A gas fired heating appliance comprising a chassis, a firebox having an interior cavity having a gas burner and an opening communicating the interior of the firebox with an environment external to the appliance, a door for enclosing the opening, and at least one track member. The track member has a retracted position and an elongated extended position, and also has a first end secured to the chassis or the firebox and a second end engaging the door. When in its retracted position the track member positions the door to enclose and seal the opening. When in its extended position the track member retains the door in a position outwardly off-set from the firebox adjacent the opening.