with the chimney manufacturer’s instructions.

TABLE 503.10.2.5

MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES

VENT CONNECTOR SIZE
Diameter
(inches)
Area
(square inches)
MINIMUM THICKNESS
(inch)
Up to 14Up to 1540.053
Over 14 to 16154 to 2010.067
Over 16 to 18201 to 2540.093
Over 18Larger than 2540.123

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

APPLIANCEMINIMUM 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 listedAs listed6 inchesAs listed
Residential boilers and furnaces with listed gas conversion burner and
with draft hood
6 inches6 inches9 inchesAs listed
Residential appliances listed for use with Type L ventsNot permittedAs listed9 inchesAs listed
Listed gas-fired toiletsNot permittedAs listedAs listedAs listed
Unlisted residential appliances with draft hoodNot permitted6 inches9 inchesAs listed
Residential and low-heat appliances other than aboveNot permitted9 inches18 inchesAs listed
Medium-heat appliancesNot permittedNot permitted36 inchesAs listed

For SI: 1 inch = 25.4 mm.

  1. 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 at least 1/4 inch per foot (21 mm/m).

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

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 installation instructions.
  2. Approved draft regulators and safety controls that are designed and installed in accordance with approved engineering methods.
  3. Listed heat reclaimers and automatically operated vent dampers installed in accordance with the manufacturer’s installation instructions.
  4. Approved economizers, heat reclaimers and recuperators installed in venting systems of appliances not required to be equipped with draft hoods, provided that the appliance manufacturer’s instructions cover the installation of such a device in the venting system and performance in accordance with Sections 503.3 and 503.3.1 is obtained.
  5. Vent dampers serving listed appliances installed in accordance with Sections 504.2.1 and 504.3.1 or other approved engineering methods.
Where vents, including those for direct-vent appliances, penetrate outside walls of buildings, the annular spaces around such penetrations shall be permanently sealed using approved materials to prevent entry of combustion products into the building.

The following definitions apply to the tables in this section.

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

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

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

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

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

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

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

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

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

The application of Tables 504.2(1) through 504.2(6) shall be subject to the requirements of Sections 504.2.1 through 504.2.17.

TABLE 504.2(1)

TYPE B DOUBLE-WALL GAS VENT

Number of AppliancesSingle
Appliance TypeCategory I
Appliance Vent ConnectionConnected directly to vent
HEIGHT
(H)
(feet)
LATERAL
(L)
(feet)
VENT DIAMETER—(D) inches
3456789
APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
600784601528602511410375205052428506983700897470
21351361897672715710532232157443212175342528563543370
42149343094643915310350227153663162117941927993536362
625463236916147149100592231497831020593413273110530354
8008450016594027615504152350583320078041501,006537
212574016109752517812028263180423652475048332260619418
523533832103714217111553255173703562378347331399607407
828493539986651164109642471658434722799463303117596396
100088530175100029516604472550631345084745001,096585
212614217118812319412926289195404022734853335557684457
523574032113774118712452280188683922638152234695671446
103051364110470541761156726717588376245104504330122651427
150094580191112032718705022850716390097052501,263682
211694815136932022615022339225384753164563341453815544
522654530130873921914249330217644633007662040390800529
10295941401218251206135643152088444528899600386116777507
153553374811276611951287630119898429275115580373134755491
20009761020211903492020540307077643001,05757501,384752
2107551141491001825016620377249335313464171147050917612
521714829143963824216047367241625193377369746086902599
10286444381338950229150623512288149932195675443112877576
153458404612484592171427333721794481308111654427129853557
2048523555116786920613484322206107464295125634410145830537
300010064021312803742200587336085347501,17365001,548855
2981561316611214283185184322802761339433826535421,072700
52177542816010836275176454212735860038569811524821,055688
1027705037150102482621715940526177580371917885071071,028668
153364NA44141965724916370389249905603571057654901241,002648
205658NA53132906623715480374237102542343119743473139977628
30NANANA73113NA88214NA104346219131507321149702444171929594
500010167021613403972320633363093251801,29770801,730952
2886611118312214320206154973142271544526975615331,276813
52082NA2717711935312200434873085570243865960605771,259798
102676NA35168114452991905647129873681426869355891011,230773
155970NA42158NA5428718066455288856624131009115721171,203747
20NANANA50149NA6327516976440278976424011138885561311,176722
30NANANA69131NA84250NA994102591236053761418445221611,125670
1000NANANA0218NA0407NA0665400099756001,41177001,9081,040
2NANANA10194NA12354NA1356637518831510211,155700251,536935
5NANANA26189NA33347NA4055736952820504601,141692711,519926
10NANANA33182NA43335NA5354236168801493801,118679941,492910
15NANANA40174NA50321NA6252835380782482931,0956661091,465895
20NANANA47166NA59311NA71513344907634711051,0736531221,438880
30NANANANANANA78290NA92483NA1157264491311,0296271491,387849
50NANANANANANANANANA147428NA1806514051979445752171,288787
HEIGHT
(H)
(feet)
LATERAL
(L)
(feet)
VENT DIAMETER—(D) inches
1012141618202224
APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
6001,12157001,64585002,2671,17002,9831,53003,8021,96004,7212,43005,7372,95006,8533,520
2756754551039826501381,3468901781,7691,1702252,2501,4802962,7821,8503603,3772,2204264,0302,670
41106684451479756401911,3388802421,7611,1603002,2421,4753902,7741,8354693,3702,2155554,0232,660
61286614351719676302191,3308702761,7531,1503412,2351,4704372,7671,8205233,3632,2106184,0172,650
8001,26166001,85897002,5711,32003,3991,74004,3332,22005,3872,75006,5553,36007,8384,010
271770515981,1247451301,5431,0201682,0301,3402122,5841,7002783,1962,1103363,8822,5604014,6343,050
51157585031541,1107331991,5281,0102512,0131,3303112,5631,6853983,1802,0904763,8632,5455624,6123,040
81377464901801,0977202311,5141,0002892,0001,3203542,5521,6704503,1632,0705373,8502,5306304,6023,030
10001,37772002,0361,06002,8251,45003,7421,92504,7822,45005,9553,05007,2543,71008,6824,450
268852560931,2448501241,7131,1301612,2561,4802022,8681,8902643,5562,3403194,3222,8403785,1533,390
51128395471491,2298291921,6961,1052432,2381,4613002,8491,8713823,5362,3184584,3012,8185405,1323,371
101428175251871,2047952381,6691,0802982,2091,4303642,8181,8404593,5042,2805464,2682,7806415,0993,340
15001,59684002,3801,24003,3231,72004,4232,27005,6782,90007,0993,62008,6654,410010,3935,300
2631,019675861,4959851142,0621,3501472,7191,7701863,4672,2602394,3042,8002905,2323,4103466,2514,080
51051,0036601401,4769671822,0411,3272292,6961,7482833,4422,2353554,2782,7774265,2043,3855016,2224,057
101359776351771,4469362272,0091,2892832,6591,7123463,4022,1934324,2342,7395105,1593,3435996,1754,019
151559536102021,4189052571,9761,2503182,6231,6753853,3632,1504794,1922,7005645,1153,3006656,1293,980
20001,75693002,6371,35003,7011,90004,9482,52006,3763,25007,9884,06009,7854,980011,7536,000
2591,150755811,6941,1001072,3431,5201393,0972,0001753,9552,5702204,9163,2002695,9833,9103217,1544,700
51011,1337381351,6741,0791742,3201,4982193,0711,9782703,9262,5443374,8853,1744035,9503,8804757,1194,662
101301,1057101721,6411,0452202,2821,4602733,0291,9403343,8802,5004134,8353,1304895,8963,8305737,0634,600
151501,0786881951,6091,0182482,2451,4253062,9881,9103723,8352,4654594,7863,0905415,8443,7956317,0074,575
201671,0526652171,5789902732,2101,3903352,9481,8804043,7912,4304954,7373,0505855,7923,7606896,9534,550
30001,9771,06003,0041,55004,2522,17005,7252,92007,4203,77009,3414,750011,4835,850013,8487,060
2541,351865742,0041,310982,7861,8001273,6962,3801594,7343,0501995,9003,8102417,1944,6502858,6175,600
5961,3328511271,9811,2891642,7591,7752063,6662,3502524,7013,0203125,8633,7833737,1554,6224398,5745,552
101251,3018291641,9441,2542092,7161,7332593,6172,3003164,6472,9703865,8033,7394567,0904,5745358,5055,471
151431,2728071871,9081,2202372,6741,6922923,5702,2503544,5942,9204315,7443,6955077,0264,5275908,4375,391
201601,2437842071,8731,1852602,6331,6503193,5232,2003844,5422,8704675,6863,6505486,9644,4806398,3705,310
301951,1897452461,8071,1303052,5551,5853693,4332,1304404,4422,7855405,5743,5656356,8424,3757398,2395,225
50002,2311,19503,4411,82504,9342,55006,7113,44008,7744,460011,1295,635013,7676,940016,6948,430
2411,6201,010662,4311,513863,4092,1251134,5542,8401415,8643,6701717,3394,6302098,9805,69525110,7886,860
5901,6009961182,4061,4951513,3802,1021914,5202,8132345,8263,6392837,2954,5973368,9335,65439410,7376,818
101181,5679721542,3661,4661963,3322,0642434,4642,7672955,7633,5853557,2244,5424198,8555,58549110,6526,749
151361,5369481772,3271,4372223,2852,0262744,4092,7213305,7013,5343967,1554,5114658,7795,54654210,5706,710
201511,5059241952,2881,4082443,2391,9873004,3562,6753615,6413,4814337,0864,4795068,7045,50658610,4886,670
301831,4468762322,2141,3492873,1501,9103474,2532,6314125,5233,4314946,9534,4215778,5575,44467210,3286,603
100002,4911,31003,9252,05005,7292,95007,9144,050010,4855,300013,4546,700016,8178,600020,57810,300
2301,9751,170443,0271,820724,3132,550955,8343,5001207,5914,6001389,5775,80016911,8037,20020414,2648,800
5821,9551,1591073,0021,8031364,2822,5311725,7973,4752087,5484,5662459,5285,76929311,7487,16234114,2048,756
101081,9231,1421422,9611,7751804,2312,5002235,7373,4342687,4784,5093189,4475,71737411,6587,10043614,1058,683
151261,8921,1241632,9201,7472064,1822,4692525,6783,3923047,4094,4513589,3675,66541811,5697,03748714,0078,610
201411,8611,1071812,8801,7192264,1332,4382775,6193,3513307,3414,3943879,2895,61345211,4826,97552313,9108,537
301701,8021,0712152,8031,6632654,0372,3753195,5053,2673787,2094,2794469,1365,50951411,3106,85059213,7208,391
502411,6881,0002922,6571,5503503,8562,2504155,2893,1004866,9564,0505728,8415,30065910,9796,60075213,3548,100

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 AppliancesSingle
Appliance TypeCategory I
Appliance Vent ConnectionSingle-wall metal connector
HEIGHT
(H)
(feet)
LATERAL
(L)
(feet)
VENT DIAMETER—(D) Inches
34567891012
APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMaxMlnMaxMax
603877455915185852491401263732041655222842116953692678944693711,1185695371.639849
239513660966685156104123231156159320213201423284251541368347673453498979648
4NANA33749263102152102146225152187313208237416277295533360409664443584971638
6NANA3183896011414799163220148207307203263409271327526352449656433638962627
803783505816493832731541234122341615803192067774142581,0025363601,2576585211,852967
23956395910875831761191212611791553632461974823212466174173397685134861,120743
5NANA3777102691071681141512521711933522352454703113056044044187545005981,104730
8NANA339095641221611071752431632233422252804583003445913924707404866651.089715
1003787535717499822931651204442541586283442028444492531,0935843511,3737185072,0311,057
23961415911780821931281192871941534002721935313542426814563328495594751,242848
552563976111761051851221482771861903882612415183442996674434098345445841,224825
10NANA3497100681321711121882611712373692412964973253636434234928085206881,194788
15036935756190111803251861164992831537133881959665232441.2596813361.5918384882,3741,237
23869475713693802251491153372241484733141876314132328125433191,0156734571.491983
551634475128861022161401443262171824592982316164002877955263929976575621,469963
10NANA3995116791282011311823082032284382842845923813497685014709666286641,433928
15NANANANANA721581861242202901922724182693345683674047424845409376017501,399894
20035966054200118783462011145373061497724281901,0535732381,3797503261,7519274732,6311,346
23774505614899782481651133752481445283441827084682279146113091,1467544431.6891.098
550684773140941002391581413632391785143342246924572798965963811,1267345471,6651,074
10NANA4193129861252231461773442242224913162776664373398665704571,0927026461,6261,037
15NANANANANA801552081362163252102644693013256404193938385495261,0606777301,5871,005
20NANANANANANA1861921262543061963094482853746164004488105265921,0286518081,550973
30034996353211127763722191105843341448494721841,1686472291,5428523121.9711,0564542,9961,545
237805655164111762811831094292791396103921758235332191,0696982961,3468634241,9991,308
549745272157106982711731364172711715953822158065212691,0496843661,3248465241,9711,283
10NANANA91144981222551681713972572135703672657775013271,0176624401,2878216201,9271,234
15NANANA115131NA1512391572083772422555473493127504813799856385071,2517947021,8841,205
20NANANANANANA181223NA2463572282985243333607234614339556155701,2167687801,8411,166
30NANANANANANANANANANANANA3894773054616704265418955747041,1477209371.7591,101
50033996651213133733942301056293611389285151761,2927042201,7249482952,2231,1894283,4321,818
236846153181121733182051044953121337124431689716132091,2738112801,6151,0074012,4261,509
54880NA70174117943081981314823051646964352049536022571,2527953471,5919914962,3961,490
10NANANA89160NA1182921861624612922036714202539235833131,2177654181,5519635892,3471,455
15NANANA112148NA1452751741994412802446464052998945623631,1837364811,5129346682,2991,421
20NANANANANANA176257NA2364202672856223893458665434151,1507085441,4739067412,2511,387
30NANANANANANANANANA315376NA373573NA4428095025211,0866496741,3998488922,1591,318
1000NANANA49214NA69403NA1006593951319915551661,4047652071,9001,0332732,4791,3003953,9122,042
2NANANA51192NA70351NA985633731258285081581,1526981961,5329332591,9701,1683713,0211,817
5NANANA67186NA90342NA1255513661568135011941,1346882401,5119213221,9451,1534602,9901,796
10NANANA85175NA113324NA1535323541917894862381,1046722931,4779023891.9051,1335472,9381,763
15NANANA132162NA138310NA1885113432307644732811,0756563421,4438844471,8651,1106182,8881,730
20NANANANANANA168295NA224487NA2707394583251,0466393911,4108645071,8251,0876902,8381,696
30NANANANANANA231264NA301448NA355685NA418988NA4911,3438246311,7471,0418342,7391,627
50NANANANANANANANANANANANA540584NA617866NA7111,205NA8951,591NA1,1382,5471,489

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 AppliancesSingle
Appliance TypeCategory I
Appliance Vent ConnectionType 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
34567891012
APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
62NANA28NANA52NANA86NANA130NANA180NANA247NANA320NANA401NANA581
5NANA25NANA49NANA82NANA117NANA165NANA231NANA298NANA376NANA561
82NANA29NANA55NANA93NANA145NANA198NANA266845903501007284461391,024651
5NANA26NANA52NANA88NANA134NANA183NANA247NANA3281497114232011,007640
8NANA24NANA48NANA83NANA127NANA175NANA239NANA318173695410231990623
102NANA31NANA61NANA103NANA162NANA2216851929882655388988104911361,144724
5NANA28NANA57NANA96NANA148NANA204NANA2771246383651467914661961,124712
10NANA25NANA50NANA87NANA139NANA191NANA2631556103471827624442401,093668
152NANA35NANA67NANA114NANA179534752506461333677779441929685621271,376841
5NANA35NANA62NANA107NANA164NANA231995943131187594161399465331861,352828
10NANA28NANA55NANA97NANA153NANA2161265652961487273941739125672291,315777
15NANANANANA48NANA89NANA141NANA201NANA2811716983751988804852591,280742
202NANA38NANA74NANA124NANA201515222746167837573867491871,0836271211,548953
5NANA36NANA68NANA116NANA18480503254956583501138454631331,0595971791,523933
10NANANANANA60NANA107NANA172NANA2371226273321438114401671,0225662211,482879
15NANANANANANANANA97NANA159NANA220NANA3141657804181919875412511,443840
20NANANANANANANANA83NANA148NANA206NANA2961867503972149555132771,406807
302NANA41NANA82NANA137NANA216475813035776242168985558811,2407171111,7931,112
5NANANANANA76NANA128NANA19875561281907413931069625261251,2166831691,7661,094
10NANANANANA67NANA115NANA184NANA2631157093731359275001581,1766482101,7211,025
15NANANANANANANANA107NANA171NANA243NANA3531568934761811,1396212391,679981
20NANANANANANANANA91NANA159NANA227NANA3321768604502031,1035922641,638940
30NANANANANANANANANANANANANANA188NANA288NANA4162491,0355553181,560877
502NANANANANA92NANA161NANA251NANA35151840477611,106633721,413812992,0801,243
5NANANANANANANANA151NANA230NANA32383819445981,0835961161,3877741552,0521,225
10NANANANANANANANA138NANA215NANA304NANA4241261,0475671471,3477331952,0061,147
15NANANANANANANANA127NANA199NANA282NANA4001461,0105391701,3077022221,9611,099
20NANANANANANANANANANANA185NANA264NANA3761659775111901,2696692461,9161,050
30NANANANANANANANANANANANANANANANANA327NANA4682331,1966232951,832984
Minimum Internal
Area of Chimney
(square inches)
1219283850637895132
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 AppliancesSingle
Appliance TypeCategory I
Appliance Vent ConnectionSingle-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
34567891012
APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
62NANA28NANA52NANA86NANA130NANA180NANA247NANA319NANA400NANA580
5NANA25NANA48NANA81NANA116NANA164NANA230NANA297NANA375NANA560
82NANA29NANA55NANA93NANA145NANA197NANA265NANA3493827254455491,021650
5NANA26NANA51NANA87NANA133NANA182NANA246NANA327NANA4226731,003638
8NANA23NANA47NANA82NANA126NANA174NANA237NANA317NANA408747985621
102NANA31NANA61NANA102NANA161NANA2202165182972716543873738084905361,142722
5NANA28NANA56NANA95NANA147NANA203NANA2763346353644597894656571,121710
10NANA24NANA49NANA86NANA137NANA189NANA261NANA3455477584417711,088665
152NANA35NANA67NANA113NANA1781664732492116113352647764403629655605201,373840
5NANA32NANA61NANA106NANA163NANA2302615913123257754144449425316371,348825
10NANA27NANA54NANA96NANA151NANA214NANA2943927223925319075047491,309774
15NANANANANA46NANA87NANA138NANA198NANA2784526923726068734818411,272738
202NANA38NANA73NANA123NANA2001635202732066753742588644902521,0796255081,544950
5NANA35NANA67NANA115NANA18380NA2522556553483178424614331,0555946231,518930
10NANANANANA59NANA105NANA170NANA2353126223303828064375171,0165627331,475875
15NANANANANANANANA95NANA156NANA217NANA3114427734145919795398231,434835
20NANANANANANANANA80NANA144NANA202NANA292NANA3926639445109111,394800
302NANA41NANA81NANA136NANA2151585783022007594202499825563401,2377154891,7891,110
5NANANANANA75NANA127NANA196NANA2792457373913069585244171,2106806001,7601,090
10NANANANANA66NANA113NANA182NANA2603007033703709204965001,1686447081,7131,020
15NANANANANANANANA105NANA168NANA240NANA3494288844715721,1286157981,668975
20NANANANANANANANA88NANA155NANA223NANA327NANA4456431,0895858831,624932
30NANANANANANANANANANANANANANA182NANA281NANA408NANA5441,0551,539865
502NANANANANA91NANA160NANA250NANA3501918374752381,1036313231,4088104632,0761,240
5NANANANANANANANA149NANA228NANA321NANA4422931,0785933981,3817705712,0441,220
10NANANANANANANANA136NANA212NANA301NANA4203551,0385624471,3377286741,9941,140
15NANANANANANANANA124NANA195NANA278NANA395NANA5335461,2946957611,9451,090
20NANANANANANANANANANANA180NANA258NANA370NANA5046161,2516608441,8981,040
30NANANANANA48NANANANANANANANANANANA318NANA458NANA6101,0091,805970
Minimum
Internal Area
of Chimney
(square inches)
1219283850637895132
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 AppliancesSingle
Appliance TypeDraft hood equipped
Appliance Vent ConnectionConnected directly to pipe or vent
HEIGHT (H)
(feet)
LATERAL (L)
(feet)
VENT DIAMETER—(D) inches
3456781012
MAXIMUM APPLIANCE INPUT RATING IN THOUSANDS OF BTU/H
603970116170232312500750
2315594141194260415620
5285188128177242390600
804276126185252340542815
23261102154210284451680
5295695141194264430648
10244986131180250406625
1004584138202279372606912
23567111168233311505760
53261104153215289480724
10275494143200274455700
15NA4684130186258432666
15049911512233124206841,040
23972122186260350570865
53567110170240325540825
103058103158223308514795
15NA5093144207291488760
20NANA82132195273466726
200531011632523424707701,190
24280136210286392641990
53874123192264364610945
103265115178246345571910
15NA55104163228326550870
20NANA91149214306525832
300561081832763845298781,370
244841482303204417301,140
5NA781372102964106941,080
10NA681251962743886561,050
15NANA1131772583666251,000
20NANA99163240344596960
30NANANANA192295540890
500NA1202103104435909801,550
2NA951712603704928201,290
5NANA1592343424747801,230
10NANA1462213184567301,190
15NANANA2002924077051,130
20NANANA1852763846701,080
30NANANANA2223306051,010

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 AppliancesSingle
Appliance TypeNAT
Appliance Vent ConnectionType 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)
12192838506378113
37°F or GreaterLocal 99% Winter Design Temperature: 37°F or Greater
600000000
800000000
1000000000
15NA0000000
20NANA12319024918400
30NANANANANA3933340
50NANANANANANANA579
27 to 36°FLocal 99% Winter Design Temperature: 27 to 36°F
60068116156180212266
80082127167187214263
1005197141183201225265
15NANANANA233253274305
20NANANANANA307330362
30NANANANANA419445485
50NANANANANANANA763
17 to 26°FLocal 99% Winter Design Temperature: 17 to 26°F
6NANANANANA215259349
8NANANANA197226264352
10NANANANA214245278358
15NANANANANA296331398
20NANANANANA352387457
30NANANANANANA507581
50NANANANANANANANA
5 to 16°FLocal 99% Winter Design Temperature: 5 to 16°F
6NANANANANANANA416
8NANANANANANA312423
10NANANANANA289331430
15NANANANANANA393485
20NANANANANANA450547
30NANANANANANANA682
50NANANANANANANA972
-10 to 4°FLocal 99% Winter Design Temperature: -10 to 4°F
6NANANANANANANA484
8NANANANANANANA494
10NANANANANANANA513
15NANANANANANANA586
20NANANANANANANA650
30NANANANANANANA805
50NANANANANANANA1,003
-11°F or LowerLocal 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 at least 10 feet (3048 mm).
  2. Vents for appliance draft hood outlets or flue collars 12 inches (305 mm) in diameter or smaller are not reduced more than one table size.
  3. Vents for appliance draft hood outlets or flue collars larger than 12 inches (305 mm) in diameter are not reduced more than two table sizes.
  4. The maximum capacity listed in the tables for a fan-assisted appliance is reduced by 10 percent (0.90 × maximum table capacity).
  5. The draft hood outlet is greater than 4 inches (102 mm) in diameter. Do not connect a 3-inch-diameter (76 mm) vent to a 4-inch-diameter (102 mm) draft hood outlet. This provision shall not apply to fan-assisted appliances.
Single-appliance venting configurations with zero (0) lateral lengths in Tables 504.2(1), 504.2(2) and 504.2(5) shall not have elbows in the venting system. Single-appliance venting configurations with lateral lengths include two 90-degree (1.57 rad) elbows. For each additional elbow up to and including 45 degrees (0.79 rad), the maximum capacity listed in the venting tables shall be reduced by 5 percent. For each additional elbow greater than 45 degrees (0.79 rad) up to and including 90 degrees (1.57 rad), the maximum capacity listed in the venting tables shall be reduced by 10 percent. Where multiple offsets occur in a vent, the total lateral length of all offsets combined shall not exceed that specified in Tables 504.2(1) through 504.2(5).
Zero (0) lateral (L) shall apply only to a straight vertical vent attached to a top outlet draft hood or flue collar.
Sea-level input ratings shall be used when determining maximum capacity for high altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high altitude installation.
For appliances with more than one input rate, the minimum vent capacity (FAN Min) determined from the tables shall be less than the lowest appliance input rating, and the maximum vent capacity (FAN Max/NAT Max) determined from the tables shall be greater than the highest appliance rating input.

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

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

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

Tables 504.2(1), 504.2(2), 504.2(3), 504.2(4) and 504.2(5) shall be used only for chimneys and vents not exposed to the outdoors below the roof line. A Type B vent or listed chimney lining system passing through an unused masonry chimney flue shall not be considered to be exposed to the outdoors. 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 installation 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 AppliancesTwo or more
Appliance TypeCategory I
Appliance Vent ConnectionType 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
345678910
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
612237263566464610672581641047722514292296185109376237128466289
22341313775554812186601831247925316895333220112424282131526345
32444353881624913296621991398227518997363248114463317134575386
8122402735724849114766417610984243148100320194118408248138507303
223443236805751128906619512986269175103356230121454294141564358
3244736378764531391016721014588290198105384258123492330143612402
10122432834785049123786518911389257154106341200125436257146542314
223473336865951136936720613491282182109374238128479305149596372
3245037379267521461046922015094303205111402268131515342152642417
15121503033895347142836422012088298163110389214134493273162609333
222533535966349153996623514291320193112419253137532323165658394
32455403610271511631116824816093339218115445286140565365167700444
20121543133995646157876224612586334171107436224131552285158681347
22257373410566481671046425914989354202110463265134587339161725414
32360423511074501761166627116891371228113486300137618383164764466
301206233311135945181936028813483391182103512238125649305151802372
22164393311870471901106229915885408215105535282129679360155840439
32266443412379481981246430917888423242108555317132706405158874494
501197136301336443216101573491457847719797627257120797330144984403
221734332137764522311959358172814902341006453061238203921481,014478
322754833141864622913461366194835022631036613431268424411511,043538
10011882372815866402621045344215073611204918102661121,0383411351,285417
21983443016179422671235544717875619242948223161151,0544051391,306494
32084503116389442721385745210978627272978343551181,0694551421,327555
COMMON VENT CAPACITY
VENT
HEIGHT
(H)
(feet)
45678910
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
6928165140116103204161147309248200404314260547434335672520410
81019073155129114224178163339275223444348290602480378740577465
101109779169141124243194178367299242477377315649522405800627495
1512511291195164144283228206427352280556444365753612465924733565
201361231022151831603142552294753943106214994058426885231,035826640
301521381182442101853612972665474593607205854709798086051,209975740
501671531342792442144213533106415474238547065501,1649777051,4511,188860
100175163NA311277NA489421NA7516584791,0258736251,4081,2158001,7841,502975
VENT CONNECTOR CAPACITY
VENT
HEIGHT
(H)
(feet)
CONNECTOR
RISE
(R)
(feet)
TYPE B DOUBLE-WALL VENT AND DIAMETER—(D) inches
12141618202224
APPLIANCE INPUT RATING LIMITS IN THOUSANDS OF BTU/H
FANNATFANNATFANNATFANNATFANNATFANNATFANNAT
MinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMaxMinMaxMax
621747644962231,046653