GFD Mechanical Flue Dampers close when the appliance is not in use to prevent conditioned air from escaping through the chimney, and open right before the appliance burner fires up. This damper is controlled with the MUC or H100 series controllers from KW, and is intended to be used on gas-fired appliances with the RSD fan from KW. The GFD dampers can save up to 4000 kWh per year by preventing the loss of conditioned air, and pay for themselves with the savings! The GFD is available with an integrated RSD fan adaptor. The GFD Dampers are constructed of 316L stainless steel and listed to UL378 – Standard for draft equipment, rated up to 550ᵒF.