Abstract: A thermally actuated damper for insertion in the flue pipe of furnaces consists of a cylindrical section of pipe having a diametrically extending bar fixed across its interior. The bar supports a pair of identical, semi-circular vanes formed of a bi-metallic laminate which project in a common direction from the bar. When the furnace is operating the hot flue gases cause the vanes to bend into abutment with one another so that they extend longitudinally along the flue pipe and allow substantially unrestricted flow of vent gases. When the furnace is off the cooling blades bend outwardly, toward the walls of the flue pipe, substantially blocking the flow of gases through the flue so that the warm air from the heated space is not drawn up the flue.

Abstract: An automatic vent damper control mechanism for use on furnaces or the like having a spring loaded open position and an electric motor which drives it to a closed position, against the spring bias, via a gear train. A unique over-travel mechanism is provided which prevents damage to the gear train from occurring when the damper reaches the end of its travel towards its open condition.

Abstract: An automatic vent damper for combustion devices such as furnaces which closes the combustion chamber exhaust vent when the furnace burner is off to conserve heat and prevent backdrafts. A damper blade pivotally mounted in the exhaust vent is closed by an electrically-operated damper motor operating against a torsional spring urging the damper plate into the open position, the damper motor being energized whenever burner operation is not in demand by the automatic controls. When the controls call for burner operation, the motor is deenergized and the damper blade moves to the open position under the influence of the torsional spring. A limit switch senses the damper blade achieving the open position and enables burner operation.

Abstract: In a fuel-burning device having a combustion chamber, a burner with a control, an exhaust stack connected to said chamber, an air diverter in said stack and a thermostat connected to said burner control; the improvement which comprises a damper section in the stack downstream of the diverter. The damper is disposed within and journalled upon bearings attached to the damper section. A motor on the damper section has an output shaft connected to the damper and includes a rotary switch on said shaft. An electrical circuit includes a relay switch interconnecting the thermostat, burner control, motor and rotary switch. The motor output shaft is intermittently rotatable through successive arcs of 90.degree., through 360.degree., whereby the damper normally closes the stack preventing escape of room air therethrough when the burner is not operating. The thermostat, when calling for heat, closes the circuit to the motor rotating the damper 90.degree. to open position and successively energizing the burner.