The Cape Backdraft Damper is an in-line, one way air flow valve. It opens and closes with minimal pressure in either direction. It does not rust nor require any maintenance.The Cape Backdraft Damper is silent, produces no metal clanging sounds, is tested to UL723 standards and can be installed in horizontal or vertical ductwork.
This item fits inside a duct having a 7-inch diameter. Since this product is normally installed inside the exterior walls of a heated building, extreme outside cold/humidity does not affect its efficiency.