Automatic stack damper

In a system comprising a heat stack, a damper having a vane in said heat stack, actuating means for opening and closing said damper, said actuating means electrically connected to and responsive to a first thermostat in an electrical circuit containing a heating means for generating heat, the by-products from which pass through said stack, the improvement wherein said actuating means comprises an electric motor spring biasedly connected to said vane, said electric motor in an "On" position having current passing therethrough and holding said vane, against the action of said spring, in a closed position, and means responsive to the closing of said thermostat for deactivating said motor, said means responsive to the closing of said thermostat comprising a coil in the electrical circuit containing said thermostat which is energized upon closure of said thermostat which throws a first relay switch in a second circuit containing a second coil, which coil is energized upon completion of the second circuit containing said first relay switch, said second coil connected to a normally closed relay which is opened upon energization of said second coil, said second relay being in the electrical circuit of said electric motor, whereby when said second relay is open, the circuit of said motor is broken and the output shaft of said electric motor rotates.