Field Controls GVD Automatic Gas Vent Damper, 4 in, 24 VDC, 60 Hz
Field Controls Gas Vent Damper, Automatic, Series: GVD, 24 VDC, 60 Hz, 4 in Damper, Round, 6-1/16 in L x 8-7/8 in W
The Field Vent Damper works automatically to allow natural draft during appliance operation while preventing residual appliance heat and conditioned air from escaping during off cycles. It also prevents the infiltration of cold air during down drafts. It's made of stainless steel and is available in 8 sizes, 4 in through 10 in and 12 in.