The Series 'HAC - F' Ventilation Air Flue Damper, is designed to save energy by stopping the escape of warm air up the chimney vent while the heating appliance is not firing and is interlocked to be open during firing. Nylon bearings and all wiring are mounted 1" away from the heated part of the damper to prevent the effects of excess heat. These dampers are also designed for years of trouble free service.