in the present invention , an automatic flue damper located in the vent stack of a household furnace or other apparatus requiring venting is interfaced with a thermostatic control and a fuel supply valve associated with the apparatus so as to maintain a vent passage to the atmosphere normally open during times when combustion is occurring in the apparatus and to close the vent passage at an appropriate time following the termination of combustion in the apparatus . the normally open vent condition is maintained by a damper positioning spring . vent closure following combustion is accomplished by means of a direct current solenoid . further included in the interfacing circuitry are a temperature sensing device effective to disable the solenoid , thus opening the vent , upon the appearance of unsafe stack temperatures and a pressure sensor which also disables the solenoid to open the vent stack upon the occurrence of an inappropriate discharge of fuel to the combustion chamber . the pressure sensor then also sounds an alarm to alert those nearby of the unauthorized escape of fuel .