506.2 Indoor Combustion Air — 2025 California Plumbing Code
California Plumbing Code (Title 24, Part 5) · 2025 edition · updated 2026-10-19 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Plumbing Code (Title 24, Part 5) § 506.2 · Effective January 1, 2026 · Official source: Building Standards Commission
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] 506.2.1 Standard Method. The minimum required volume shall be 50 cubic feet per 1000 British thermal units per hour (Btu/h) (4.83 m [3] /kW). [NFPA 54:9.3.2.1]
506.2.2 Known Air Infiltration Rate Method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows [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)]
I other
Required Volume other ≥ [21 ft] ACH [3] 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)]
15 ft [3] I
fan
Required Volume fan ≥ ACH 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)
Required Volume other ≥ [21 ft] [3]
ACH
(
I other
[21 ft] [3]
ACH 1000 Btu/h
( )
15 ft [3] Required Volume fan ≥ ACH
(
15 ft [3] I
fan ACH 1000 Btu/h FIGURE 506.3
( )
ALL COMBUSTION AIR FROM ADJACENT INDOOR SPACES
THROUGH INDOOR COMBUSTION AIR OPENINGS
[NFPA 54: FIGURE A.9.3.2.3(1)]
For SI units: 1 cubic foot = 0.0283 m [3], 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 Equation 506.2.2(1) and Equation 506.2.2(2).
[NFPA 54:9.3.2.2(3)]
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