Combustion gas heat recovery apparatus

Claim 1

Combustion gas heat recovery apparatus for installation on an existing forced air gas or oil fired furnace having a primary heat exchanger including a gas or oil burner, a primary flue pipe for carrying heated combustion gases from said primary heat exchanger to a primary gas exhaust flue, a cold air return plenum, and a primary blower for drawing air to be heated from said cold air plenum and forcing it through said primary heat exchanger from which it is distributed within the structure heated by said furnace, said apparatus comprising: a secondary heat exchanger defining a combustion gas passage and a fresh air passage for air to be heated, which passages are isolated from one another, said secondary heat exchanger being positioned such that air drawn from said cold air return plenum is initially drawn through said secondary heat exchanger to be preheated by extracting heat from said combustion gases prior to being forced through said primary heat exchanger, said secondary heat exchanger comprising a combustion gas inlet plenum, a combustion gas outlet plenum, a plurality of heat conducting pipes sealingly connected between said inlet plenum and said outlet plenum, each of said heat conducting pipes being arranged in a serpentine pattern to define a plurality of linear radiating surfaces aligned in the direction of air flow through said heat exchanger, and heat conducting fins intimately connected to said heat conducting pipes, said primary flue pipe, said combustion gas inlet plenum and said combustion gas outlet plenum having approximately the same cross-sectional area to permit unrestricted flue gas flow; a heat recovery flue pipe connected between said primary flue pipe and said secondary heat exchanger for passing combustion gases from said primary flue pipe to said combustion gas passage of said secondary exchanger, said heat recovery flue pipe being insulated and nonintrusively connected into said primary flue pipe such that the preheating of air by said secondary heat exchanger is maximized and free access to heated combustion gases is provided, but not substantial portion of said heat recovery flue pipe extends into said primary flue pipe to thereby obstruct the normal flow of flue gases or accumulate soot and other contaminants; a cooled combustion gas exhaust pipe connected between said combustion gas outlet plenum of said secondary heat exchanger and the outside of said structure for passing cooled combustion gases from said secondary heat exchanger to the outside of said structure. a secondary blower coupled to said exhaust pipe and operable to draw heated combustion gases from said primary flue pipe through said heat recovery flue pipe and secondary heat exchanger, and to exhaust cooled combustion gases received from said secondary heat exchanger to the outside of said structure through said exhaust pipe; and condensate drainage means coupled to said secondary heat exchanger for draining condensate formed within said combustion gas heat recovery apparatus, said condensate drainage means comprising interconnected taps along the lower extremities of said heat conducting pipes and a condensate trap to permit condensate to drain from said secondary heat exchanger but prevent air or other fluids from being drawn into said apparatus.