As of 2015, furnaces with a capacity of 50,000 British thermal units can be purchased from National Air Warehouse and HD Supply. Rheem furnaces are offered by National Air Warehouse, while HD Supply offers both DuroGuard and Williams furnaces.
National Air Warehouse offers eight models of Rheem furnaces with a capacity of 50,000 BTUs. These models vary based on size, price, and whether they are designed for upflow or downflow air circulation. The DuroGuard furnace sold by HD Supply offers upflow or side-to-side air circulation with a capacity of 50,000 BTUs. HD Supply also offers the Williams top-vent furnace with a capacity of 50,000 BTUs.