Abstract: A heat exchanger having replaceable heat exchange surfaces comprises a plurality of tubes formed into a bundle wherein the tubes are arranged linearly side by side. The heat exchanger is provided with a header and reverse header at either end of the tube bundle for directing the flow of fluid therethrough. A heat exchange structure is positionable about the tube bundle in thermal contact therewith. The heat exchange structure has a surface matrix from which extend a plurality of fins for receiving heat conducted from the tube bundle. The heat exchange structure may be conveniently formed into a U-shaped sleeve which may be slid over the tubes of the tube bundle and affixed in place by means of a thermal conductive cement. The tubes may be shaped to provide a streamlined flow of a cooling fluid about the fins thereby increasing the efficiency of heat transfer to the cooling fluid.