502.2 Termination of Exhaust Ducts — 2025 California Mechanical Code

Exhaust ducts shall terminate in accordance with Section 502.2.1 through Section 502.2.4. Classes of air shall be as defined in Section

203.0 and classified in Section 403.9.

502.2.1 Environmental, Class 1, and Class 2 Air Ducts. Environmental, Class 1, and Class 2 air duct exhaust shall terminate not less than 3 feet (914 mm) from a property line, 10 feet (3048 mm) above a public way, 3 feet (914 mm) from openings into the building and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1. The discharge of dryer exhaust ducts shall not terminate over a public way or over an area where condensate or vapor could create a nuisance or hazard.

502.2.2 Class 3 Air Ducts. Class 3 air duct exhaust shall terminate not less than 10 feet (3048 mm) from a property line, 3 feet (914 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 10 feet (3048 mm) from openings into the building, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.

502.2.3 Product Conveying, Flammable, and Class 4 Air Ducts. Ducts conveying Class 4 air or explosive or flammable vapors, fumes, or dusts shall terminate not less than 30 feet (9144 mm) from a property line, 10 feet (3048 mm) from openings into the building, 6 feet (1829 mm) from exterior walls or roofs that are in the direction of the exhaust discharge, 30 feet (9144 mm) from combustible walls or openings into the building that are in the direction of the exhaust discharge, 10 feet (3048 mm) above adjoining grade, and the minimum separation distance from ventilation system outdoor air intakes determined in accordance with Section 402.4.1.

Exception: Type I Hood exhaust termination shall be in accordance with Section 510.9.

EXHAUST SYSTEMS

tem in accordance with Section 505.7.3 do not require design as Class 1 product-conveying ducts.

Exceptions:

(1) Ductless range hoods where installed in accordance with the manufacturer’s installation instructions.

(2) Condensing clothes dryers where installed in accordance with the manufacturer’s installation instructions.

504.1.1 Backdraft Protection. Exhaust ducts shall terminate outside the building and shall be equipped with backdraft dampers or with motorized dampers that automatically shut where the systems or spaces served are not in use. [OSHPD 1, 1R, 2, 4 & 5] Exception: Back- draft dampers are not required when the exhaust fan must operate continuously.

Exception: Where the exhaust duct does not discharge into a common exhaust plenum and one of the following:

(1) The exhaust fan runs continuously.

(2) The exhaust duct serves space(s) that are not mechanically heated or cooled.

(3) The space served is maintained at positive pressure.