Abstract: A heat exchanger comprises an outer chamber having an inlet and outlet for passing a flow of air through the outer chamber. An inner chamber is disposed within the outer chamber and has a second inlet and a second outlet for passing a flow of gas through the inner chamber. Heat exchange tubes are arranged in the inner chamber whereby the flow of gas contacts the outer surface of the tubes. A baffle device is disposed between the inner and outer chamber for directing the flow of air from the inlet, through a first section having heat exchange tubes, into the outer chamber and back into a second section having heat exchange tubes, so that air passes through the heat exchange tubes in the first and second sections.