An automatic temperature and pressure responsive damper assembly for use within the conduit of a ventilating system designed to exhaust the air from a confined space to the atmosphere when the confined space reaches a preselected temperature or when the pressure in the confined space is greater than that in the conduit adjacent to the atmosphere. The damper assembly includes at least one vane pivotally mounted within the conduit, preferably two, the vane or vanes being mounted so that they are movable between a generally opened position, wherein air can pass freely through the conduit, and a generally closed position, wherein air passage through the conduit is blocked. A temperature responsive drive assembly that detects the temperature within the conduit is mounted therein and acts upon the vane or vanes is provided such that a change in temperature and expansion of the temperature responsive drive assembly causes the vanes to move to their opened position. Biasing means are provided for urging the vane or vanes when subjected to the aforementioned differential in pressure to their normally closed position.