Abstract: A forced air heater for heating a venting air stream including an outer casing, a fan for forcing the venting air stream through the casing, a combustion drum providing a combustion chamber for a burner supported within the casing, a flue gas header spaced downstream from the drum connected in separate fluid communication with the combustion chamber to accommodate evacuation of combustion gases from the chamber through the header, a passage for the venting air stream extending through the casing in heat transfer relation with the drum and header, and a plurality of vanes secured within the casing adapted to circulate a predetermined portion of the venting air stream between said drum and header.