An air inlet damper apparatus for minimizing the entrance of outside air into a poultry house when the ventilation exhaust fans are running and the radiant tube heater is not operating. The apparatus has a housing with a passage and a coupling flange; a pin that spans the passage and divides the apparatus into a low pressure side and an outside high pressure side, where the low pressure side is in fluid communication with a blower supplying combustion air to the tube heater; a damper blade connected to the pin; a stop; and a means for controlling the damper blade. The controlling means is responsive to pressure. The damper blade pivotally opens away from the stop when there is a static pressure differential that is higher than the negative pressure created by the ventilation exhaust fans, or when the controlling means electromechanically actuates the damper blade.