Abstract: An improved fireplace liner of the type in which air is drawn in to a heat exchange chamber to be heated before passing into the room in which the fireplace is located. A movable closure device is located between the heat exchange chamber and the outside environment. A thermally-responsive spiral-shaped member, connected to the closure device and to the heat exchange chamber, coils or winds up to open the closure device when heat is applied to the fireplace. The opening of the closure device permits the entrance of outside air into the heat exchange chamber for heating by the fireplace. The thermally-responsive member unwinds or relaxes when heat is removed from the fireplace, allowing the closure device to return to its closed position, thus preventing the introduction of outside air.