Abstract: In a flue damper control system, a thermistor 64 responsive to flue temperatures upstream of the damper 12 is incorporated in a trigger circuit for a triac 52 which controls energization and deenergization of the damper motor 17, the damper motor being fully energized only when the flue temperature is below a predetermined value and there is no demand for heat by the thermostat 36.

Abstract: For a vent or flue damper of the type in which the damper is closed by an electrically energized actuator when the furnace is off and the actuator has first biasing means to open the damper when the actuator is deenergized, a second biasing means such as a torsion spring, independent of the first biasing means, is associated directly with the damper shaft and is adapted to always move the damper to an open position in the absence of the actuator.

Abstract: For an automatic flue damper assembly of the type in which the motor of a clockwork mechanism is energized to hold the damper closed and the mechanism is mechanically biased to move the damper to an open position in the absence of motor energization, a stopping or braking arrangement is provided which applies DC to the motor for dynamic braking as the damper closely approaches its open position. Additionally, the remote possibility of a damper hang-up at an intermediate position resulting from a residual magnetic locking torque is substantially eliminated through the provision of an AC trickle circuit connected to the motor.

Abstract: A relatively simple automatic mechanical flue damper is provided by a damper plate having a slot extending across a major portion of its diameter with a helically-shaped, temperature responsive bimetal having one end attached to the damper plate at one end of the slot, and its other end attached to a bushing which in turn is fixed relative to the flue in which the damper is situate, with a shaft extending in rotatable relation through a bore in the bushing and having its end opposite the bushing attached to the damper plate, the helical bimetal being responsive to changes in flue gas temperature to rotate the damper plate between predetermined open and closed positions with the shaft rotating to corresponding positions, and at least one of the shaft ends including indicia means to permit observation of shaft and damper rotative position.