Abstract: An uninterruptible gas-fired forced hot air furnace utilizes a thermoelectric generator in the path of the hot combusted gas to a heat exchanger. The combusted gas (combustion products) flows through the pipes of the heat exchanger to an exhaust which may lead to the chimney,or direct vent, in the building in which the furnace is located. The thermoelectric generator is also in the path of the forced cold air which also goes to the heat exchanger. The cold air thus picks up heat in the process of cooling the cold junctions of the thermoelectric generator and picks up more heat in the heat exchanger from the combustion products before being ducted into the heating system. The thermoelectric generator cold junctions may be air-cooled by fins connected thereto through which the stream of air from the blower passes or the cold junctions may be cooled by liquid which is circulated through a liquid-to-air heat exchanger.