Abstract: A heat exchanger comprising a burner in a vertical heating chamber, having openings along its upper end to horizontally extending coils which pass through a plurality of heat transfer fins, the coils opening near the bottom edge of the assembly to a horizontally extending collector tube, open at one end and closed at the other. The open end of the collector tube opens to a vertical tubular stack through which outside air is blown past the opening to the collector tube thus creating a vacuum at that point to draw heated air from the heating chamber and through the coils where the heat is taken up by the heat transfer fins and transferred to air flowing through a hot air duct of a heating system in which the heat exchanger is placed. A blower connected in the bottom portion of the vertical stack draws outside air into the stack through an intake conduit at the bottom end and out through an exhaust conduit at the upper end of the stack.