Abstract: A heat exchanger adapted to be readily assembled and installed in an existing fireplace to recover heat which would otherwise be lost up the fireplace chimney is comprised of a plurality of upright U-shaped tubes secured together in laterally spaced relation by a rear plate removably attached across the rear, upright segments of the tubes. The heat exchanger is placed in an existing fireplace with the open front ends of the bottom and top tubular segments facing towards the front of the fireplace, and with the bottom tubular segments resting on the fireplace floor under a separate, fire grate. A manifold connected to a forced air blower may be removably connected to the forwardly facing, open front end of the bottom tubular segments of the heat exchanger to permit either forced or convection flow of air from a room through the heat exchanger tubes for heating, the heated air being expelled back into the room through the open front ends of the top tubular segments of the heat exchanger.