These gas wall and ceiling heaters suspend from a bracket or threaded rod to save limited floorspace. They provide intermittent or continuous heating in large areas, such as factories, warehouses, stock rooms, service stations, and garages. They use a forced air system that uses a heat exchanger and fan or blower to push heated air into a space. These units are field-convertible from open to separated combustion. The open combustion configuation pulls air from the immediate area around the heater into the combustion chamber. The separated combustion configuration allows air from outside the room to be brought into the combustion chamber and is ideal for dusty, dirty, and mildly corrosive conditions as well as areas with high humidity or slightly negative pressures.