Abstract: A forced-air furnace for burning gas or fuel oil or waste oil utilizes relatively few components and effectively heats air for space-heating purposes. The furnace includes a substantially enclosed, elongated housing having an air intake and an air discharge vent and a hollow elongated heat exchanger/combustion chamber which is supported within so as to extend axially along the housing. The furnace also includes a fuel burner assembly supported at the discharge end of the housing for directing a flame and attending combustion products directly into the heat exchanger so that the inner surface thereof absorbs heat generated thereby and so that no part of the flame impinges upon the heat exchanger. Heat transfer from the combustion products to the heat exchanger is enhanced by a pair of removable platen-like baffles mounted within the heat exchanger.