A unitary furnace through which air is circulated for heating purposes is disclosed. A blower forces air through a number of heat exchange tubes horizontally positioned within the combustion chamber for space heating purposes. Another blower is provided for the delivery of air to the burning material disposed upon a fuel support frame within the combustion chamber through an air distribution manifold. The manifold is fitted within the combustion chamber and has a number of air discharge openings positioned above and below the fuel support frame. These openings are oriented and arranged to direct the air passing therethrough generally inwardly toward the fuel on the fuel support frame. An electrical circuit including temperature sensors is provided for regulating air flow from each of the two blowers. One sensor is positioned in the furnace flue outlet and the other sensor is positioned exteriorly of the furnace in the space to be heated.
