405.2 Ventilation Air Rate — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-25 · 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 Mechanical Code (Title 24, Part 4) § 405.2 · Effective January 1, 2026 · Official source: Building Standards Commission
The required mechanical ventilation outdoor air rate ( Qtot ) shall be as calculated in accordance with Equation 405.2.
Exception: For existing buildings and where permitted by the Authority Having Jurisdiction, the total mechanical ventilation ( Qtot ) is not required where Qtot is calculated to be less than 15 ft [3] /min (7.08 L/s).
Qtot = 0.03 Afloor + 7.5 ( Nbr + 1) (Equation 405.2)
Where:
Qtot = Total required ventilation outdoor air rate, CFM (L/s) Afloor = Floor area, ft [2] (m [2] ) Nbr = Number of bedrooms more than 1
For SI Units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
405.2.1 Reduced Ventilation Air Rate. Where permitted by the Authority Having Jurisdiction, the mechanical ventilation air rate required in Section 405.2 shall be permitted to be reduced where an infiltration rate is determined in accordance with ASTM E779.
Explained in plain English
Guides that cite this section.
Get a plain-English answer with a citation back to this text.
Ask AI about this code