Abstract: A fireplace heating unit is disclosed which will efficiently heat the interior of a structure. The unit includes a firebox surrounded by a housing. The housing is vented to the outside at the rear thereof and to the interior of the structure at the front thereof, over the firebox. Exterior air is drawn into the housing through the rear vent and circulated around the firebox and through conduits extending through the chimney flue whereby it is quickly heated. The heated air is then exhausted into the room through the front vent. A portion of the front of the housing may mount a movable glass door having a controlled air inlet therein to control combustion of fuel in the firebox. The door also provides access to the firebox and may be opened to permit use of the firebox as a conventional fireplace, if desired. In one embodiment a zero clearance unit is provided, having a novel bypass to divert at least a portion of the flow of heated air from the interior of the housing into the flue.