506.3 Indoor Opening Size and Location — 2025 California Plumbing Code
California Plumbing Code (Title 24, Part 5) · 2025 edition · updated 2026-10-23 · 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) § 506.3 · Effective January 1, 2026 · Official source: Building Standards Commission
Openings used to connect indoor spaces shall be sized and located in accordance with the following:
(1) Combining spaces on the same story. Each opening shall have a minimum free area of 1 square inch per 1000 Btu/h (0.002 m [2] /kW) of the total input rating of all appliances in the space but not less than 100 square inches (0.065 m [2] ). One permanent opening shall commence within 12 inches (305 mm) of the top of the enclosure and one permanent opening shall commence within 12 inches (305 mm) of the bottom of the enclosure (see Figure 506.3). The minimum dimension of air openings shall not be less than 3 inches (76 mm).
(2) Combining spaces in different stories. The volumes of spaces in different stories shall be considered as 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 1000 Btu/h (0.004 m [2] /kW) of total input rating of all appliances. [NFPA 54:9.3.2.3]
FIGURE 506.3
ALL COMBUSTION AIR FROM ADJACENT INDOOR SPACES
THROUGH INDOOR COMBUSTION AIR OPENINGS
[NFPA 54: FIGURE A.9.3.2.3(1)]
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