506.4 Outdoor Combustion Air — 2025 California Plumbing Code

Outdoor combustion air shall be provided through opening(s) to the outdoors in accordance with the methods in Section 506.4.1 or Section 506.4.2. The minimum dimension of air openings shall not be less than 3 inches (76 mm). [NFPA 54:9.3.3] 506.4.1 Two Permanent Openings Method. Two permanent openings, one commencing within 12 inches

FIGURE 506.4.1(1)

ALL 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)

ALL COMBUSTION AIR FROM OUTDOORS

THROUGH VENTILATED ATTIC

[NFPA 54: FIGURE A.9.3.3.1(1)(b)]

FIGURE 506.4.1(3)

ALL COMBUSTION AIR FROM

OUTDOORS THROUGH HORIZONTAL DUCTS

[NFPA 54: FIGURE A.9.3.3.1(2)]

FIGURE 506.4.2

ALL COMBUSTION AIR FROM OUTDOORS THROUGH

SINGLE COMBUSTION AIR OPENING

[NFPA 54: FIGURE A.9.3.3.2]

(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 m [2] /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 m [2] /kW) of total input rating of all appliances in the enclosure. [NFPA 54:9.3.3.1] [See Figure 506.4.1(3)] 506.4.2 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 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 m [2] /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]