UpCodes logo
// CODE SNIPPET

Section G2407 (304) Combustion, Ventilation and Dilution Air

Go To Full Code Chapter
G2407.1 (304.1) General
Air for combustion, ventilation and dilution of flue gases for appliances installed in buildings shall be provided by application of one of the methods prescribed in Sections G2407.5 through G2407.9. Where the requirements of Section G2407.5 are not met, outdoor air shall be introduced in accordance with one of the methods prescribed in Sections G2407.6 through G2407.9. Direct-vent appliances, gas appliances of other than natural draft design, vented gas appliances not designated as Category I and appliances equipped with power burners, shall be provided with combustion, ventilation and dilution air in accordance with the appliance manufacturer's instructions.
Exception: Type 1 clothes dryers that are provided with makeup air in accordance with Section G2439.5.
G2407.2 (304.2) Appliance Location
Appliances shall be located so as not to interfere with proper circulation of combustion, ventilation and dilution air.
G2407.3 (304.3) Draft Hood/Regulator Location
Where used, a draft hood or a barometric draft regulator shall be installed in the same room or enclosure as the appliance served to prevent any difference in pressure between the hood or regulator and the combustion air supply.
G2407.4 (304.4) Makeup Air Provisions
Where exhaust fans, clothes dryers and kitchen ventilation systems interfere with the operation of appliances, makeup air shall be provided.
G2407.5 (304.5) Indoor Combustion Air
The required volume of indoor air shall be determined in accordance with Section G2407.5.1 or G2407.5.2, except that where the air infiltration rate is known to be less than 0.40 air changes per hour (ACH), Section G2407.5.2 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 G2407.5.3, are considered to be part of the required volume.
G2407.5.1 (304.5.1) Standard Method
The minimum required volume shall be 50 cubic feet per 1,000 Btu/h (4.8 m3/kW) of the appliance input rating.
G2407.5.2 (304.5.2) Known Air-Infiltration-Rate Method
Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows:
For appliances other than fan-assisted, calculate volume using Equation 24-1.

(Equation 24-1)

For fan-assisted appliances, calculate volume using Equation 24-2.

(Equation 24-2)


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 purposes of this calculation, an infiltration rate greater than 0.60 ACH shall not be used in Equations 24-1 and 24-2.
G2407.5.3 (304.5.3) Indoor Opening Size and Location
Openings used to connect indoor spaces shall be sized and located in accordance with Sections G2407.5.3.1 and G2407.5.3.2 (see Figure G2407.5.3).

FIGURE G2407.5.3 (304.5.3)
ALL AIR FROM INSIDE THE BUILDING (see Section G2407.5.3)
G2407.5.3.1 (304.5.3.1) Combining Spaces on the Same Story
Where combining spaces on the same story, each opening shall have a minimum free area of 1 square inch per 1,000 Btu/h (2,200 mm2/kW) of the total input rating of all appliances in the space, but not less than 100 square inches (0.06 m2). One permanent opening shall commence within 12 inches (305 mm) of the top and one permanent opening shall commence within 12 inches (305 mm) of the bottom of the enclosure. The minimum dimension of air openings shall be not less than 3 inches (76 mm).
G2407.5.3.2 (304.5.3.2) Combining Spaces in Different Stories
The volumes of spaces in different stories shall be considered to be communicating spaces where such spaces are connected by one or more permanent openings in doors or floors having a total minimum free area of 2 square inches per 1,000 Btu/h (4402 mm2/kW) of total input rating of all appliances.
G2407.6 (304.6) Outdoor Combustion Air
Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with Section G2407.6.1 or G2407.6.2. The minimum dimension of air openings shall be not less than 3 inches (76 mm).
G2407.6.1 (304.6.1) Two-Permanent-Openings Method
Two permanent openings, one commencing within 12 inches (305 mm) of the top 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.
Where directly communicating with the outdoors, or where communicating with the outdoors through vertical ducts, each opening shall have a minimum free area of 1 square inch per 4,000 Btu/h (550 mm2/kW) of total input rating of all appliances in the enclosure [see Figures G2407.6.1(1) and G2407.6.1(2)].
Where communicating with the outdoors through horizontal ducts, each opening shall have a minimum free area of not less than 1 square inch per 2,000 Btu/h (1100 mm2/kW) of total input rating of all appliances in the enclosure [see Figure G2407.6.1(3)].


FIGURE G2407.6.1(1) [304.6.1(1)]
ALL AIR FROM OUTDOORS—INLET AIR FROM VENTILATED CRAWL SPACE AND OUTLET AIR TO VENTILATED ATTIC
(see Section G2407.6.1)

For SI: 1 foot = 304.8 mm.

FIGURE G2407.6.1(2) [304.6.1(2)]
ALL AIR FROM OUTDOORS THROUGH VENTILATED ATTIC
(see Section G2407.6.1)


FIGURE G2407.6.1(3) [304.6.1(3)]
ALL AIR FROM OUTDOORS
(see Section G2407.6.1)
G2407.6.2 (304.6.2) One-Permanent-Opening Method
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 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 through a vertical or horizontal duct to the outdoors, or spaces that freely communicate with the outdoors (see Figure G2407.6.2) and shall have a minimum free area of 1 square inch per 3,000 Btu/h (734 mm2/kW) of the total input rating of all appliances located in the enclosure and not less than the sum of the areas of all vent connectors in the space.

FIGURE G2407.6.2 (304.6.2)
SINGLE COMBUSTION AIR OPENING, ALL AIR FROM OUTDOORS
(see Section G2407.6.2)
G2407.7 (304.7) Combination Indoor and Outdoor Combustion Air
The use of a combination of indoor and outdoor combustion air shall be in accordance with Sections G2407.7.1 through G2407.7.3.
G2407.7.1 (304.7.1) Indoor Openings
Where used, openings connecting the interior spaces shall comply with Section G2407.5.3.
G2407.7.2 (304.7.2) Outdoor Opening Location
Outdoor opening(s) shall be located in accordance with Section G2407.6.
G2407.7.3 (304.7.3) Outdoor Opening(s) Size
The outdoor opening(s) size shall be calculated in accordance with the following:
  1. The ratio of interior spaces shall be the available volume of all communicating spaces divided by the required volume.
  2. The outdoor size reduction factor shall be one minus the ratio of interior spaces.
  3. The minimum size of outdoor opening(s) shall be the full size of outdoor opening(s) calculated in accordance with Section G2407.6, multiplied by the reduction factor. The minimum dimension of air openings shall be not less than 3 inches (76 mm).
G2407.8 (304.8) Engineered Installations
Engineered combustion air installations shall provide an adequate supply of combustion, ventilation and dilution air determined using approved engineering methods.
G2407.9 (304.9) Mechanical Combustion Air Supply
Where all combustion air is provided by a mechanical air supply system, the combustion air shall be supplied from the outdoors at a rate not less than 0.35 cubic feet per minute per 1,000 Btu/h (0.034 m3/min per kW) of total input rating of all appliances located within the space.
G2407.9.1 (304.9.1) Makeup Air
Where exhaust fans are installed, makeup air shall be provided to replace the exhausted air.
G2407.9.2 (304.9.2) Appliance Interlock
Each of the appliances served shall be interlocked with the mechanical air supply system to prevent main burner operation when the mechanical air supply system is not in operation.
G2407.9.3 (304.9.3) Combined Combustion Air and Ventilation Air System
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.
G2407.10 (304.10) Louvers and Grilles
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 design and free area of louvers and grilles are not known, it shall be assumed that wood louvers will have 25-percent free area and metal louvers and grilles will have 75-percent free area. Screens shall have a mesh size not smaller than 1/4 inch (6.4 mm). Nonmotorized louvers and grilles shall be fixed in the open position. Motorized louvers shall be interlocked with the appliance so that they are proven to be 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 if the louvers fail to open during burner start-up and to shut down the main burner if the louvers close during operation.
G2407.11 (304.11) Combustion Air Ducts
Combustion air ducts shall comply with all of the following:
  1. Ducts shall be constructed of galvanized steel complying with Chapter 16 or of a material having equivalent corrosion resistance, strength and rigidity.
    Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one required fireblock is removed.
  2. Ducts shall terminate in an unobstructed space allowing free movement of combustion air to the appliances.
  3. Ducts shall serve a single enclosure.
  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.
  5. Ducts shall not be screened where terminating in an attic space.
  6. Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air.
  7. 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 gas-fired appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer's instructions.
  8. Combustion air intake openings located on the exterior of a building shall have the lowest side of such openings located not less than 12 inches (305 mm) vertically from the adjoining finished ground level.
G2407.12 (304.12) Protection From Fumes and Gases
Where corrosive or flammable process fumes or gases, other than products of combustion, are present, means for the disposal of such fumes or gases shall be provided. Such fumes or gases include carbon monoxide, hydrogen sulfide, ammonia, chlorine and halogenated hydrocarbons.
In barbershops, beauty shops and other facilities where chemicals that generate corrosive or flammable products, such as aerosol sprays, are routinely used, nondirect vent-type appliances shall be located in a mechanical room separated or partitioned off from other areas with provisions for combustion air and dilution air from the outdoors. Direct-vent appliances shall be installed in accordance with the appliance manufacturer's instructions.

Related Code Sections

Section G2407 Fuel Gas, (304) Combustion, Ventilation and Dilution Air
Air for combustion, ventilation and dilution of flue gases for appliances installed in buildings shall be provided by application of one ...