High efficiency heat return fireplace

Claim 1

A fireplace unit, comprising: an enclosure including a first housing and a second housing, said second housing defining a fire box for consumption of combustible material, said first housing having a first pair of oppositely opposed side walls, a back wall and a bottom wall, all connected to one another, said second housing having a second pair of oppositely opposed side walls, a back wall, and a bottom wall, the side walls, back and bottom walls of said second housing being spaced from, but generally coextensive with the corresponding walls of said first housing to delimit a heat chamber about said fire box, individual ones of the side walls and the bottom wall of said second housing being formed from a single sheet of material having a plurality of undulations formed in it, the undulations having generally alternate peaks and valleys, the undulations of said bottom wall of said second housing defining with the bottom wall of said first housing a plurality of tubular sections extending along the depth of said fire box, said tubular sections communicating with the environment of said fireplace unit on one end and with said heat chamber on another end along the back walls of said first housing and said second housing: a plurality of pipes extending along an upper end of said fire box and communicating with said heat chamber and the room environment of said fireplace so as to provide an air flow path from said room through said tubular sections to said heat chamber, and from said heat chamber through said plurality of pipes to said room, the heat chamber about said fire box enabling air in said air flow path to be heated from said fire box along the opposed side walls, back wall and bottom wall of said second housing, while said pipe plurality permits heating of air in said air path along the upper end of said fire box; flue means connected to said fire box to conduct hot gases from said fire box past said plurality of pipes and to the atmosphere; means for controlling air input to said heat chamber; and means for controlling air output from said plurality of pipes.