Air Conditioner Accessories
A damper opens automatically when the furnace blower comes on, and closes when the furnace blower turnoff. When the furnace is not in use, the damper keeps air from the ductwork from coming inside the furnace. A damper is often used when separate A/C units don't require use of the furnace blower. A 12" x 12" minimum opening in the duct is needed to use a damper; its total size is 17.5" x 18".