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 701.4 through Section 701.9.3. Where the requirements of Section 701.4 are not met, outdoor air shall be introduced in accordance with methods covered in Section 701.6 through Section 701.9.3.
- This provision shall not apply to direct-vent appliances.
- Type 1 clothes dryers that arc provided with makeup air in accordance with Section 504.4.1. [NFPA 54:22.214.171.124]
Appliances of other than natural draft design and Category I vented appliances shall be provided with combustion, ventilation, and dilution air in accordance with the appliance manufacturer's instructions. [NFPA 54:126.96.36.199]
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 54:188.8.131.52]
Where exhaust fans, clothes dryers, and kitchen ventilation systems interfere with the operation of appliances, makeup air shall be provided. [NFPA 54:184.108.40.206]
The required volume of indoor air shall be determined in accordance with the method in Section 701.4.1 or Section 701.4.2, except that where the air infiltration rate is known to be less than 0.40 ACH (air change per hour), the method in Section 701.4.2 shall be used. The total required volume shall be the sum of the required volume calculated for 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 701.5, 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 54:220.127.116.11]
Where the air infiltration rate of a structure is known, the required volume shall be not less than the following [NFPA 54:18.104.22.168]:
For SI units: 1 cubic fool = 0.0283 m3, 1000 British thermal units per
hour = 0.293 kW
- For appliances other than fan-assisted, calculate using Equation 701.4.2(1). [NFPA 54:22.214.171.124(1)]
- For fan-assisted appliances, calculate using Equation 701.4.2(2). [NFPA 54: 126.96.36.199(2)]
- For purposes of these calculations, an infiltration rate greater than 0.60 ACH shall not be used in the equations. [NFPA 54:188.8.131.52(3)]
Required Volume other ≥ (21 ft3 /ACH) x (I other/1000 Btu/h) [Equation 701.4.2(1)]
Required Volume fan ≥ (15 ft3 /ACH) x (I fan/1000 Btu/h) [Equation 701.4.2(2)]
|I other||=||Appliances other than fan-assisted input in
Btu per hour
|I fan||=||Fan-assisted appliance input in Btu per
|ACH||=||Air change per hour (percent of volume
of space exchanged per hour, expressed
as a decimal)
Openings used to connect indoor spaces shall be sized and located in accordance with the following:
- 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 701.5). The dimension of air openings shall be not less than 3 inches (76 mm).
- 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 54:184.108.40.206]
Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with the methods in Section 701.6.1 or Section 701.6.2. 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:
- Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a free area of not less than 1 square inch per 4000 Btu/h (0.0005 m2/kW) of total input rating of appliances in the enclosure. [See Figure 701.6.1(1) and Figure 701.6.1(2)]
- Where communicating with the outdoors through horizontal ducts, each opening shall have a free area of not less than 1 square inch per 2000 Btu/h (0.001 m2/kW) of total input rating of appliances in the enclosure. [See Figure 701.6.1(3)] [NFPA 54:220.127.116.11]
For SI units: 1 foot = 304.8 mm
One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The appliance shall have clearances of not less than 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 701.6.2) and shall have a free area not less than the following:
- One square inch per 3000 Btu/h (0.0007 m2/kW) of the total input rating of appliances located in the enclosure.
- Not less than the sum of the areas of vent connectors in the space. [NFPA 54:18.104.22.168]
The use of a combination of indoor and outdoor combustion air shall be in accordance with Section 701.7.1 through Section 701.7.3. (See Appendix F for example calculations) [NFPA 54:9.3.4]
Where used, openings connecting the interior spaces shall be in accordance with Section 701.5. [NFPA 54:9.3.4(1)]
Outdoor openings shall be located in accordance with Section 701.6. [NFPA 54:9.3.4(2)]
The outdoor openings size shall be calculated in accordance with the following:
- The ratio of interior spaces shall be the volume of the communicating spaces divided by the required volume.
- The outdoor size reduction factor shall be one minus the ratio of interior spaces.
- The size of outdoor opening(s) shall be not less than the full size of outdoor opening(s) calculated in accordance with Section 701.6, 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 a supply of combustion, ventilation, and dilution air that is 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 rate of not less than 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 54:22.214.171.124]
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 54:126.96.36.199]
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 54:188.8.131.52]
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 54:184.108.40.206]
Screens shall be not less than 1/4 of an inch (6.4 mm) mesh. [NFPA 54:220.127.116.11]
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 where the louver fail to open during burner start-up and to shut down the main burner where the louvers close during burner operation. [NFPA 54:18.104.22.168]
Combustion air ducts shall comply with the following [NFPA 54:9.3.8]:
- Ducts shall be constructed of galvanized steel or a material
having equivalent corrosion resistance, strength, and
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one fireblock is removed. [NFPA 54:22.214.171.124]
- Ducts shall terminate in an unobstructed space, allowing free movement of combustion air to the appliances. [NFPA 54:126.96.36.199]
- Ducts shall serve a single space. [NFPA 54:188.8.131.52]
- Ducts shall not service 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 54:184.108.40.206]
- Ducts shall not be screened where terminating in an attic space. [NFPA 54:220.127.116.11]
- Combustion air intake openings located on the exterior of the building shall have the lowest side of the combustion air intake openings located not less than 12 inches (305 mm) vertically from the adjoining finished ground level. [NFPA 54:18.104.22.168]
- Horizontal upper combustion air ducts shall not be sloped downward toward the source of combustion air. [NFPA 54:22.214.171.124]
- 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 54:126.96.36.199]
Combustion air ducts or plenums shall not be installed so as to require openings in or penetrations through construction where fire dampers are required. Manually operated dampers shall not be installed in combustion-air openings. With prior approval, power-actuated movable louvers admitting combustion air shall be permitted to be used and, where installed, shall be electrically interlocked with the main burner fuel-supply valve so as to prevent fuel delivery unless the louvers are in the fully open position.
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]
No device or attachment shall be installed on an appliance that is capable of impairing the combustion of gas. [NFPA 54:9.1.15]
Bleed lines shall comply with the following requirements:
- Diaphragm-type valves shall be equipped to convey bleed gas to the outdoors or into the combustion chamber adjacent to a continuous pilot.
- 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.
- Bleed lines shall not terminate in the appliance flue or exhaust system.
- In the case of bleed lines entering the combustion chamber, the bleed line shall be located so the bleed gas will be readily ignited by the pilot and the heat liberated thereby will 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.
- Bleed lines from a diaphragm-type valve and vent lines 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]