Abstract: A heat exchanger unit (20) is provided to be placed upon a fireplace floor (17) and attached to a heatalator or heat form (57) to enhance the heating efficiency of a conventional fireplace. The unit receives room air through apertures (33) in its front wall (21) and conducts the cool air through a plurality of upwardly angled tubes (40) toward the rear wall (25) of the unit as the air is continuously heated by the surrounding kindling wood (18), charcoal and ashes. Mounting holes (41) are provided on the rear wall of the unit in order to attach the heat exchanger to the rear wall (13) of the fireplace. Grate holes (30) are positioned along the bottom wall and are capable of being aligned with a plurality of shaker holes (52) formed in at least one shaker grate (51) slidable over the bottom wall which is positioned in at least one elongated aperture (37) formed in the front wall.