A unique heat exchanger device which is mounted in the flue of a forced air furnace is disclosed. A plurality of copper tubes are retained in a substantially parallel and equidistant relationship by means of end plates. A plurality of circular metallic fins are positioned on the copper tubes and serve as heat radiating surfaces. Cross tubes are provided within the copper tubes permitting the passage of heated air therethrough. The tube assembly is covered by a perforated shroud permitting air at room temperature to pass therethrough and to circulate among the heated copper tubes. An exhaust manifold is provided on the perforated shroud to permit connection of the device to the cold air return on the furnace.