603.11.1 Air duct at heat sources.
MC § 603.11.1
Where heat sources from electrical equipment, fossil fuel-burning equipment, or solar energy collection equipment are installed in air ducts, the installation shall avoid the creation of a fire hazard. Air ducts rated as Class 1 in accordance with UL 181, air duct coverings, and linings shall be interrupted at the immediate area of operation of such heat sources in order to meet the clearances specified in the equipment listing. Exceptions: 1. Appliances listed for zero clearance from combustibles where installed with the conditions of their listings.
2.Insulation specifically suitable for the maximum temperature that reasonably can be anticipated on the duct surface shall be permitted to be installed at the immediate area of operation of such appliances.
