The FAMCO BD butterfly backdraft damper is used as a back draft damper for heat exchangers, exhaust systems, solar heating systems and other intake or exhaust applications where a powered damper is not needed. This damper works in both horizontal or vertical positions and the foam seal provides minimal air leakage. Due to its unique design and aluminum blades, it opens easily with normal air flow and closes with gravity. Quality constructed galvanized steel with 28 to 22 ga.