Abstract: An automatic vent damper and fuel valve control for a fluid fuel-fired furnace including an electrically-operated valve in the fuel line, a normally-open damper in the furnace vent having electrically-operated means for closing the damper, and a thermostat for sensing the temperature in the space being heated. A Hall-effect generator is employed for sensing the positions of the damper and for respectively providing signals in response thereto. A gas detector is provided for sensing the presence of hydrocarbon-containing gas in the region of the draft hood and vent of the furnace and for providing a gas-present signal in response thereto. A control is provided for the valve responsive to both the damper-open signal and the thermostat calling for heat to energize the valve to open the same, the valve control de-energizing the valve to close the same in response to the thermostat calling for termination of heating, or the damper-closed signal, or the gas-present signal.