M-411.1 Location: Direct gas-fired makeup air heaters and direct gas fired industrial air heaters shall be installed only in storage facilities, factor and industrial occupancies, public garages, commercial laundries and dry cleaners and commercial kitchens. Direct gas fired air heating equipment shall not serve sleeping rooms. Direct gas fired industrial air heaters shall not be utilized in hazardous locations or where exposed to substances that are made toxic by exposure to flames.

M-411.2 Approval: Direct gas fired air heating equipment shall be labeled and shall be installed in accordance with the manufacturer's installation instructions.

M-411.3 Relief openings: Relief air openings or exhaust systems or both shall be provided and designed to provide the required air flow through the direct gas fired air heating equipment. Motorized dampers and exhaust systems provided for this purpose shall be interlocked with the direct gas-fired equipment to prevent operation of the equipment when the dampers are closed or the exhaust system is inoperative.

M-411.4 Makeup air heaters: Direct gas fired makeup air heaters shall not convey air other than outdoor air.

Exception: Air that is introduced into the system downstream of the combustion zone shall be outdoor air or indoor air.

M-4114.4.1 Intake openings: Where provided with dampers, outdoor air intake openings utilized with direct gas-fired makeup air heaters shall be interlocked with the heater to prevent heater operation when the dampers are closed.

M-411.5 Industrial air heaters: Where direct gas fired industrial air heaters are utilized in any space, such space shall be provided with outdoor ventilation air at a rate of not less than 4 cfm for each 1000 Btuh of rated input of the heater. The ventilation air supply system and all motorized dampers shall be interlocked with the heater to prevent heater operation when the dampers are closed or the outdoor supply system is inoperative.