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ADOPTS WITHOUT AMENDMENTS:

International Fuel Gas Code 2021 (IFGC 2021)

Heads up: There are no amended sections in this chapter.
User note:
About this chapter: The majority of gas-fired appliances have their combustion products vented to the outdoors. Venting is by means of chimneys, vents, integral vents, direct-vents and power exhausters. Chapter 5 includes design, sizing and installation requirements for chimneys and vents and requirements for matching the appliance type to the appropriate venting system. Venting system termination location requirements are also addressed.
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 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 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 C315 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 501.8 and 503.2.1 through 503.2.4, all appliances shall be connected to venting systems.
The use of ventilating hoods and exhaust systems to vent appliances shall be limited to industrial appliances and appliances installed in commercial applications.
The flue gases from industrial-type appliances shall not be required to be vented to the outdoors where such gases are discharged into a large and well-ventilated industrial space.
Listed direct-vent appliances shall be installed in accordance with the manufacturer's instructions. Through-the-wall vent terminations for listed direct-vent appliances shall be in accordance with Section 503.8.
Appliances incorporating integral venting means shall be installed in accordance with Section 503.8.
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 in accordance with UL 378 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.
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 TYPE OF VENTING SYSTEM
Listed Category I appliances

Listed appliances equipped with draft hood

Appliances listed for use with Type B gas vent
Type B gas vent (Section 503.6)

Chimney (Section 503.5)

Single-wall metal pipe (Section 503.7)

Listed chimney lining system for gas venting (Section 503.5.3)

Special gas vent listed for these appliances (Section 503.4.2)
Listed vented wall furnaces Type B-W gas vent (Sections 503.6, 608)
Category II, Category III and Category IV appliances As specified or furnished by manufacturers of listed appliances (Sections 503.4.1, 503.4.2)
Incinerators In accordance with NFPA 82
Appliances that can be converted for use with solid fuel Chimney (Section 503.5)
Unlisted combination gas and oil-burning appliances Chimney (Section 503.5)
Listed combination gas and oil-burning appliances Type L vent (Section 503.6) or chimney (Section 503.5)
Combination gas and solid fuel-burning appliances Chimney (Section 503.5)
Appliances listed for use with chimneys only Chimney (Section 503.5)
Unlisted appliances Chimney (Section 503.5)
Decorative appliances in vented fireplaces Chimney
Gas-fired toilets Single-wall metal pipe (Section 626)
Direct-vent appliances See Section 503.2.3
Appliances with integral vent See Section 503.2.4
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. The plastic pipe venting materials shall be labeled in accordance with the product standards specified by the appliance manufacturer or shall be listed and labeled in accordance with UL 1738.
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer's instructions. Plastic pipe venting materials listed and labeled in accordance with UL 1738 shall be installed in accordance with the vent manufacturer's instructions. Where a primer is required, it shall be of a contrasting color.
Special gas vent shall be listed and labeled in accordance with UL 1738 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 503.5.11.
Factory-built chimneys shall be listed in accordance with UL 103. 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 an approved clay flue lining, a chimney lining system listed and labeled in accordance with UL 1777 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 503.6.4.
Chimneys for residential-type 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. The effective areas of the vent connector and chimney flue of a venting system serving a single appliance with a draft hood 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. The effective area of the chimney flue or a venting system serving two appliances with draft hoods 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 engineering methods.
  5. Other 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.
Cleanouts shall be examined and where they do not remain tightly closed when not in use, they shall be repaired or replaced.
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.
Where a single chimney flue serves a listed combination gas- and oil fuel-burning appliance, such flue shall be sized in accordance with appliance manufacturer's instructions.
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.
Where a factory-built chimney passes through insulated assemblies, an insulation shield constructed of steel having a thickness of not less than 0.0187 inch (0.475 mm) shall be installed to provide clearance between the chimney and the insulation material. The clearance shall be not less than the clearance to combustibles specified by the chimney manufacturer's installation instructions. Where chimneys pass through attic space, the shield shall terminate not less than 2 inches (51 mm) above the installation materials and shall be secured in place to prevent displacement.
Gas vents shall comply with Sections 503.6.1 through 503.6.14 (see Section 202, General Definitions).
Type B and BW gas vents shall be listed in accordance with UL 441. Vents for listed combination gas- and oil-burning appliances shall be listed in accordance with UL 641.
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 503.6.5.
  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 503.6.5
TERMINATION LOCATIONS FOR GAS VENTS WITH LISTED CAPS 12 INCHES OR LESS IN SIZE NOT LESS THAN 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 Sections 503.6.10.1 through 503.6.10.4 and the 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. Engineering methods.
Type B and L vents sized in accordance with Item 2 or 3 of Section 503.6.10.1 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 engineering methods.
Where a common vent is installed in a multistory installation to vent Category I appliances located on more than one floor level, the venting system shall be designed and installed in accordance with approved engineering methods. For the purpose of this section, crawl spaces, basements and attics shall be considered to be 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 not less than 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 single-wall metal pipe to combustible material shall be in accordance with Table 503.10.2.5. 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 be not greater than seven times the draft hood outlet area.
  3. 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 503.6.13.
The clearances for through-the-wall direct-vent and nondirect-vent terminals shall be in accordance with Table 503.8 and Figure 503.8.
Exception: The clearances in Table 503.8 shall not apply to the combustion air intake of a direct-vent appliance.
FIGURE 503.8
THROUGH-THE-WALL VENT TERMINAL CLEARANCES
 
TABLE 503.8
THROUGH-THE-WALL VENT TERMINAL CLEARANCE
FIGURE CLEARANCE CLEARANCE LOCATION MINIMUM CLEARANCE FOR DIRECT-VENT TERMINALS MINIMUM CLEARANCE FOR NONDIRECT-VENT TERMINALS
A Clearance above finished grade level, veranda, porch, deck, or balcony 12 inches
B Clearance to window or door that is openable 6 inches: Appliances ≤ 10,000 Btu/hr



9 inches: Appliances > 10,000 Btu/hr ≤ 50,000 Btu/hr



12 inches: Appliances > 50,000 Btu/hr ≤ 150,000 Btu/hr



Appliances > 150,000 Btu/hr, in accordance with the appliance manufacturer's instructions and not less than the clearances specified for nondirect-vent terminals in Row B
4 feet below or to side of opening or 1 foot above opening
C Clearance to nonopenable window None unless otherwise specified by the appliance manufacturer
D Vertical clearance to ventilated soffit located above the terminal within a horizontal distance of 2 feet from the center line of the terminal None unless otherwise specified by the appliance manufacturer
E Clearance to unventilated soffit None unless otherwise specified by the appliance manufacturer
F Clearance to outside corner of building None unless otherwise specified by the appliance manufacturer
G Clearance to inside corner of building None unless otherwise specified by the appliance manufacturer
H Clearance to each side of center line extended above regulator vent outlet 3 feet up to a height of 15 feet above the regulator vent outlet
I Clearance to service regulator vent outlet in all directions 3 feet for gas pressures up to 2 psi; 10 feet for gas pressures above 2 psi
J Clearance to nonmechanical air supply inlet to building and the combustion air inlet to any other appliance Same clearance as specified for Row B
K Clearance to a mechanical air supply inlet 10 feet horizontally from inlet or 3 feet above inlet
L Clearance above paved sidewalk or paved driveway located on public property 7 feet and shall not be located above public walkways or other areas where condensate or vapor can cause a nuisance or hazard
M Clearance to underside of veranda, porch deck, or balcony 12 inches where the area beneath the veranda, porch deck or balcony is open on not less than two sides. The vent terminal is prohibited in this location where only one side is open.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 Btu/hr = 0.293 W
Provisions shall be made to collect and dispose of condensate from venting systems serving Category II and IV appliances and noncategorized condensing appliances. Drains for condensate shall be installed in accordance with the appliance and vent manufacturer's instructions.
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.
  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 factory-built chimney section or steel pipe having resistance to heat and corrosion equivalent to that for the appropriate galvanized pipe as specified in Table 503.10.2.4. Factory-built chimney sections shall be joined together in accordance with the chimney manufacturer's instructions.
TABLE 503.10.2.4
MINIMUM THICKNESS FOR GALVANIZED STEEL VENT CONNECTORS FOR LOW-HEAT APPLIANCES
DIAMETER OF CONNECTOR (inches) MINIMUM THICKNESS (inch)
Less than 6
0.019
6 to less than 10
0.023
10 to 12 inclusive
0.029
14 to 16 inclusive
0.034
Over 16
0.056
For SI: 1 inch = 25.4 mm.
Vent connectors for medium-heat appliances 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 C64, Type F), or the equivalent.
  2. The lining shall be not less than 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 not less than 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. Where factory-built chimney sections are installed, they 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 MINIMUM THICKNESS (inch)
Diameter (inches) Area (square inches)
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 engineering methods.
Where a single appliance having more than one draft hood outlet or flue collar is installed, 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 engineering methods. 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 rise of not less than 12 inches (305 mm).
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 engineering methods.
As an alternative method applicable only where 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 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.
CLEARANCES FOR CONNECTORSa
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.
  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.
Where vent connectors are joined together, the connection shall be made with a tee or wye fitting.
A vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney not less than 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 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 and balancing baffles shall not be classified as manually operated dampers.
Balancing baffles shall be listed in accordance with UL 378 and shall be mechanically locked in the desired position before placing the appliance in operation.
An automatically operated vent damper shall be listed.
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 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 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 + 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.
FAN Max. The maximum input rating of a Category I fan-assisted appliance attached to a vent or connector.
FAN Min. The minimum input rating of a Category I fan-assisted appliance attached to a vent or connector.
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.
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.
NAT Max. The maximum input rating of a Category I draft-hood-equipped appliance attached to a vent or connector.
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
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
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
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.
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
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.
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
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 InternalArea 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)
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
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.
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