Abstract: A forced air liquid heating furnace which includes a liquid heating jacket or chamber surrounding the combustion chamber and having an exhaust gas discharge passage formed in the bottom of the combustion chamber to produce heat transfer on both sides of the liquid heating jacket formed around the combustion chamber. This furnace provides a compact unit which subjects the liquid to the maximum heat exchange output produced in the combustion chamber while maintaining the bottom sufficiently cool to prevent deterioration thereof from the high temperatures produced in the combustion chamber.