Flexible air ducts, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such ducts shall be listed and labeled as Class 0 or Class 1 flexible air ducts and shall be installed in accordance with Section 304.1.
Flexible air ducts shall not be limited in length.
Flexible air connectors, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such connectors shall be listed and labeled as Class 0 or Class 1 flexible air connectors and shall be installed in accordance with Section 304.1.
Flexible air connectors shall be limited in length to 14 feet (4267 mm).
Flexible air connectors shall not pass through any wall, floor or ceiling.
The design temperature of air to be conveyed in flexible air ducts and flexible air connectors shall be less than 250°F (121°C).