Solid fuel warm air furnace

A furnace comprising a housing, a firebox disposed internally of and spaced from the walls of said housing, an open grate disposed at the bottom of said firebox, a door in the front of said housing for inserting solid fuel into said firebox, means for delivering combustion air to an area beneath said grate for preheating and causing said air to pass upwardly through said solid fuel and to mix with gases released from said fuel during combustion, a burn-out chamber between said firebox and the rear of said housing and insulated from said firebox, said burn-out chamber having an inlet communicated with said firebox and an outlet communicated with a heat exchanger chamber, exhaust means connected to said heat exchanger chamber for drawing said air/gas mixture from said firebox through said burn-out chamber to said heat exchanger chamber and out said exhaust means, and means at said burn-out chamber inlet and heated by heat in the firebox for igniting said air/gas mixture, said igniting means being operable to retain the flame from ignition of said air/gas mixture, whereby to promote complete combustion of said air/gas mixture in said burn-out chamber.