![]() ![]() ![]() Duct systems shall be constructed of materials having a flame spread index of not greater than 200.The use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125☏ (52☌) and exposed surfaces are not subject to condensation.Galvanized steel shall conform to ASTM A653. Field-fabricated and shop-fabricated metal and flexible duct constructions shall conform to the SMACNA HVAC Duct Construction Standards-Metal and Flexible except as allowed by Table M1601.1.1.Fibrous glass duct construction shall conform to the SMACNA Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards. ![]() Factory-made ducts shall be listed and labeled in accordance with UL 181 and installed in accordance with the manufacturer's instructions.Equipment connected to duct systems shall be designed to limit discharge air temperature to not greater than 250☏ (121☌). ![]()
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