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: In a fan mounting arrangement in which a centrifugal fan housing has slide rails which are received in tracks of the fan base plate, the housing has an inclined flange along the edge of the fan discharge opening which leads as the housing is being installed, this flange being elevated by ramp means on the track as the housing approaches its final position so that the flange clears the edge of the opening in the fan base plate and pulls up the leading end of the fan housing for reducing air leakage between the fan housing discharge opening and the fan base plate. Additionally, the slide rails are provided with ramping means adjacent the trailing edge to elevate the trailing edge of the fan housing as it approaches its final position. The slide rails are fastened to the base plate after the fan housing is in its fully slid-in position, to prevent sliding of the housing relative to the base plate and also to insure the fan housing is pulled up tightly to the base plate.

Abstract: A pair of strips having spaced cutouts therein are placed in lapping relation so the cutouts form openings to receive insulating bushings having circumferential grooves therearound at least some of the end margins of the intervening webs between the cutouts being retroverted to take the form of barbs which in the assembled relation face corresponding barbs of the other strip.