•20 gauge galvanized steel housing •Aluminum spring loaded butterfly damper blades •Damper seals against EDPM rubber gasket in closed position for minimal leakage •Gasket designed for use in temperatures from - 22°F to 180°F •Require from 0.04 to 0.08 inches W.G. to begin to open •May be installed in any position. (14" and 16" models require adjusting spring tension if used in vertical position, with airflow down) •Simple installation - entire assembly inserts into duct •Exterior foam gaskets assure a tight seal against interior surface of duct