A heating unit comprising an outer shell defining a portion of the heating unit periphery, an inner shell disposed within the outer shell and defining an internal cavity, an intermediate cavity formed by the inner and outer shells, a plurality of openings in the inner shell providing air flow between the intermediate cavity and the internal cavity, a heating source, a distribution device transferring heated air from the heating source to the intermediate cavity, a plurality of ambient air vents, and wherein the heated air traverses the plurality of ambient air vents and the plurality of openings.