Section R. 400.18656 - Air-conditioning and air-handling systemsRule 656.
(1) If power exhaust ventilation is to be used, there shall be an air supply equal to the amount exhausted, especially in areas that house combustion equipment.(2) Fan and air-handling equipment used for recirculating air in more than 1 room or a single area shall be located in a room that is cut off from other portions of the building by construction that has not less than a 1-hour-fire-resistance rating. A room that houses fans and air-handling equipment shall not be used for any combustible storage.(3) A duct or plenum which employs mechanical means for the movement of air and which is used for heating and ventilation, including warm air heating systems, plain ventilating systems, air-conditioning systems, or exhaust systems, shall be constructed entirely of noncombustible material. If a duct or plenum of an existing system is constructed, wholly or in part, of combustible materials, it shall be reconstructed entirely of noncombustible materials, if possible. If revamping or reconstruction is impractical due to design or construction, the inspecting authority may accept the existing installation if heat-actuated fire dampers are installed in each return air duct opening from every room or space.
(4) A heat-actuated fire damper shall be installed on the discharge side of each recirculating fan unit that serves more than 1 room or a single area and, where practicable and feasible, there shall be an approved thermostatic device that has a setting of not more than 125 degrees Fahrenheit located in the system at a suitable point in the return air duct ahead of the fresh air intake, actuation of which shall open the electrical circuit that supplies the fan motor. If it is impracticable to locate a thermostatic device ahead of the fresh air intake, an approved heat or smoke-actuated device, actuation of which will open the electrical circuit that supplies the fan motor, shall be located at a suitable point in the air duct on the discharge side of the fan.(5) If an existing system utilizes corridors or exitways as return air plenums, the system shall be revamped to eliminate the utilization of corridors or exitways as return air plenums. If revamping is impractical due to design or construction, the inspecting authority may accept the existing system if an approved smoke detector is installed in each separated area of the corridors or exitways to automatically open the electrical circuit that supplies the fan motor. A smoke detector shall incorporate visual or audible signals to indicate any trouble that would interfere with the proper operation of the smoke detector. A stairway shall not be used as a return air plenum.Mich. Admin. Code R. 400.18656