The Field Controls 46487201 GVD-7 is a 7-inch automatic gas vent damper designed to improve the energy efficiency of gas-fired HVAC heating systems, including boilers and furnaces. Operating on 24V power, it automatically opens during a heating cycle to allow safe exhaust of flue gases and closes when heating stops, reducing heat loss and cold-air infiltration. Constructed from corros... https://www.partshnc.com/46487201-field-controls-7-gvd-7-ventdamperlessharness