Abstract: A heater including a heat dump opening and a heat dump cover moveable between an open and a closed position to selectively block flow of fluid through the heat dump opening. The heat dump opening is formed in the top of the housing, and the heat dump cover is biased toward the open position. The cover moves to an open position in response to a sensed preselected limit temperature to vent excessively heated air to ambient to prevent damage to the heater and a duct system and a building to which the heater may be connected. Air escaping the heater via the heat dump opening may cause replacement air to be drawn into the heater to cool the heater, including electrical components of the heater located near an inlet and an outlet of the heater.