404.2 Average Outdoor Air Fraction — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-09-25 · California
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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) § 404.2 · Effective January 1, 2026 · Official source: Building Standards Commission
The average outdoor air fraction ( X s) for the ventilation system shall be determined in accordance with Equation 404.2.
Xs =Vou / Vps (Equation 404.2)
Where the uncorrected outdoor air intake ( Vou ) is determined in accordance with Section 403.5.1, and the system primary airflow ( Vps ) shall be determined at the condition analyzed. [ASHRAE 62.1:A1.1]
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