511.3 Makeup Air — 2025 California Mechanical Code

The makeup air quantity shall prevent negative pressures in the commercial cooking area(s) from exceeding 0.02 inch water column (0.005 kPa). Where the fire-extinguishing system activates, makeup air supplied internally to a hood shall be shut off.

For compensating hoods, where a Type I or Type II hood has an internal discharge of makeup air, the makeup air flow shall not exceed 10 percent of the exhaust airflow, the exhaust airflow shall be the net exhaust from the hood in accordance with Section 508.5.1.2 through Section 508.5.1.5. The total hood exhaust shall be determined in accordance with Equation 511.3.

E NET = E HOOD – MA ID (Equation 511.3)

Where:

E NET = net hood exhaust, CFM (L/s)

E HOOD = total hood exhaust, CFM (L/s)

MA ID = makeup air, internal discharge, CFM (L/s)

For SI units: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per

minute = 0.4719 L/s

511.3.1 Air Balance. Design plans for a facility with a commercial kitchen ventilation system shall include a schedule or diagram indicating the design outdoor air balance. The design outdoor air balance shall indicate the exhaust and replacement air for the facility and the net exfiltration where applicable. The total replacement airflow rate shall equal the total exhaust airflow rate and the net exfiltration.