407.7 Unoccupied Turndown — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 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 Mechanical Code (Title 24, Part 4) § 407.7 · Effective January 1, 2026 · Official source: Building Standards Commission
407.7.1 Where indicated with a “yes” in the Unoccupied turndown column of Table 4-A, the number of air changes shall be permitted to be reduced. The following condi- tions shall be met:
(1) The number of air changes may be reduced to 25 per- cent of the indicated value in Table 4-A for pressur- ized spaces when the room is unoccupied.
(2) The number of air changes per hour indicated is reestablished whenever the space is occupied.
(3) The pressure relationship with surrounding rooms is maintained when the air changes per hour are reduced.
(4) All operating, class 3 imaging and cesarean delivery rooms shall maintain a minimum of six air changes per hour of total air when not in use.
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