ADOPTS WITH AMENDMENTS:

UPC 2018

Heads up: There are no amended sections in this chapter.
The regulations of this chapter shall govern the construction, location, and installation of fuel-burning and other types of water heaters heating potable water, together with chimneys, vents, and their connectors. The minimum capacity for storage water heaters shall be in accordance with the first-hour rating listed in Table 501.1(2). No water heater shall be hereinafter installed that does not comply with the manufacturer's installation instructions and the type and model of each size thereof approved by the Authority Having Jurisdiction. A list of accepted water heater appliance standards is referenced in Table 501.1(1). Listed appliances shall be installed in accordance with the manufacturer's installation instructions. Unlisted water heaters shall be permitted in accordance with Section 504.3.2.

TABLE 501.1(1)
WATER HEATERS

TYPE STANDARD
Electric, Household UL 174
Oil-Fired Storage Tank UL 732
Gas, 75 000 Btu/h or less CSA Z21.10.1
Gas, Above 75 000 Btu/h CSA Z21.10.3
Electric, Commercial UL 1453
Solid Fuel UL 2523

For SI units: 1000 British thermal units per hour = 0.293 kW

TABLE 501.1(2)
FIRST HOUR RATING1

Number of Bathrooms 1 to 1.5 2 to 2.5 3 to 3.5
Number of Bedrooms 1 2 3 2 3 4 5 3 4 5 6
First Hour Rating,2 Gallons 38 49 49 49 62 62 74 62 74 74 74

For SI units: 1 gallon = 3.785 L

Notes:

1 The first-hour rating is found on the "Energy Guide" label.

2 Solar water heaters shall be sized to meet the appropriate first-hour rating as shown in the table.

It shall be unlawful for a person to install, remove, or replace or cause to be installed, removed, or replaced a water heater without first obtaining a permit from the Authority Having Jurisdiction to do so.
This inspection shall be made after chimneys, vents, or parts thereof, authorized by the permit, have been installed and before such vent or part thereof has been covered or concealed.
This inspection shall be made after work authorized by the permit has been installed. The Authority Having Jurisdiction will make such inspection as deemed necessary to be assured that the work has been installed in accordance with the intent of this code. No appliance or part thereof shall be covered or concealed until the same has been inspected and approved by the Authority Having Jurisdiction.
Water heater installations in bedrooms and bathrooms shall comply with one of the following [NFPA 54:10.27.1]:
  1. Fuel-burning water heaters shall be permitted to be installed in a closet located in the bedroom or bathroom provided the closet is equipped with a listed, gasketed door assembly and a listed self-closing device. The self-closing door assembly shall meet the requirements of Section 504.1.1. The door assembly shall be installed with a threshold and bottom door seal and shall meet the requirements of Section 504.1.2. Combustion air for such installations shall be obtained from the outdoors in accordance with Section 506.4. The closet shall be for the exclusive use of the water heater.
  2. Water heater shall be of the direct vent type. [NFPA 54: 10.27.1(2)]
Self-closing doors shall swing easily and freely, and shall be equipped with a self-closing device to cause the door to close and latch each time it is opened. The closing mechanism shall not have a hold-open feature.
Gasketing on gasketed doors or frames shall be furnished in accordance with the published listings of the door, frame, or gasketing material manufacturer.

Exception: Where acceptable to the Authority Having Jurisdiction, gasketing of non-combustible or limited-combustible material shall be permitted to be applied to the frame, provided closing and latching of the door are not inhibited.

Water heaters of other than the direct-vent type shall be located as close as practical to the chimney or gas vent.
The clearance requirements for water heaters shall comply with Section 504.3.1 or Section 504.3.2.
The clearances shall not be such as to interfere with combustion air, draft hood clearance and relief, and accessibility for servicing. Listed water heaters shall be installed in accordance with their listings and the manufacturer's installation instructions.
Unlisted water heaters shall be installed with a clearance of 12 inches (305 mm) on all sides and rear. Combustible floors under unlisted water heaters shall be protected in an approved manner. [NFPA 54:10.27.2.2]
A water heater installation shall be provided with overpressure protection using an approved, listed device installed in accordance with the terms of its listing and the manufacturer's installation instructions.
A water heater installation or a hot water storage vessel installation shall be provided with overtemperature protection by means of an approved, listed device installed in accordance with the terms of its listing and the manufacturer's installation instructions.
Temperature, pressure, and vacuum relief devices or combinations thereof, and automatic gas shutoff devices shall be installed in accordance with the terms of their listings and the manufacturer's installation instructions. A shut-off valve shall not be placed between the relief valve and the water heater or on discharge pipes between such valves and the atmosphere. The hourly British thermal units (Btu) (kW•h) discharge capacity or the rated steam relief capacity of the device shall be not less than the input rating of the water heater. Discharge piping shall be installed in accordance with Section 608.5.
Water heaters deriving heat from fuels or types of energy other than gas shall comply with the standards referenced in Table 501.1(1), Section 505.3, or Section 505.4. Vents or chimneys for such appliances shall be of approved types. An adequate supply of air for combustion and for adequate ventilation of heater rooms or compartments shall be provided. Each such appliance shall be installed in a location approved by the Authority Having Jurisdiction and local and state fire-prevention agencies.
Storage-type water heaters and hot water boilers deriving heat from fuels or types of energy other than gas, shall be provided with, in addition to the primary temperature controls, an over-temperature safety protection device that complies with and is installed in accordance with nationally recognized applicable standards for such devices and a combination temperature and pressure-relief valve.
Oil-fired water heaters shall be installed in accordance with NFPA 31.
Indirect-fired water heaters shall be in accordance with the applicable sections of the ASME Boiler and Pressure Vessel Code or shall comply with one of the other applicable standards shown in Table 501.1(1). Each water heater shall bear a label in accordance with ASME requirements, or an approved testing agency, certifying and attesting that such an appliance has been tested, inspected and meets the requirements of the applicable standards or code.
An indirect-fired water heater that incorporates a single-wall heat exchanger shall be in accordance with the following requirements:
  1. The heat transfer medium shall be either potable water or contain fluids recognized as safe by the Food and Drug Administration (FDA) as food grade.
  2. Bear a label with the word "Caution," followed by the following statements:
    1. The heat-transfer medium shall be potable water or other nontoxic fluid recognized as safe by the FDA.
    2. The maximum operating pressure of the heat exchanger shall not exceed the maximum operating pressure of the potable water supply.
  3. The word "Caution" and the statements in letters shall have an uppercase height of not less than 0.120 of an inch (3.048 mm). The vertical spacing between lines of type shall be not less than 0.046 of an inch (1.168 mm). Lowercase letters shall be compatible with the uppercase letter size specification.
Air for combustion, ventilation, and dilution of flue gases for appliances installed in buildings shall be obtained by application of one of the methods covered in Section 506.2 through Section 506.7.3. Where the requirements of Section 506.2 are not met, outdoor air shall be introduced in accordance with methods covered in Section 506.4 through Section 506.7.3.

Exception: This provision shall not apply to direct-vent appliances. [NFPA 54:9.3.1.1]

Appliances of other than natural draft design appliances not designated as Category I vented appliances, and appliances equipped with power burners shall be provided with combustion, ventilation, and dilution air in accordance with the appliance manufacturer's instructions. [NFPA 54:9.3.1.2]
Where used, a draft hood or a barometric draft regulator shall be installed in the same room or enclosure as the appliance served so as to prevent a difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:9.3.1.4]
Where exhaust fans, clothes dryers, and kitchen ventilation systems interfere with the operation of appliances, makeup air shall be provided. [NFPA 54:9.3.1.5]
The required volume of indoor air shall be determined in accordance with the method in Section 506.2.1 or Section 506.2.2, except that where the air infiltration rate is known to be less than 0.40 ACH (air change per hour), the method in Section 506.2.2 shall be used. The total required volume shall be the sum of the required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section 506.3 are considered a part of the required volume. [NFPA 54:9.3.2]
The required volume shall be not less than 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m3/kW). [NFPA 54:9.3.2.1]
Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows: [NFPA 54:9.3.2.2]:
  1. For appliances other than fan-assisted, calculate using the following Equation 506.2.2(1). [NFPA 54:9.3.2.2(1)]

    [Equation 506.2.2(1)]

    Required volume other ≥ (21 ft3/ACH) × (Iother/1000 Btu/h)

  2. For fan-assisted appliances, calculate using the following Equation 506.2.2(2). [NFPA 54:9.3.2.2(2)]

    [Equation 506.2.2(2)]

    Required volume fan ≥ (15 ft3/ACH) × (Ifan/1000 Btu/h)

    Where:

    Iother = All appliances other than fan-assisted input in (Btu/h)
    Ifan = Fan-assisted appliance input in (Btu/h)
    ACH = Air change per hour (percent of volume of space exchanged per hour, expressed as a decimal)

    For SI units: 1 cubic foot = 0.0283 m3, 1000 British thermal units per hour = 0.293 kW

  3. For purposes of these calculations, an infiltration rate greater than 0.60 ACH shall not be used in the equations in Section 506.2.2(1) and Section 506.2.2(2). [NFPA 54:9.3.2.2(3)]
Openings used to connect indoor spaces shall be sized and located in accordance with the following:
  1. Each opening shall have a free area of not less than 1 square inch per 1000 Btu/h (0.002 m2/kW) of the total input rating of appliances in the space, but not less than 100 square inches (0.065 m2). One opening shall commence within 12 inches (305 mm) of the top of the enclosure, and one opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 506.3). The dimension of air openings shall be not less than 3 inches (76 mm).
  2. The volumes of spaces in different stories shall be considered as communicating spaces where such spaces are connected by one or more openings in doors or floors having a total free area of not less than 2 square inches per 1000 Btu/h (0.004 m2/kW) of total input rating of appliances. [NFPA 54:9.3.2.3]

FIGURE 506.3
COMBUSTION AIR FROM ADJACENT INDOOR SPACES THROUGH INDOOR COMBUSTION AIR OPENINGS [NFPA 54: FIGURE A.9.3.2.3(1)]

Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with methods in Section 506.4.1 or Section 506.4.2. The dimension of air openings shall be not less than 3 inches (76 mm). [NFPA 54:9.3.3]
Two permanent openings, one commencing within 12 inches (305 mm) of the top of the enclosure and one commencing within 12 inches (305 mm) of the bottom of the enclosure, shall be provided. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors, as follows:
  1. Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4000 Btu/h (0.0005 m2/kW) of total input rating of all appliances in the enclosure. [See Figure 506.4.1(1) and Figure 506.4.1(2)]
  2. Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of 1 square inch per 2000 Btu/h (0.001 m2/kW) of total input rating of all appliances in the enclosure. [See Figure 506.4.1(3)] [NFPA 54:9.3.3.1]

FIGURE 506.4.1(1)
COMBUSTION AIR FROM OUTDOORS INLET AIR FROM VENTILATED CRAWL SPACE AND OUTLET AIR TO VENTILATED ATTIC [NFPA 54: FIGURE A.9.3.3.1(1)(a)]

For SI units: 1 foot = 304.8 mm

FIGURE 506.4.1(2)
COMBUSTION AIR FROM OUTDOORS THROUGH VENTILATED ATTIC [NFPA 54: FIGURE A.9.3.3.1(1)(b)]

FIGURE 506.4.1(3)
COMBUSTION AIR FROM OUTDOORS THROUGH HORIZONTAL DUCTS [NFPA 54: FIGURE A.9.3.3.1(2)]

One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of at least 1 inch (25.4 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or shall communicate through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors (see Figure 506.4.2) and shall have a minimum free area of the following:
  1. One square inch per 3000 Btu/h (0.0007 m2/kW) of the total input rating of all appliances located in the enclosure.
  2. Not less than the sum of the areas of all vent connectors in the space. [NFPA 54:9.3.3.2]

FIGURE 506.4.2
COMBUSTION AIR FROM OUTDOORS THROUGH
SINGLE COMBUSTION AIR OPENING
[NFPA 54: FIGURE A.9.3.3.2]

The use of a combination of indoor and outdoor combustion air shall be in accordance with Section 506.5.1 through Section 506.5.3. [NFPA 54:9.3.4] (See Appendix J for example calculations).
Where used, openings connecting the interior spaces shall be in accordance with Section 506.3. [NFPA 54:9.3.4(1)]
Outdoor openings shall be located in accordance with Section 506.4. [NFPA 54:9.3.4(2)]
The outdoor opening(s) size shall be calculated in accordance with the following:
  1. The ratio of interior spaces shall be the volume of the communicating spaces divided by the required volume.
  2. The outdoor size reduction factor shall be one minus the ratio of interior spaces.
  3. The size of outdoor openings shall be not less than the full size of outdoor openings calculated in accordance with Section 506.4, multiplied by the reduction factor. The dimension of air openings shall be not less than 3 inches (76 mm). [NFPA 54:9.3.4(3)]
Engineered combustion air installations shall provide an adequate supply of combustion, ventilation, and dilution air and shall be approved by the Authority Having Jurisdiction. [NFPA 54:9.3.5]
Where combustion air is provided by a mechanical air supply system, the combustion air shall be supplied from outdoors at the minimum rate of 0.35 cubic feet per minute per 1000 Btu/h [0.034 (m3/min)/kW] for appliances located within the space. [NFPA 54:9.3.6]
Where exhaust fans are installed, additional air shall be provided to replace the exhausted air. [NFPA 54:9.3.6.1]
Each of the appliances served shall be interlocked to the mechanical air supply system to prevent main burner operation where the mechanical air supply system is not in operation. [NFPA 54:9.3.6.2]
Where combustion air is provided by the building's mechanical ventilation system, the system shall provide the specified combustion air rate in addition to the required ventilation air. [NFPA 54:9.3.6.3]
The required size of openings for combustion, ventilation, and dilution air shall be based on the net free area of each opening. Where the free area through a design of louver, grille, or screen is known, it shall be used in calculating the size opening required to provide the free area specified. Where the louver and grille design and free area are not known, it shall be assumed that wood louvers have 25 percent free area and metal louvers and grilles have 75 percent free area. Nonmotorized louvers and grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]
Screens shall be not less than 1/4 of an inch (6.4 mm) mesh. [NFPA 54:9.3.7.2]
Motorized louvers shall be interlocked with the appliance so they are proven in the full open position prior to main burner ignition and during main burner operation. Means shall be provided to prevent the main burner from igniting should the louver fail to open during burner startup and to shut down the main burner if the louvers close during burner operation. [NFPA 54:9.3.7.3]
Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:
  1. Ducts shall be constructed of galvanized steel or a material having equivalent corrosion resistance, strength, and rigidity.

    Exception: Within dwelling units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:9.3.8.1]

  2. Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances. [NFPA 54:9.3.8.2]
  3. Ducts shall serve a single space. [NFPA 54:9.3.8.3]
  4. Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air. [NFPA 54:9.3.8.4]
  5. Ducts shall not be screened where terminating in an attic space. [NFPA 54:9.3.8.5]
  6. Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located at least 12 inches (305 mm) vertically from the adjoining finished ground level. [NFPA 54:9.3.8.8]
  7. Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air. [NFPA 54:9.3.8.6]
  8. 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.

    Exception: Direct-vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer's installation instructions. [NFPA 54:9.3.8.7]

The Authority Having Jurisdiction shall have the authority to require the use of an approved dielectric insulator on the water piping connections of water heaters and related water heating appliances.
In seismic design categories C, D, E, and F, water heaters shall be anchored or strapped to resist horizontal displacement due to earthquake motion. Strapping shall be at points within the upper one-third and lower one-third of its vertical dimensions. At the lower point, a distance of not less than 4 inches (102 mm) shall be maintained from the controls with the strapping.
Appliances and equipment shall be furnished either with load-distributing bases or with a sufficient number of supports to prevent damage to either the building structure or the appliance and the equipment. [NFPA 54:9.1.8.1]
At the locations selected for installation of appliances and equipment, the dynamic and static load carrying capacities of the building structure shall be checked to determine whether they are adequate to carry the additional loads. The appliances and equipment shall be supported and shall be connected to the piping so as not to exert undue stress on the connections. [NFPA 54:9.1.8.2]
A water heater supported from the earth shall rest on level concrete or other approved base extending not less than 3 inches (76 mm) above the adjoining ground level.
Where a water heater is located in an attic, in or on an attic ceiling assembly, floor-ceiling assembly, or floor-subfloor assembly where damage results from a leaking water heater, a watertight pan of corrosion-resistant materials shall be installed beneath the water heater with not less than 3/4 of an inch (20 mm) diameter drain to an approved location. Such pan shall be not less than 11/2 inches (38 mm) in depth.
When additional or replacement appliances or equipment is installed or an appliance is converted to gas from another fuel, the location in which the appliances or equipment is to be operated shall be checked to verify the following:
  1. Air for combustion and ventilation is provided where required, in accordance with the provisions of Section 506.0. Where existing facilities are not adequate, they shall be upgraded to meet Section 506.0 specifications.
  2. The installation components and appliances meet the clearances to combustible material provisions of Section 507.27. It shall be determined that the installation and operation of the additional or replacement appliances do not render the remaining appliances unsafe for continued operation.
  3. The venting system is constructed and sized in accordance with the provisions of Section 509.0. Where the existing venting system is not adequate, it shall be upgraded to comply with Section 509.0. [NFPA 54:9.1.2]
The appliance shall be connected to the fuel gas for which it was designed. No attempt shall be made to convert the appliance from the gas specified on the rating plate for use with a different gas without consulting the installation instructions, the serving gas supplier, or the appliance manufacturer for complete instructions. [NFPA 54:9.1.3]
Unlisted appliances for use with undiluted liquefied petroleum gases and installed indoors, except attended laboratory equipment, shall be equipped with safety shutoff devices of the complete shutoff type. [NFPA 54:9.1.4]
Where air or oxygen under pressure 'is used in connection with the gas supply, effective means such as a backpressure regulator and relief valve shall be provided to prevent air or oxygen from passing back into the gas piping. Where oxygen is used, installation shall be in accordance with NFPA 51. [NFPA 54:9.1.5]
Nondirect-vent appliances installed in beauty shops, barber shops, or other facilities where chemicals that generate corrosive or flammable products such as aerosol sprays are routinely used shall be located in a mechanical room separate or partitioned off from other areas with provisions for combustion and dilution air from outdoors. Direct-vent appliances in such facilities shall be in accordance with the appliance manufacturer's installation instructions. [NFPA 54:9.1.6.2]
In addition to air needed for combustion in commercial or industrial processes, process air shall be provided as required for cooling of appliances, equipment, or material; for controlling dew point, heating, drying, oxidation, dilution, safety exhaust, odor control, air for compressors; and for comfort and proper working conditions for personnel. [NFPA 54:9.1.7]
Appliances shall not be installed in areas where the open use, handling, or dispensing of flammable liquids occurs, unless the design, operation, or installation reduces the potential of ignition of the flammable vapors. Appliances installed in compliance with Section 507.13 through Section 507.15 shall be considered to comply with the intent of this provision. [NFPA 54:9.1.9]
Appliances in residential garages and in adjacent spaces that open to the garage and are not part of the living space of a dwelling unit shall be installed so that all burners and burner-ignition devices are located not less than 18 inches (457 mm) above the floor unless listed as flammable vapor ignition resistant. [NFPA 54:9.1.10.1]
Appliances installed in garages, warehouses, or other areas subject to mechanical damage shall be guarded against such damage by being installed behind protective barriers or by being elevated or located out of the normal path of vehicles.
Where appliances are installed in a separate, enclosed space having access only from outside of the garage, such appliances shall be permitted to be installed at floor level, providing the required combustion air is taken from the exterior of the garage. [NFPA 54:9.1.10.3]
Appliances installed in commercial garages shall comply with Section 507.14.1 and Section 507.14.2.
Appliances installed in enclosed, basement, and underground parking structures shall be installed in accordance with NFPA 88A. [NFPA 54:9.1.11.1]
Appliances installed in repair garages shall be installed in accordance with NFPA 30A. [NFPA 54:9.1.11.2]
Heaters in aircraft hangars shall be installed in accordance with NFPA 409. [NFPA 54:9.1.12]
Appliances shall be vented in accordance with the provisions of Section 509.0. [NFPA 54:9.1.14]
No device or attachment shall be installed on an appliance that is capable of impairing the combustion of gas. [NFPA 54:9.1.15]
When additional appliances are being connected to a gas piping system, the existing piping shall be checked to determine whether it has adequate capacity. Where the capacity is inadequate, the existing system shall be enlarged as necessary, or separate gas piping of adequate capacity shall be run from the point of delivery to the appliance. [NFPA 54:9.1.16]
Appliances shall be supported and connected to the piping so as not to exert undue strain on the connections. [NFPA 54:9.1.17]
Where the gas supply pressure is higher than that at which the appliance is designed to operate or varies beyond the design pressure limits of the appliance, a gas appliance pressure regulator shall be installed. [NFPA 54:9.1.18]
Venting of gas appliance pressure regulators shall comply with the following requirements:
  1. Appliance pressure regulators requiring access to the atmosphere for successful operation shall be equipped with vent piping leading outdoors or, if the regulator vent is an integral part of the appliance, into the combustion chamber adjacent to a continuous pilot, unless constructed or equipped with a vent limiting means to limit the escape of gas from the vent opening in the event of diaphragm failure.
  2. Vent limiting means shall be employed on listed appliance pressure regulators only.
  3. In the case of vents leading outdoors, means shall be employed to prevent water from entering this piping and also to prevent blockage of vents by insects and foreign matter.
  4. Under no circumstances shall a regulator be vented to the appliance flue or exhaust system.
  5. In the case of vents entering the combustion chamber, the vent shall be located so the escaping gas is readily ignited by the pilot and the heat liberated thereby does not adversely affect the normal operation of the safety shutoff system. The terminus of the vent shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the vent piping shall be determined.
  6. A vent line(s) from an appliance pressure regulator and a bleed line(s) from a diaphragm-type valve shall not be connected to a common manifold terminating in a combustion chamber. Vent lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.19]
Bleed lines shall comply with the following requirements:
  1. Diaphragm-type valves shall be equipped to convey bleed gas to the outdoors or into the combustion chamber adjacent to a continuous pilot.
  2. In the case of bleed lines leading outdoors, means shall be employed to prevent water from entering this piping and also to prevent blockage of vents by insects and foreign matter.
  3. Bleed lines shall not terminate in the appliance flue or exhaust system.
  4. In the case of bleed lines entering the combustion chamber, the bleed line shall be located so the bleed gas is readily ignited by the pilot and the heat liberated thereby does not adversely affect the normal operation of the safety shutoff system. The terminus of the bleed line shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the bleed line piping shall be determined.
  5. A bleed line(s) from a diaphragm-type valve and a vent line(s) from an appliance pressure regulator shall not be connected to a common manifold terminating in a combustion chamber. Bleed lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.20]
A combination of appliances, equipment, attachments, or devices used together in a manner shall be in accordance with the standards that apply to the individual appliance and equipment. [NFPA 54:9.1.21]
The installing agency shall comply with the appliance and equipment manufacturer's installation instructions in completing an installation. The installing agency shall leave the manufacturer's installation, operating, and maintenance instructions in a location on the premises where they will be readily available for reference and guidance for the Authority Having Jurisdiction, service personnel, and the owner or operator. [NFPA 54:9.1.22]
Appliances not listed for outdoor installation but installed outdoors shall be provided with protection to the degree that the environment requires. Appliances listed for outdoor installation shall be permitted to be installed without protection in accordance with the provisions of its listing and the manufacturer's installation instructions.
Appliances shall be located with respect to building construction and other equipment so as to permit access to the appliance. Sufficient clearance shall be maintained to permit cleaning of heating surfaces; the replacement of filters, blowers, motors, burners, controls, and vent connections; the lubrication of moving parts where necessary; the adjustment and cleaning of burners and pilots; and the proper functioning of explosion vents, where provided. For attic installation, the passageway and servicing area adjacent to the appliance shall be floored. [NFPA 54:9.2.1]
Appliances and their vent connectors shall be installed with clearances from combustible material so their operation does not create a hazard to persons or property. Minimum clearances between combustible walls and the back and sides of various conventional types of appliances and their vent connectors are specified in Section 509.0. [NFPA 54:9.2.2]
Appliances on roofs shall be designed or enclosed so as to withstand climatic conditions in the area in which they are installed. Where enclosures are provided, each enclosure shall permit easy entry and movement, shall be of reasonable height, and shall have at least a 30 inch (762 mm) clearance between the entire service access panel(s) of the appliance, and the wall of the enclosure. [NFPA 54:9.4.1.1]
Roofs on which appliances are to be installed shall be capable of supporting the additional load or shall be reinforced to support the additional load. [NFPA 54:9.4.1.2]
Access locks, screws, and bolts shall be of corrosion-resistant material. [NFPA 54:9.4.1.3]
Appliances shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:9.4.2.1]
Appliances shall be installed on a well-drained surface of the roof. At least 6 feet (1829 mm) of clearance shall be available between any part of the appliance, and the edge of a roof or similar hazard, or rigidly fixed rails, guards, parapets, or other building structures at least 42 inches (1067 mm) in height shall be provided on the exposed side. [NFPA 54:9.4.2.2]
All appliances requiring an external source of electrical power for its operation shall be provided with the following:
  1. A readily accessible electrical disconnecting means within sight of the appliance that completely deenergizes the appliance.
  2. A 120 V-ac grounding-type receptacle outlet on the roof adjacent to the appliance on the supply side of the disconnect switch. [NFPA 54:9.4.2.3]
Where water stands on the roof at the appliance or in the passageways to the appliance, or where the roof is of a design having a water seal, a suitable platform, walkway, or both shall be provided above the waterline. Such platform(s) or walkway(s) shall be located adjacent to the appliance and control panels so that the appliance can be safely serviced where water stands on the roof. [NFPA 54:9.4.2.4]
Appliances located on roofs or other elevated locations shall be accessible. [NFPA 54:9.4.3.1]
Buildings exceeding 15 feet (4572 mm) in height shall have an inside means of access to the roof unless other means acceptable to the Authority Having Jurisdiction are used. [NFPA 54:9.4.3.2]
The inside means of access shall be a permanent or fold away inside stairway or ladder, terminating in an enclosure, scuttle, or trap door. Such scuttles or trap doors shall be at least 22 inches by 24 inches (559 mm by 610 mm) in size, shall open easily and safely under all conditions, especially snow; and shall be constructed so as to permit access from the roof side unless deliberately locked on the inside.

At least 6 feet (1829 mm) of clearance shall be available between the access opening and the edge of the roof or similar hazard, or rigidly fixed rails or guards a minimum of 42 inches (1067 mm) in height shall be provided on the exposed side. Where parapets or other building structures are utilized in lieu of guards or rails, they shall be a minimum of 42 inches (1067 mm) in height. [NFPA 54:9.4.3.3]

Permanent lighting shall be provided at the roof access. The switch for such lighting shall be located inside the building near the access means leading to the roof. [NFPA 54:9.4.3.4]
An attic or under-floor space in which an appliance is installed shall be accessible through an opening and passageway, not less than as large as the largest component of the appliance, and not less than 22 inches by 30 inches (559 mm by 762 mm).
Where the height of the passageway is less than 6 feet (1829 mm), the distance from the passageway access to the appliance shall not exceed 20 feet (6096 mm) measured along the centerline of the passageway. [NFPA 54:9.5.1.1]
The passageway shall be unobstructed and shall have solid flooring not less than 24 inches (610 mm) wide from the entrance opening to the appliance. [NFPA 54:9.5.1.2]
A level working platform not less than 30 inches by 30 inches (762 mm by 762 mm) shall be provided in front of the service side of the appliance. [NFPA 54:9.5.2]
A permanent 120 V receptacle outlet and a lighting fixture shall be installed near the appliance. The switch controlling the lighting fixture shall be located at the entrance to the passageway. [NFPA 54:9.5.3]
Type B and Type B-W gas vents shall comply with UL 441, and Type L gas vents shall comply with UL 641.
Listed vents shall be installed in accordance with Section 509.0 and the manufacturer's installation instructions. [NFPA 54:12.2.1]
Appliance vents shall not discharge into a space enclosed by screens having openings less than 1/4 of an inch (6.4 mm) mesh.
Except as permitted in Section 509.2.1 through Section 509.2.7, all appliances shall be connected to venting systems. [NFPA 54:12.3.1]
The following appliances shall not be required to be vented:
  1. A single listed booster-type (automatic instantaneous) water heater, when designed and used solely for the sanitizing rinse requirements of a dishwashing machine, provided that the appliance is installed with the draft hood in place and unaltered, if a draft hood is required, in a commercial kitchen having a mechanical exhaust system. Where installed in this manner, the draft hood outlet shall not be less than 36 inches (914 mm) vertically and 6 inches (152 mm) horizontally from any surface other than the appliance. [NFPA 54:12.3.2(5)]
  2. Other appliances listed for unvented use and not provided with flue collars. [NFPA 54:12.3.2(10)]
Where any or all of the appliances in Section 509.2.1(1) and Section 509.2.1(2) are installed so the aggregate input rating exceeds 20 (Btu/h)/ft3 (207 W/m3) of room or space in which it is installed, one or more shall be provided with venting systems or other approved means for conveying the vent gases to the outdoors so that the aggregate input rating of the remaining unvented appliance does not exceed 20 (Btu/h)/flt3 (207 W/m3). [NFPA 54:12.3.2.1]
Where the calculation includes the volume of an adjacent room or space, the room or space in which the appliances are installed shall be directly connected to the adjacent room or space by a doorway, archway, or other opening of comparable size that cannot be closed. [NFPA 54:12.3.2.2]
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications and to vent industrial appliances, particularly where the process itself requires fume disposal. [NFPA 54:12.3.3]
The operation of industrial appliances such that its flue gases are discharged directly into a large and well-ventilated space shall be permitted. [NFPA 54:12.3.4]
Listed direct-vent appliances shall be installed in accordance with the manufacturer's installation instructions and Section 509.8.2. [NFPA 54:12.3.5]
Appliances incorporating integral venting means shall be installed in accordance with the manufacturer's installation instructions, Section 509.8 and Section 509.8.1. [NFPA 54:12.3.6]
Venting systems shall be designed and constructed to convey flue, vent, or both gases to the outdoors. [NFPA 54:12.1]
A venting system shall satisfy the draft requirements of the appliance in accordance with the manufacturer's instructions. [NFPA 54:12.4.1]
Appliances required to be vented shall be connected to a venting system designed and installed in accordance with the provisions of Section 509.4 through Section 509.15. [NFPA 54:12.4.2]
Mechanical draft systems shall be listed and installed in accordance with both the appliance and the mechanical draft system manufacturer's installation instructions. [NFPA 54:12.4.3.1]
Appliances requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design. [NFPA 54:12.4.3.2]
Forced draft systems and 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. [NFPA 54:12.4.3.3]
Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. [NFPA 54:12.4.3.4]
Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners where the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. [NFPA 54:12.4.3.5]
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 509.8 and Section 509.8.1 of this code. [NFPA 54:12.4.3.6]
Ventilating hoods and exhaust systems shall be permitted to be used to vent appliances installed in commercial applications. [NFPA 54:12.4.4.1]
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 where the damper is open to a position to properly vent the appliance and where the power means of exhaust is in operation. [NFPA 54:12.4.4.2]
Venting systems shall not extend into or pass through a fabricated air duct or furnace plenum. [NFPA 54:12.4.5.1]
Where a venting system passes through an above-ceiling air space or other nonducted portion of an air-handling system, it shall conform to one of the following requirements:
  1. The venting system shall be a listed special gas vent, other 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 vent system shall be installed such that no fittings or joints between sections are installed in the above-ceiling space.
  3. The venting system shall be installed in a conduit or enclosure with joints between the interior of the enclosure and the ceiling space sealed. [NFPA 54:12.4.5.2]
The type of venting system to be used shall be in accordance with Table 509.4. [NFPA 54:12.5.1]

TABLE 509.4
TYPE OF VENTING SYSTEM TO BE USED [NFPA 54: TABLE 12.5.1]

APPLIANCES TYPE OF VENTING SYSTEM LOCATION OF REQUIREMENTS
Listed Category I appliances Type B gas vent Section 509.6
Listed appliances equipped with draft hood Chimney Section 509.5
Appliances listed for use with Type B gas vent Single-wall metal pipe
Listed chimney lining system for gas venting
Special gas vent listed for appliances
Section 509.7

Section 509.5.3


Section 509.4.3
Listed vented wall furnaces Type B-W gas vent Section 509.6(2), Section 509.6.1.2
Category II appliances
Category III appliances
Category IV appliances
As specified or furnished by manufacturers of listed appliances Section 509.4.1 and Section 509.4.3
Appliances that can be converted to use solid fuel

Unlisted combination gas- and oil-burning appliances

Combination gas- and solid-fuel-burning appliances

Appliance listed for use with chimneys only

Unlisted appliances
Chimney Section 509.5
Listed combination gas- and oil-burning appliances Type L vent

Chimney
Section 509.6

Section 509.5
Decorative appliances in vented fireplace Chimney UMC Section 911.2
Gas-fired toilets Single-wall metal pipe Section 509.7
Direct-vent appliances Section 509.2.6
Appliances with integral vents Section 509.2.7
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 instruction shall identify the specific plastic piping material. [NFPA 54:12.5.2]
Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer's installation instructions. Where primer is required, it shall be of a contrasting color. [NFPA 54:12.5.3]
Special gas vents shall be listed and installed in accordance with the special gas vent manufacturer's installation instructions. [NFPA 54:12.5.4]
Factory-built chimneys shall be installed in accordance with the manufacturer's installation instructions. Factory-built chimneys used to vent appliances that operate at positive vent pressure shall be listed for such application. [NFPA 54:12.6.1.1]
Decorative shrouds addressed in Section 509.5.4.3 shall comply with UL 103 for factory-built residential chimneys.
Factory-built chimneys shall comply with the requirements of UL 103 or UL 959. Factory-built chimneys for use with wood-burning appliances shall comply with the Type HT requirements of UL 103. [NFPA 211:6.1.3.1]
Metal chimneys shall be in accordance with NFPA 211. [NFPA 54:12.6.1.2]
Masonry chimneys shall be in accordance with NFPA 211 and lined with approved clay flue lining, a listed chimney lining system, or other approved material that resists corrosion, erosion, softening, or cracking from vent gases at temperatures not exceeding 1800°F (982°C).

Exception: Masonry chimney flues lined with a chimney lining system specifically listed for use with listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be permitted. 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 bum gas only. Do not connect to solid- or liquid-fuel-burning appliances or incinerators." [NFPA 54:12.6.1.3]

A chimney for a residential-type or low-heat appliance shall extend not less than 3 feet (914 mm) above the highest point where it passes through the roof of a building and not less than 2 feet (610 mm) higher than a portion of a building within a horizontal distance of 10 feet (3048 mm). (See Figure 509.5.4) [NFPA 54:12.6.2.1]

FIGURE 509.5.4
TYPICAL TERMINATION LOCATIONS FOR CHIMNEYS AND SINGLE-WALL METAL PIPES SERVING RESIDENTIAL-TYPE AND LOW-HEAT APPLIANCE [NFPA: 54: FIGURE A.12.6.2.1]

A chimney for medium-heat appliances shall extend at least 10 feet (3048 mm) higher than any portion of any building within 25 feet (7620 mm). [NFPA 54:12.6.2.2]
A chimney shall extend not less than 5 feet (1524 mm) above the highest connected appliance draft hood outlet or flue collar. [NFPA 54:12.6.2.3]
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. [NFPA 54:12.6.2.4]
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 in accordance with one of the following methods:
  1. Those listed in Section 510.0.
  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 or 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 or greater than seven times the smaller 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. [NFPA 54:12.6.3.1]
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 shall be cleaned where previously used for venting solid- or liquid-fuel-burning appliances or fireplaces. [NFPA 54:12.6.4.1]
Chimneys shall be lined in accordance with NFPA 211.

Exception: Existing chimneys shall be permitted to have their use continued when an appliance is replaced by an appliance of similar type, input rating, and efficiency, where the chimney complies with Section 509.5.6 through Section 509.5.6.3 and the sizing of the chimney is in accordance with Section 509.5.5. [NFPA 54:12.6.4.2]

Cleanouts shall be examined to determine that they will remain tightly closed where not in use. [NFPA 54:12.6.4.3]
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 in accordance with NFPA 211, and shall be approved for the appliances to be attached. [NFPA 54:12.6.4.4]
An appliance shall not be connected to a chimney flue serving a separate appliance designed to bum solid fuel. [NFPA 54:12.6.5.1]
Where one chimney 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 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 gas appliance is automatically controlled, it shall be equipped with a safety shutoff device. [NFPA 54:12.6.5.2]
A listed combination gas- and solid-fuel-burning appliance connected to a single chimney flue shall be 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. [NFPA 54:12.6.5.3]
A single chimney flue serving a listed combination gas- and oil-burning appliance shall be sized to properly vent the appliance. [NFPA 54:12.6.5.4]
All portions of chimneys shall be supported for the design and weight of the materials employed. Listed factory-built chimneys shall be supported and spaced in accordance with the manufacturer's installation instructions. [NFPA 54:12.6.6]
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 be installed, so its upper edge is not less than 6 inches (152 mm) below the lower edge of the lowest chimney inlet opening. [NFPA 54:12.6.7]
The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within a masonry chimney shall not be used to vent another appliance.

Exception The insertion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer's instructions. [NFPA 54:12.6.8.1]

The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within masonry, metal, or factory-built chimney flue shall not be used to supply combustion air.

Exception: Direct-vent appliances designed for installation in a solid-fuel-burning fireplace where installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.6.8.2]

The installation of gas vents shall meet the following requirements:
  1. Gas vents shall be installed in accordance with the manufacturer's installation instructions.
  2. 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.
  3. 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 bum gas. Do not connect to solid or liquid fuel-burning appliances or incinerators."
  4. Screws, rivets, and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from the appliance draft hood outlet, flue collar, or single-wall metal connector to a double-wall vent. [NFPA 54:12.7.1]
A gas vents shall terminate in accordance with one of the following:
  1. Gas vents that are 12 inches (300 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 509.6.1 and Table 509.6.1.
  2. Gas vents that are over 12 inches (300 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. Industrial appliances as provided in Section 509.2.5.
  4. Direct-vent systems as provided in Section 509.2.6.
  5. Appliances with integral vents as provided in Section 509.2.7.
  6. Mechanical draft systems as provided in Section 509.3.3 through Section 509.3.3.5.
  7. Ventilating hoods and exhaust systems as provided in Section 509.3.4 and Section 509.3.4.1. [NFPA 54:12.7.2(1)]

TABLE 509.6.1
ROOF SLOPE HEIGHTS
[NFPA 54: TABLE 12.7.2]

ROOF PITCH H (minimum) (feet)
Flat to 6/12 1.0
Over 6/12 to 7/12 1.25
Over 7/12 to 8/12 1.5
Over 8/12 to 9/12 2.0
Over 9/12 to 10/12 2.5
Over 10/12 to 11/12 3.25
Over 11/12 to 12/12 4.0
Over 12/12 to 14/12 5.0
Over 14/12 to 16/12 6.0
Over 16/12 to 18/12 7.0
Over 18/12 to 20/12 7.5
Over 20/12 to 21/12 8.0

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

FIGURE 509.6.1
TERMINATION LOCATIONS FOR GAS VENTS WITH LISTED CAPS 12 INCHES OR LESS IN SIZE AT LEAST 8 FEET FROM A VERTICAL WALL [NFPA 54: FIGURE 12.7.2]

A Type B or a Type L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. [NFPA 54:12.7.2(2)]
A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace. [NFPA 54:12.7.2(3)]
A gas vent extending through an exterior wall shall not terminate adjacent to the wall or below eaves or parapets, except as provided in Section 509.2.6 and Section 509.3.3 through Section 509.3.3.5. [NFPA 54:12.7.2(4)]
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 the manufacturer's installation instructions. [NFPA 54:12.7.2(5)]
All gas vents shall extend through the roof flashings roof jack, or roof thimble and terminate with a listed cap or listed roof assembly. [NFPA 54:12.7.2(6)]
A gas vent shall terminate at least 3 feet (914 mm) above a forced air inlet located within 10 feet (3048 mm). [NFPA 54:12.7.2(7)]
Where a vent passes through an insulated assembly, an approved metal shield shall be installed between the vent and insulation. The shield shall extend not less than 2 inches (51 mm) above the insulation and be secured to the structure in accordance with the manufacturer's installation instructions.
Venting systems shall be sized and constructed in accordance with Section 510.0 or other approved engineering methods and the gas vent and the appliance manufacturer's instructions. [NFPA 54:12.7.3]
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:
  1. The provisions of Section 510.0.
  2. Vents serving fan-assisted combustion system appliances, or combinations of fan-assisted combustion systems and draft-hood-equipped appliances, shall be sized in accordance with Section 510.0 or other approved engineering methods.
  3. 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 or exceeding seven times the draft hood outlet area.
  4. 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 or exceeding seven times the smaller draft hood outlet area.
  5. Approved engineering practices. [NFPA 54:12.7.3.1]
Type B and Type L vents sized in accordance with Section 509.6.2.1(3) or Section 509.6.2.1(4) 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 (1.05 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 not be greater than 75 percent of the vertical height of the vent. [NFPA 54:12.7.3.2]
The sizing of gas vents for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturer's instructions. The sizing of plastic pipe specified by the appliance manufacturer as a venting material for Category II, Category III, and Category IV appliances shall be in accordance with the appliance manufacturers' instructions. [NFPA 54:12.7.3.3]
Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods. [NFPA 54:12.7.3.4]
A common vent shall be permitted in multistory installations to vent Category I appliances located on more than one-floor level, provided 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 floor levels. [NFPA 54:12.7.4.1]

All appliances connected to the common vent shall be located in rooms separated from an occupiable space. Each of these rooms shall have provisions for an adequate supply of combustion, ventilation, and dilution air that is not supplied from an occupiable space. (See Figure 509.6.3.1) [NFPA 54:12.7.4.2]

FIGURE 509.6.3.1
PLAN VIEW OF PRACTICAL SEPARATION METHOD FOR MULTISTORY GAS VENTING [NFPA 54: FIGURE A.12.7.4.2]

The size of the connectors and common segments of multistory venting systems for appliances listed for use with a Type B double-wall gas vent shall be in accordance with Table 510.2(1), provided all of the following apply:
  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's gas input rate 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 vent segment, and of the interconnection tee at the base of that segment, is based on the total appliance's gas I input rate entering that segment and its available total height. [NFPA 54:12.7.4.3]
Gas vents shall be supported and spaced in accordance with the manufacturer's installation instructions. [NFPA 54:12.7.5]
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 label shall read: "This gas vent is for appliances that bum gas. Do not connect to solid- or liquid-fuel-burning appliances or incinerators." The Authority Having Jurisdiction shall determine whether its area constitutes such a locality. [NFPA 54:12.7.6]
Single-wall metal pipe shall be constructed of galvanized sheet steel not less than 0.0304 of an inch (0.7722 mm) thick or of other approved, noncombustible, corrosion-resistant material. [NFPA 54:12.8.1]
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). [NFPA 54:12.8.2]
The termination of single-wall metal pipe shall meet the following requirements:
  1. 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.
  2. Single-wall metal pipe shall extend at least 2 feet (610 mm) above the highest point where it passes through a roof of a building and at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm). (See Figure 509.5.4)
  3. An approved cap or roof assembly shall be attached to the terminus of a single-wall metal pipe. [NFPA 54:12.8.3]
Single-wall metal pipe shall not be used as a vent in dwellings and residential occupancies. [NFPA 54:12.8.4.1]
Single-wall metal pipe shall be used for runs directly from the space in which the appliance is located through the roof or exterior wall to the outer air. A pipe passing through a roof shall extend without interruption through the roof flashing, roof jacket, or roof thimble. [NFPA 54:12.8.4.2]
Single-wall metal pipe shall not originate in an unoccupied attic or concealed space and shall not pass through an attic, inside wall, concealed space, or floor. [NFPA 54:12.8.4.3]
Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have required clearances maintained.
Minimum clearances from single-wall metal pipe to combustible material shall be in accordance with Table 509.7.3.4(1). Reduced clearances from single-wall metal pipe to combustible material shall be as specified for vent connectors in Table 509.7.3.4(2). [NFPA 54:12.8.4.4]

TABLE 509.7.3.4(1)
CLEARANCE FOR CONNECTORS
[NFPA 54: TABLE 12.8.4.4]*

MINIMUM DISTANCE FROM COMBUSTIBLE MATERIAL (inches)
APPLIANCE 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 As listed
Residential boilers and furnaces with listed gas conversion burner and with draft hood 6 6 9 As listed
Residential appliances listed for use with Type L vents Not permitted As listed 9 As listed
Unlisted residential appliances with draft hood Not permitted 6 9 As listed
Residential and low-heat appliances other than those above Not permitted 9 18 As listed
Medium-heat appliances Not permitted Not permitted 36 As listed

For SI units: 1 inch = 25.4 mm

* These clearances shall apply unless the installation instructions of a listed appliance or connector specify different clearances, in which case the listed clearances shall apply.

Notes:

1 A — Equals the clearance with no protection specified in Table 509.7.3.4(1) and Table 509.7.3.4(2) and in the sections applying to various types of appliances.

2 B — Equals the reduced clearance permitted in accordance with Table 509.7.3.4(2).

3 The protection applied to the construction using combustible material shall extend far enough in each direction to make C equal to A.

FIGURE 509.7.3.4(1)1, 2, 3
EXTENT OF PROTECTION NECESSARY TO REDUCE CLEARANCES FROM GAS APPLIANCES OR VENT CONNECTORS
[NFPA 54: FIGURE 10.3.2.3(a)]

For SI units: 1 inch = 25.4 mm

Note: Masonry walls shall be attached to combustible walls using wall ties. Spacers shall not be used directly behind appliance or connector.

FIGURE 509.7.3.4(2)
WALL PROTECTION REDUCTION SYSTEM
[NFPA 54: FIGURE 10.3.2.3(b)]

For SI units: 1 inch = 25.4 mm

FIGURE 509.7.3.4(3)
MASONRY CLEARANCE REDUCTION SYSTEM
[NFPA 54: FIGURE 10.3.2.3(c)]

TABLE 509.7.3.4(2)
REDUCTION OF CLEARANCES WITH SPECIFIED FORMS OF PROTECTION1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
[NFPA 54: TABLE 10.2.3]

TYPE OF PROTECTION APPLIED TO AND COVERING ALL SURFACES OF COMBUSTIBLE MATERIAL WITHIN THE DISTANCE SPECIFIED AS THE REQUIRED CLEARANCE WITH NO PROTECTION [SEE FIGURE 509.7.3.4(1) THROUGH FIGURE 509.7.3.4(3)] WHERE THE REQUIRED CLEARANCE WITH NO PROTECTION FROM APPLIANCE, VENT CONNECTOR, OR SINGLE-WALL METAL PIPE IS:
36 (inches) 18 (inches) 12 (inches) 9 (inches) 6 (inches)
ALLOWABLE CLEARANCES WITH SPECIFIED PROTECTION (inches)
USE COLUMN 1 FOR CLEARANCES ABOVE APPLIANCE OR HORIZONTAL CONNECTOR. USE COLUMN 2 FOR CLEARANCES FROM APPLIANCES, VERTICAL CONNECTOR, AND SINGLE-WALL METAL PIPE.
ABOVE COLUMN 1 SIDES AND REAR COLUMN 2 ABOVE COLUMN 1 SIDES AND REAR COLUMN 2 ABOVE COLUMN 1 SIDES AND REAR COLUMN 2 ABOVE COLUMN 1 SIDES AND REAR COLUMN 2 ABOVE COLUMN 1 SIDES AND REAR COLUMN 2
(1) 31/2 inch thick masonry wall without ventilated air space 24 12 9 6 5
(2) 1/2 of an inch insulation board over 1 inch glass fiber or mineral wool batts 24 18 12 9 9 6 6 5 4 3
(3) 0.024 inch (nominal 24 gauge) sheet metal over 1 inch glass fiber or mineral wool batts reinforced with wire on rear face with ventilated air space 18 12 9 6 6 4 5 3 3 3
(4) 31/2 inch thick masonry wall with ventilated air space 12 6 6 6 6
(5) 0.024 inch (nominal 24 gauge) sheet metal with ventilated air space 18 12 9 6 6 4 5 3 3 2
(6) 1/2 of an inch thick insulation board with ventilated air space 18 12 9 6 6 4 5 3 3 3
(7) 0.024 inch (nominal 24 gauge) sheet metal with ventilated air space over 0.024 inch (nominal 24 gauge) sheet metal with ventilated air space 18 12 9 6 6 4 5 3 3 3
(8) 1 inch glass fiber or mineral wool batts sandwiched between two sheets 0.024 inch (nominal 24 gauge) sheet metal with ventilated air space 18 12 9 6 6 4 5 3 3 3

For SI units: 1 inch = 25.4 mm, °C = (°F—32)/1.8

Notes:

1 Reduction of clearances from combustible materials shall not interfere with combustion air, draft hood clearance and relief, and accessibility of servicing.

2 Clearances shall be measured from the outer surface of the combustible material to the nearest point on the surface of the appliance, disregarding an intervening protection applied to the combustible material.

3 Spacers and ties shall be of noncombustible material. No spacer or tie shall be used directly opposite the appliance or connector.

4 Where clearance reduction systems use a ventilated air space, adequate provision for air circulation shall be provided as described. [See Figure 509.7.3.4(2) and Figure 509.7.3.4(3)]

5 There shall be not less than 1 inch (25.4 mm) between clearance reduction systems and combustible walls and ceilings for reduction systems using a ventilated air space.

6 Where a wall protector is mounted on a single flat wall away from comers, it shall have a minimum 1 inch (25.4 mm) air gap. To provide air circulation, the bottom and top edges, or only the side and top edges, or edges shall be left open.

7 Mineral wool batts (blanket or board) shall have a minimum density of 8 pounds per cubic foot (lb/ft3) (128 kg/m3) and a minimum melting point of 1500°F (816°C).

8 Insulation material used as part of a clearance reduction system shall have a thermal conductivity of 1 British thermal unit inch per hour square foot degree Fahrenheit [Btu•in/(h•ft2•°F)] [0.1 W/(m•K)] or less.

9 There shall be not less than 1 inch (25.4 mm) between the appliance and the protector. In no case shall the clearance between the appliance and the combustible surface be reduced below that allowed in this table.

10 Clearances and thicknesses are minimum; larger clearances and thicknesses are acceptable.

11 Listed single-wall connectors shall be installed in accordance with the terms of their listing and the manufacturer's installation instructions.

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 a minimum of 4 inches (100 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 opening between the draft hood outlet and the thimble, the thimble shall be a minimum of 2 inches (50 mm) larger in diameter than the metal pipe.
  2. For unlisted appliances having draft hoods, the thimble shall be a minimum of 6 inches (150 mm) larger in diameter than the metal pipe.
  3. For residential and low-heat appliances, the thimble shall be a minimum of 12 inches (300 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. [NFPA 54:12.8.4.6]

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 at the top. The thimble shall be sized in accordance with Section 509.7.3.5. [NFPA 54:12.8.4.5]
Single-wall metal piping shall comply with the Section 509.7.4.1 through Section 509.7.4.3. [NFPA 54:12.8.5]
A venting system of a 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 510.0.
  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 exceed seven times the draft hood outlet area.
  3. Other approved engineering methods. [NFPA 54:12.8.5(1)]
Where a single-wall metal pipe is used and has a shape other than round, it shall have an effective area equal to the effective area of the round pipe for which it is substituted, and the internal dimension of the pipe shall be not less than 2 inches (50 mm). [NFPA 54:12.8.5(2)]
The vent cap or a roof assembly shall have a venting capacity not less than that of the pipe to which it is attached. [NFPA 54:12.8.5(3)]
Portions of single-wall metal pipe shall be supported for the design and weight of the material employed. [NFPA 54:12.8.6]
Single-wall metal pipe shall comply with the marking provisions of Section 509.6.5. [NFPA 54:12.8.7]
A mechanical draft venting system shall terminate at least 3 feet (914 mm) above any forced air inlet located within 10 feet (3048 mm) (See Figure 509.8).

FIGURE 509.8
EXIT TERMINALS OF MECHANICAL DRAFT AND DIRECT-VENT VENTING SYSTEMS
[NFPA 54: FIGURE A.12.9]

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. [NFPA 54:12.9.1]
A mechanical draft venting system of other than direct-vent type shall terminate not less than 4 feet (1219 mm) below, 4 feet (1219 mm) horizontally from, or 1 foot (305 mm) above a door, operable window, or gravity air inlet into a building. The bottom of the vent terminal shall be located not less than 12 inches (305 mm) above finished ground level. [NFPA 54:12.9.2]
The vent terminal of a direct-vent appliance with an input of 10 000 Btu/h (2.93 kW) or less shall be located at least 6 inches (152 mm) from any air opening into a building, an appliance with an input over 10 000 Btu/h (2.9.3 kW) but not over 50 000 Btu/h (14.7 kW) shall be installed with a 9 inch (229 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. [NFPA 54:12.9.3]
Through-the-wall vents for Category II and Category 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 Category III appliances, this provision shall also apply.

Drains for condensate shall be installed in accordance with the appliance and the vent manufacturer's installation instructions. [NFPA 54:12.9.4]

Where vents, including those for direct-vent appliances or combustion air intake pipes, 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. [NFPA 54:12.9.5]
Vent systems for Category IV appliances that terminate through an outside wall of a building and discharge flue gases perpendicular to the adjacent wall shall be located not less than 10 feet (3048 mm) horizontally from an operable opening in an adjacent building.

Exception: This shall not apply to vent terminals that are 2 feet (610 mm) or more above or 25 feet (7620 mm) or more below operable openings. [NFPA 54:12.9.6]

Provision shall be made to collect and dispose of condensate from venting systems serving Category II and Category IV appliances and noncategorized condensing appliances in accordance with Section 509.8.3. [NFPA 54:12.10.1]
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 Category III appliances in accordance with Section 509.8.3. [NFPA 54:12.10.2]
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. [NFPA 54:12.11.1]
A vent connector shall be made of noncombustible, corrosion-resistant material capable of withstanding the vent gas temperature produced by the appliance and of a thickness to withstand physical damage. [NFPA 54:12.11.2.1]
Where the vent connector used for an appliance having a draft hood or a Category I appliance is located in or passes through an unconditioned area, attic or crawl space, that portion of the vent connector shall be listed Type B, Type L, or listed vent material having equivalent insulation qualities.

Exception: Single-wall metal pipe located within the exterior walls of the building and located in an unconditioned area other than an attic or a crawl space having a local 99 percent winter design temperature of 5°F (-15°C) or higher. [NFPA 54:12.11.2.2]

Vent connectors for residential-type appliances shall comply with the following:
  1. Vent connectors for listed appliances having draft hoods, appliances having draft hoods and equipped with listed conversion burners, and Category I appliances that are not installed in attics, crawl spaces, or other unconditioned areas shall be one of the following:
    1. Type B or Type L vent material.
    2. Galvanized sheet steel not less than 0.018 of an inch (0.457 mm) thick.
    3. Aluminum (1100 or 3003 alloy or equivalent) sheet not less than 0.027 of an inch (0.686 mm) thick.
    4. Stainless steel sheet not less than 0.012 of an inch (0.305 mm) thick.
    5. Smooth interior wall metal pipe having resistance to heat and corrosion equal to or greater than that of Section 509.10.1.2(1)(b), Section 509.10.1.2(1)(c), or Section 509.10.1.2(l)(d).
    6. A listed vent connector.
  2. Vent connectors shall not be covered with insulation.

Exception: Listed insulated vent connectors shall be installed in accordance with the manufacturer's installation instructions. [NFPA 54:12.11.2.3]

A vent connector for a non-residential 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 509.10.1.3. Factory-built chimney sections shall be joined together in accordance with the chimney manufacturer's instructions. [NFPA 54:12.11.2.4]

TABLE 509.10.1.3
MINIMUM THICKNESS FOR GALVANIZED STEEL VENT CONNECTORS FOR LOW-HEAT APPLIANCES
[NFPA 54: TABLE 12.11.2.4]

DIAMETER OF CONNECTOR
(inches)
MINIMUM THICKNESS
(inches)
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 units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m2

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 509.10.1.4 and shall comply with the following:
  1. A steel vent connector for an appliance with a vent gas temperature in excess of 1000°F (538°C) measured at the entrance to the connector shall be lined with medium-duty fire brick 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 inches (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. [NFPA 54:12.11.2.5]

TABLE 509.10.1.4
MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES
[NFPA 54: TABLE 12.11.2.5]

VENT CONNECTOR SIZE
DIAMETER
(inches)
AREA
(square Inches)
MINIMUM THICKNESS
(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 Exceeding 254 0.123

For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m2

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 510.0 or other approved engineering methods. [NFPA 54:12.11.3.1]
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 alternative 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. [NFPA 54:12.11.3.2]
Where two or more appliances are connected to a common vent or chimney, each vent connector shall be sized in accordance with Section 510.0 or other approved engineering methods. [NFPA 54:12.11.3.3]

As an alternative method applicable where 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. [NFPA 54:12.11.3.4]

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 clearance to combustible material and sized in accordance with Section 510.0 or other approved engineering methods. [NFPA 54:12.11.3.5]

As an alternative 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. [NFPA 54:12.11.3.6]

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. [NFPA 54:12.11.3.7]
Where two or more openings are provided into one chimney flue or vent, either of the following shall apply:
  1. The openings shall be at different levels.
  2. 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. [NFPA 54:12.11.4.1]
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. [NFPA 54:12.11.4.2]
Vent connectors serving Category I appliances shall not be connected to a portion of a mechanical draft system operating under positive static pressure, such as those serving Category III or Category IV appliances. [NFPA 54:12.11.4.3]
Minimum clearances from vent connectors to combustible material shall comply with Table 509.7.3.4(1).

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 509.7.3.4(2). [NFPA 54:12.11.5]

Joints between sections of connector piping and connections to flue collars or draft hood outlets shall be fastened in accordance with 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 manufacturer's instructions.
  3. Other approved means. [NFPA 54:12.11.6]
A vent connector shall be installed without any dips or sags and shall slope upward toward the vent or chimney at least 1/4 inch per foot (20.8 mm/m).

Exception: Vent connectors attached to a mechanical draft system installed in accordance with appliance and draft system manufacturer's instructions. [NFPA 54:12.11.7]

The length of vent connectors shall comply with Section 509.10.7.1 or Section 509.10.7.2.
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. [NFPA 54:12.11.8.1]
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. The maximum length of an individual connector for a chimney or vent system serving multiple appliances, from the appliance outlet to the junction with the common vent or another connector, shall be 100 percent of the height of the chimney or vent. [NFPA 54:12.11.8.2]
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. [NFPA 54:12.11.9]
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 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. [NFPA 54:12.11.10]
The entire length of a vent connector shall be readily accessible for inspection, cleaning, and replacement. [NFPA 54:12.11.11]
A vent connector shall not be connected to a chimney flue serving a fireplace unless the fireplace flue opening is permanently sealed. [NFPA 54:12.11.12]
A vent connector shall not pass through a ceiling, floor, or fire-resistance-rated wall. A single-wall metal pipe connector shall not pass through an interior wall.

Exception: Vent connectors made of listed Type B or Type L vent material and serving listed appliances with draft hoods and other appliances listed for use with Type B gas vents that pass through walls or partitions constructed of combustible material shall be installed with not less than the listed clearance to combustible material.

Vent connectors for medium-heat appliances shall not pass through walls or partitions constructed of combustible material. [NFPA 54:12.11.13.2]
The vent connectors for Category II, Category III, and Category IV appliances shall be in accordance with Section 509.4 through Section 509.4.3. [NFPA 54:12.12]
Vented appliances shall be installed with draft hoods.

Exception: Dual oven-type combination ranges; incinerators; direct-vent appliances; fan-assisted combustion system appliances; appliances requiring chimney draft for operation; single firebox boilers equipped with conversion burners with inputs exceeding 400 000 Btu/h (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 listed vented appliances shall be installed without alteration, exactly as furnished and specified by the appliance manufacturer. [NFPA 54:12.13.2]

Where a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, be of a listed or approved type, and, in the absence of other instructions, 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. [NFPA 54:12.13.2.1]

Where a draft hood of special design is needed or preferable, the installation shall be approved and in accordance with the recommendations of the appliance manufacturer. [NFPA 54:12.13.2.2]

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 installation instructions. In the absence of manufacturer's installation instructions, the device shall be attached to the flue collar of the appliance or as near to the appliance as practical. [NFPA 54:12.13.3]
Appliances requiring controlled chimney draft shall be permitted to be equipped with listed double-acting barometric draft regulators installed and adjusted in accordance with the manufacturer's installation instructions. [NFPA 54:12.13.4]
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 a difference in pressure between the hood or regulator and the combustion air supply. [NFPA 54:12.13.5]
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 a 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. [NFPA 54:12.13.6]
A draft hood shall be located so that its relief opening is not less than 6 inches (152 mm) from a 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 not be less than that specified on the label. Such clearances shall not be reduced. [NFPA 54:12.13.7]
A manually operated damper shall not be placed in an appliance vent connector. Fixed baffles shall not be classified as manually operated dampers. [NFPA 54:12.14]
An automatically operated vent damper shall be of a listed type. [NFPA 54:12.15]
Automatically operated vent dampers for oil fired appliances shall comply with UL 17. The automatic damper control shall comply with UL 378.
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 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. Vent dampers serving listed appliances installed in accordance with Section 510.1 or Section 510.2 or other approved engineering methods.
  5. Approved economizers, heat reclaimers, and recuperators installed in venting systems of appliances not required to be equipped with draft hoods provided the appliance manufacturer's installation instructions cover the installation of such a device in the venting system and performance in accordance with Section 509.3 and Section 509.3.1 is obtained. [NFPA 54:12.16]
Table 510.1.2(1) through Table 510.1.2(6) shall not be used where obstructions 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 installation 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 though 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. [NFPA 54:13.1.1]
Where the vent size determined from the tables is smaller than the appliance draft hood outlet or flue collar, the use of the smaller size shall be permitted provided that the installation is in accordance with the following requirements:
  1. The total vent height (H) is not less than 10 feet (3048 mm).
  2. Vents for appliance draft hood outlets or flue collars 12 inches (300 mm) in diameter or smaller are not reduced more than one table size.
  3. Vents for appliance draft hood outlets or flue collars exceeding 12 inches (300 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 exceeds 4 inches (100 mm) in diameter. A 3 inch (80 mm) diameter vent shall not be connected to a 4 inch (100 mm) diameter draft hood outlet. This provision shall not apply to fan-assisted appliances. [NFPA 54:13.1.2]
Single-appliance venting configurations with zero lateral lengths in Table 510.1.2(1), Table 510.1.2(2), and Table 510.1.2(5) shall not have elbows in the venting system. Single-appliance venting with lateral lengths includes 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 offsets combined shall not exceed that specified in Table 510.1.2(1) through Table 510.1.2(5). [NFPA 54:13.1.3]

TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)]*

  NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
  VENT DIAMETERD (inch)
3 4 5 6 7
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
HEIGHT
H
(feet)
LATERAL
L
(feet)
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
6 0 0 78 46 0 152 86 0 251 141 0 375 205 0 524 285
  2 13 51 36 18 97 67 27 157 105 32 232 157 44 321 217
  4 21 49 34 30 94 64 39 153 103 50 227 153 66 316 211
  6 25 46 32 36 91 61 47 149 100 59 223 149 78 310 205
8 0 0 84 50 0 165 94 0 276 155 0 415 235 0 583 320
  2 12 57 40 16 109 75 25 178 120 28 263 180 42 365 247
  5 23 53 38 32 103 71 42 171 115 53 255 173 70 356 237
  8 28 49 35 39 98 66 51 164 109 64 247 165 84 347 227
10 0 0 88 53 0 175 100 0 295 166 0 447 255 0 631 345
  2 12 61 42 17 118 81 23 194 129 26 289 195 40 402 273
  5 23 57 40 32 113 77 41 187 124 52 280 188 68 392 263
  10 30 51 36 41 104 70 54 176 115 67 267 175 88 376 245
15 0 0 94 58 0 191 112 0 327 187 0 502 285 0 716 390
  2 11 69 48 15 136 93 20 226 150 22 339 225 38 475 316
  5 22 65 45 30 130 87 39 219 142 49 330 217 64 463 300
  10 29 59 41 40 121 82 51 206 135 64 315 208 84 445 288
  15 35 53 37 48 112 76 61 195 128 76 301 198 98 429 275
20 0 0 97 61 0 202 119 0 349 202 0 540 307 0 776 430
  2 10 75 51 14 149 100 18 250 166 20 377 249 33 531 346
  5 21 71 48 29 143 96 38 242 160 47 367 241 62 519 337
  10 28 64 44 38 133 89 50 229 150 62 351 228 81 499 321
  15 34 58 40 46 124 84 59 217 142 73 337 217 94 481 308
  20 48 52 35 55 116 78 69 206 134 84 322 206 107 464 295
30 0 0 100 64 0 213 128 0 374 220 0 587 336 0 853 475
  2 9 81 56 13 166 112 14 283 185 18 432 280 27 613 394
  5 21 77 54 28 160 108 36 275 176 45 421 273 58 600 385
  10 27 70 50 37 150 102 48 262 171 59 405 261 77 580 371
  15 33 64 NA 44 141 96 57 249 163 70 389 249 90 560 357
  20 56 58 NA 53 132 90 66 237 154 80 374 237 102 542 343
  30 NA NA NA 73 113 NA 88 214 NA 104 346 219 131 507 321
50 0 0 101 67 0 216 134 0 397 232 0 633 363 0 932 518
  2 8 86 61 11 183 122 14 320 206 15 497 314 22 715 445
  5 20 82 NA 27 177 119 35 312 200 43 487 308 55 702 438
  10 26 76 NA 35 168 114 45 299 190 56 471 298 73 681 426
  15 59 70 NA 42 158 NA 54 287 180 66 455 288 85 662 413
  20 NA NA NA 50 149 NA 63 275 169 76 440 278 97 642 401
  30 NA NA NA 69 131 NA 84 250 NA 99 410 259 123 605 376
100 0 NA NA NA 0 218 NA 0 407 NA 0 665 400 0 997 560
  2 NA NA NA 10 194 NA 12 354 NA 13 566 375 18 831 510
  5 NA NA NA 26 189 NA 33 347 NA 40 557 369 52 820 504
  10 NA NA NA 33 182 NA 43 335 NA 53 542 361 68 801 493
  15 NA NA NA 40 174 NA 50 321 NA 62 528 353 80 782 482
  20 NA NA NA 47 166 NA 59 311 NA 71 513 344 90 763 471
  30 NA NA NA NA NA NA 78 290 NA 92 483 NA 115 726 449
  50 NA NA NA NA NA NA NA NA NA 147 428 NA 180 651 405

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.

TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)] (continued)

  NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
  VENT DIAMETERD (inch)
8 9 10 12 14
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
HEIGHT
H
(feet)
LATERAL
L
(feet)
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
6 0 0 698 370 0 897 470 0 1121 570 0 1645 850 0 2267 1170
  2 53 425 285 63 543 370 75 675 455 103 982 650 138 1346 890
  4 79 419 279 93 536 362 110 668 445 147 975 640 191 1338 880
  6 93 413 273 110 530 354 128 661 435 171 967 630 219 1330 870
8 0 0 780 415 0 1006 537 0 1261 660 0 1858 970 0 2571 1320
  2 50 483 322 60 619 418 71 770 515 98 1124 745 130 1543 1020
  5 83 473 313 99 607 407 115 758 503 154 1110 733 199 1528 1010
  8 99 463 303 117 596 396 137 746 490 180 1097 720 231 1514 1000
10 0 0 847 450 0 1096 585 0 1377 720 0 2036 1060 0 2825 1450
  2 48 533 355 57 684 457 68 852 560 93 1244 850 124 1713 1130
  5 81 522 346 95 671 446 112 839 547 149 1229 829 192 1696 1105
  10 104 504 330 122 651 427 142 817 525 187 1204 795 238 1669 1080
15 0 0 970 525 0 1263 682 0 1596 840 0 2380 1240 0 3323 1720
  2 45 633 414 53 815 544 63 1019 675 86 1495 985 114 2062 1350
  5 76 620 403 90 800 529 105 1003 660 140 1476 967 182 2041 1327
  10 99 600 386 116 777 507 135 977 635 177 1446 936 227 2009 1289
  15 115 580 373 134 755 491 155 953 610 202 1418 905 257 1976 1250
20 0 0 1057 575 0 1384 752 0 1756 930 0 2637 1350 0 3701 1900
  2 41 711 470 50 917 612 59 1150 755 81 1694 1100 107 2343 1520
  5 73 697 460 86 902 599 101 1133 738 135 1674 1079 174 2320 1498
  10 95 675 443 112 877 576 130 1105 710 172 1641 1045 220 2282 1460
  15 111 654 427 129 853 557 150 1078 688 195 1609 1018 248 2245 1425
  20 125 634 410 145 830 537 167 1052 665 217 1578 990 273 2210 1390
30 0 0 1173 650 0 1548 855 0 1977 1060 0 3004 1550 0 4252 2170
  2 33 826 535 42 1072 700 54 1351 865 74 2004 1310 98 2786 1800
  5 69 811 524 82 1055 688 96 1332 851 127 1981 1289 164 2759 1775
  10 91 788 507 107 1028 668 125 1301 829 164 1944 1254 209 2716 1733
  15 105 765 490 124 1002 648 143 1272 807 187 1908 1220 237 2674 1692
  20 119 743 473 139 977 628 160 1243 784 207 1873 1185 260 2633 1650
  30 149 702 444 171 929 594 195 1189 745 246 1807 1130 305 2555 1585
50 0 0 1297 708 0 1730 952 0 2231 1195 0 3441 1825 0 4934 2550
  2 26 975 615 33 1276 813 41 1620 1010 66 2431 1513 86 3409 2125
  5 65 960 605 77 1259 798 90 1600 996 118 2406 1495 151 3380 2102
  10 86 935 589 101 1230 773 118 1567 972 154 2366 1466 196 3332 2064
  15 100 911 572 117 1203 747 136 1536 948 177 2327 1437 222 3285 2026
  20 113 888 556 131 1176 722 151 1505 924 195 2288 1408 244 3239 1987
  30 141 844 522 161 1125 670 183 1446 876 232 2214 1349 287 3150 1910
100 0 0 1411 770 0 1908 1040 0 2491 1310 0 3925 2050 0 5729 2950
  2 21 1155 700 25 1536 935 30 1975 1170 44 3027 1820 72 4313 2550
  5 60 1141 692 71 1519 926 82 1955 1159 107 3002 1803 136 4282 2531
  10 80 1118 679 94 1492 910 108 1923 1142 142 2961 1775 180 4231 2500
  15 93 1095 666 109 1465 895 126 1892 1124 163 2920 1747 206 4182 2469
  20 105 1073 653 122 1438 880 141 1861 1107 181 2880 1719 226 4133 2438
  30 131 1029 627 149 1387 849 170 1802 1071 215 2803 1663 265 4037 2375
  50 197 944 575 217 1288 787 241 1688 1000 292 2657 1550 350 3856 2250

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

TABLE 510.1.2(1)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(a)] (continued)

  NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: CONNECTED DIRECTLY TO VENT
  VENT DIAMETERD (inch)
16 18 20 22 24
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
HEIGHT
H
(feet)
LATERAL
L
(feet)
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
6 0 0 2983 1530 0 3802 1960 0 4721 2430 0 5737 2950 0 6853 3520
  2 178 1769 1170 225 2250 1480 296 2782 1850 360 3377 2220 426 4030 2670
  4 242 1761 1160 300 2242 1475 390 2774 1835 469 3370 2215 555 4023 2660
  6 276 1753 1150 341 2235 1470 437 2767 1820 523 3363 2210 618 4017 2650
8 0 0 3399 1740 0 4333 2220 0 5387 2750 0 6555 3360 0 7838 4010
  2 168 2030 1340 212 2584 1700 278 3196 2110 336 3882 2560 401 4634 3050
  5 251 2013 1330 311 2563 1685 398 3180 2090 476 3863 2545 562 4612 3040
  8 289 2000 1320 354 2552 1670 450 3163 2070 537 3850 2530 630 4602 3030
10 0 0 3742 1925 0 4782 2450 0 5955 3050 0 7254 3710 0 8682 4450
  2 161 2256 1480 202 2868 1890 264 3556 2340 319 4322 2840 378 5153 3390
  5 243 2238 1461 300 2849 1871 382 3536 2318 458 4301 2818 540 5132 3371
  10 298 2209 1430 364 2818 1840 459 3504 2280 546 4268 2780 641 5099 3340
15 0 0 4423 2270 0 5678 2900 0 7099 3620 0 8665 4410 0 10 393 5300
  2 147 2719 1770 186 3467 2260 239 4304 2800 290 5232 3410 346 6251 4080
  5 229 2696 1748 283 3442 2235 355 4278 2777 426 5204 3385 501 6222 4057
  10 283 2659 1712 346 3402 2193 432 4234 2739 510 5159 3343 599 6175 4019
  15 318 2623 1675 385 3363 2150 479 4192 2700 564 5115 3300 665 6129 3980
20 0 0 4948 2520 0 6376 3250 0 7988 4060 0 9785 4980 0 11 753 6000
  2 139 3097 2000 175 3955 2570 220 4916 3200 269 5983 3910 321 7154 4700
  5 219 3071 1978 270 3926 2544 337 4885 3174 403 5950 3880 475 7119 4662
  10 273 3029 1940 334 3880 2500 413 4835 3130 489 5896 3830 573 7063 4600
  15 306 2988 1910 372 3835 2465 459 4786 3090 541 5844 3795 631 7007 4575
  20 335 2948 1880 404 3791 2430 495 4737 3050 585 5792 3760 689 6953 4550
30 0 0 5725 2920 0 7420 3770 0 9341 4750 0 11 483 5850 0 13 848 7060
  2 127 3696 2380 159 4734 3050 199 5900 3810 241 7194 4650 285 8617 5600
  5 206 3666 2350 252 4701 3020 312 5863 3783 373 7155 4622 439 8574 5552
  10 259 3617 2300 316 4647 2970 386 5803 3739 456 7090 4574 535 8505 5471
  15 292 3570 2250 354 4594 2920 431 5744 3695 507 7026 4527 590 8437 5391
  20 319 3523 2200 384 4542 2870 467 5686 3650 548 6964 4480 639 8370 5310
  30 369 3433 2130 440 4442 2785 540 5574 3565 635 6842 4375 739 8239 5225
50 0 0 6711 3440 0 8774 4460 0 11 129 5635 0 13 767 6940 0 16 694 8430
  2 113 4554 2840 141 5864 3670 171 7339 4630 209 8980 5695 251 10 788 6860
  5 191 4520 2813 234 5826 3639 283 7295 4597 336 8933 5654 394 10 737 6818
  10 243 4464 2767 295 5763 3585 355 7224 4542 419 8855 5585 491 10 652 6749
  15 274 4409 2721 330 5701 3534 396 7155 4511 465 8779 5546 542 10 570 6710
  20 300 4356 2675 361 5641 3481 433 7086 4479 506 8704 5506 586 10 488 6670
  30 347 4253 2631 412 5523 3431 494 6953 4421 577 8557 5444 672 10 328 6603
100 0 0 7914 4050 0 10 485 5300 0 13 454 6700 0 16 817 8600 0 20 578 10 300
  2 95 5834 3500 120 7591 4600 138 9577 5800 169 11 803 7200 204 14 264 8800
  5 172 5797 3475 208 7548 4566 245 9528 5769 293 11 748 7162 341 14 204 8756
  10 223 5737 3434 268 7478 4509 318 9447 5717 374 11 658 7100 436 14 105 8683
  15 252 5678 3392 304 7409 4451 358 9367 5665 418 11 569 7037 487 14 007 8610
  20 277 5619 3351 330 7341 4394 387 9289 5613 452 11 482 6975 523 13 910 8537
  30 319 5505 3267 378 7209 4279 446 9136 5509 514 11 310 6850 592 13 720 8391
  50 415 5289 3100 486 6956 4050 572 8841 5300 659 10 979 6600 752 13 354 8100

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

TABLE 510.1.2(2)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(b)]*

  NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
  VENT DIAMETERD (inch)
3 4 5 6 7
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
HEIGHT
H
(feet)
LATERAL
L
(feet)
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
6 0 38 77 45 59 151 85 85 249 140 126 373 204 165 522 284
  2 39 51 36 60 96 66 85 156 104 123 231 156 159 320 213
  4 NA NA 33 74 92 63 102 152 102 146 225 152 187 313 208
  6 NA NA 31 83 89 60 114 147 99 163 220 148 207 307 203
8 0 37 83 50 58 164 93 83 273 154 123 412 234 161 580 319
  2 39 56 39 59 108 75 83 176 119 121 261 179 155 363 246
  5 NA NA 37 77 102 69 107 168 114 151 252 171 193 352 235
  8 NA NA 33 90 95 64 122 161 107 175 243 163 223 342 225
10 0 37 87 53 57 174 99 82 293 165 120 444 254 158 628 344
  2 39 61 41 59 117 80 82 193 128 119 287 194 153 400 272
  5 52 56 39 76 111 76 105 185 122 148 277 186 190 388 261
  10 NA NA 34 97 100 68 132 171 112 188 261 171 237 369 241
15 0 36 93 57 56 190 111 80 325 186 116 499 283 153 713 388
  2 38 69 47 57 136 93 80 225 149 115 337 224 148 473 314
  5 51 63 44 75 128 86 102 216 140 144 326 217 182 459 298
  10 NA NA 39 95 116 79 128 201 131 182 308 203 228 438 284
  15 NA NA NA NA NA 72 158 186 124 220 290 192 272 418 269
20 0 35 96 60 54 200 118 78 346 201 114 537 306 149 772 428
  2 37 74 50 56 148 99 78 248 165 113 375 248 144 528 344
  5 50 68 47 73 140 94 100 239 158 141 363 239 178 514 334
  10 NA NA 41 93 129 86 125 223 146 177 344 224 222 491 316
  15 NA NA NA NA NA 80 155 208 136 216 325 210 264 469 301
  20 NA NA NA NA NA NA 186 192 126 254 306 196 309 448 285
30 0 34 99 63 53 211 127 76 372 219 110 584 334 144 849 472
  2 37 80 56 55 164 111 76 281 183 109 429 279 139 610 392
  5 49 74 52 72 157 106 98 271 173 136 417 271 171 595 382
  10 NA NA NA 91 144 98 122 255 168 171 397 257 213 570 367
  15 NA NA NA 115 131 NA 151 239 157 208 377 242 255 547 349
  20 NA NA NA NA NA NA 181 223 NA 246 357 228 298 524 333
  30 NA NA NA NA NA NA NA NA NA NA NA NA 389 477 305
50 0 33 99 66 51 213 133 73 394 230 105 629 361 138 928 515
  2 36 84 61 53 181 121 73 318 205 104 495 312 133 712 443
  5 48 80 NA 70 174 117 94 308 198 131 482 305 164 696 435
  10 NA NA NA 89 160 NA 118 292 186 162 461 292 203 671 420
  15 NA NA NA 112 148 NA 145 275 174 199 441 280 244 646 405
  20 NA NA NA NA NA NA 176 257 NA 236 420 267 285 622 389
  30 NA NA NA NA NA NA NA NA NA 315 376 NA 373 573 NA
100 0 NA NA NA 49 214 NA 69 403 NA 100 659 395 131 991 555
  2 NA NA NA 51 192 NA 70 351 NA 98 563 373 125 828 508
  5 NA NA NA 67 186 NA 90 342 NA 125 551 366 156 813 501
  10 NA NA NA 85 175 NA 113 324 NA 153 532 354 191 789 486
  15 NA NA NA 132 162 NA 138 310 NA 188 511 343 230 764 473
  20 NA NA NA NA NA NA 168 295 NA 224 487 NA 270 739 458
  30 NA NA NA NA NA NA 231 264 NA 301 448 NA 355 685 NA
  50 NA NA NA NA NA NA NA NA NA NA NA NA 540 584 NA

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1000 British thermal units per hour = 0.293 kW, 1 square inch = 0.000645 m2

* NA: Not applicable.

TABLE 510.1.2(2)
TYPE B DOUBLE-WALL GAS VENT [NFPA 54: TABLE 13.1(b)] (continued)*

  NUMBER OF APPLIANCES: SINGLE
APPLIANCE TYPE: CATEGORY I
APPLIANCE VENT CONNECTION: SINGLE-WALL METAL CONNECTOR
  VENT DIAMETERD (inch)
8 9 10 12
APPLIANCE INPUT RATING IN THOUSANDS OF BTU PER HOUR
HEIGHT
H
(feet)
LATERAL
L
(feet)
FAN NAT FAN NAT FAN NAT FAN NAT
Min Max Max Min Max Max Min Max Max Min Max Max
6 0 211 695 369 267 894 469 371 1118 569 537 1639 849
  2 201 423 284 251 541 368 347 673 453 498 979 648
  4 237 416 277 295 533 360 409 664 443 584 971 638
  6 263 409 271 327 526 352 449 656 433 638 962 627
8 0 206 777 414 258 1002 536 360 1257 658 521 1852 967
  2 197 482 321 246 617 417 339 768 513 486 1120 743
  5 245 470 311 305 604 404 418 754 500 598