506.3.1.1 Grease duct materials.
MC § 506.3.1.1
Grease ducts serving Type I hoods, and located within buildings, shall be constructed as follows: 1. Ducts with a cross-sectional area up to and including 155 square inches (1.0 square meters) shall be constructed of 0.0598-inch (1.52 mm) No. 16 Gage steel; 2. Ducts with a cross-sectional area over 155 square inches (100 000 mm 2 ), but not more than 200 square inches (0.129 m 2 ) shall be constructed of 0.074-inch (1.9 mm) No. 14 Gage steel; and 3. Ducts with a cross-sectional area equal to or more than 200 square inches (0.129 m 2 ) shall be constructed of 0.1046-inch (2.66 mm) No. 12 Gage steel. If stainless steel is used for ducts of any of the cross-sectional areas listed above, the Gage steel may be increased upwards (resulting in a smaller thickness) by 1 even Gage size. Exception: Listed and labeled factory-built commercial kitchen grease ducts shall be listed and labeled in accordance with UL 1978 and installed in accordance with Section 304.1 and as approved by the commissioner.
