Abstract: A ventilation control system is disclosed for a building having an elongated ceiling vent opening, the system having a vent door, spaced apart brackets pivotally supporting the door on the building structure adjacent to the ceiling vent opening such that the door is movable between closed and opened positions, and an actuating mechanism for moving the door between the closed and opened positions. The vent door has an elongated door casing of plastic material having a hollow interior and opposite side walls, a support member located in the hollow interior of the door casing adjacent to each of the opposite side walls and a foam material substantially filling the hollow interior of the door casing. The door casing may be extruded from plastic material and has integrally formed outwardly extending sealing members which engage the building structure when the vent door is in the closed position to seal the vent opening.