Appendix G Example Calculation of Outdoor Air Rate — 2025 California Mechanical Code
California Mechanical Code (Title 24, Part 4) · 2025 edition · updated 2026-10-19 · 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) Appendix G · Effective January 1, 2026 · Official source: Building Standards Commission
(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
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This state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.
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APPENDIX G
EXAMPLE CALCULATION OF OUTDOOR AIR RATE
The provisions contained in this appendix are not mandatory unless specifically adopted by a state agency, or referenced in the adopting ordinance.
G 101.0 Example Calculation of Outdoor Air Rate.
G 101.1 Example Calculation. Determine the outdoor air rate required for a single zone AC unit serving an interior 2000 square feet (185.81 m [2] ) conference/meeting room with a design occupancy of 100 people. The system supplies and returns air from the ceiling. (See Chapter 4 of this code for guidelines)
Solution:
In accordance with Table 403.2.2, the zone air distribution effectiveness is 1.0 since the system supplies cooling only from the ceiling. Using the rates from Table 402.1 for a conference/meeting room, the minimum system outdoor air rate is calculated to be:
RpPz + RaAz Vot = (Equation G 101.1) Ez
5 x 100 + 0.06 x 2000
= 1.0
= 620 CFM
Where:
Az = zone floor area: the net occupiable floor area of the zone in square feet (m [2] ).
Pz = zone population: The largest number of people expected to occupy the zone during typical usage. Where the number of people expected to occupy the zone fluctuates, Pz shall be permitted to be estimated based on averaging approaches described in Section 403.6.1. Where Pz cannot be accurately predicted during design, it shall be estimated based on the zone floor area and the default occupant density in accordance with Table 402.1. Rp = outdoor airflow rate (CFM) (L/s) required per person in accordance with Table 402.1 .
Ra = outdoor airflow rate required per unit area (CFM/ft [2] )
[(L/s)/m [2] ] in accordance with Table 402.1.
Ez = zone air distribution effectiveness in accordance with Table 403.2.2. For SI units: 1 square foot = 0.0929 m [2], 1 cubic foot per minute = 0.00047 m [3] /s,
1 cubic foot per minute = 0.4719 L/s, 1 cubic foot per minute per square foot
= 5.08 [(L/s)/m [2] ]
RpPz + RaAz Vot = Ez
5 x 100 + 0.06 x 2000
= 1.0
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