504.3 Domestic Cooking Exhaust Equipment — 2025 California Mechanical Code

Domestic cooking exhaust equipment shall comply with the following requirements, as applicable:

(1) The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall comply with UL 507.

(2) Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.

(3) Domestic cooking appliances with integral downdraft exhaust equipment shall comply with UL 858 or CSA/ANSI Z21.1/CSA 1.1.

(4) Microwave ovens with integral exhaust for installation over the cooking surface shall comply with UL 923.

(5) All domestic kitchen exhaust ducts used in conjunction with domestic range or cooktop hoods shall be constructed of metal and shall have smooth interior surfaces, fastened and sealed with duct mastic or metal tapes that meet the requirements of UL 181A.

Exception: Ducts for domestic kitchen downdraft grillrange ventilation installed under a concrete slab floor shall be permitted to be of approved Schedule 40 PVC provided the following conditions are met:

(1) The under-floor trench in which the duct is installed shall be completely backfilled with sand or gravel.

(2) Not more than 1 inch (25.4 mm) of 6 inch diameter (150 mm) PVC coupling shall be permitted to protrude above the concrete floor surface.

(3) PVC pipe joints shall be solvent cemented to provide an air and greasetight duct.

(4) The duct shall terminate above grade outside the building and shall be equipped with a backdraft damper.

(6) Range hoods shall discharge to the outdoors through a single wall duct and shall not terminate in an attic or crawl space.