External flue heat exchangers

Abstract

A heat exchanger is mounted external to a section of flue pipe or is an integral part of a section of flue pipe. The heat exchanger preheats a domestic hot water supply and boosts the return water temperature prior to reentry to the furnace coil. The heat exchanger reduces fuel use, pollution and wear of the furnace and burner. A typical heat exchanger installation includes an oil or gas burner located on a furnace or boiler having a flue pipe leading to a gaseous outlet, such as a masonry chimney. A short vertical flue section leads to a draft-regulating damper. The flue heat exchanger may be a coil of copper tubing wrapped around flue section, such that the tubing picks up heat from the heated flue gasses. The cold water source is coupled to a short length of convoluted flexible tubing with coupling flanges which couple the water through the flue mounted heat exchanger. Preheated water exits from the heat exchanger through flexible tubing having a safety pressure relief valve.

I claim:  
     
         1 . A heat exchanger for preheating domestic water comprising a hollow tubing having a water inlet end and a water outlet end, said hollow tubing external to and wrapped around a section of a flue pipe of a furnace.  
     
     
         2 . The heat exchanger as in  claim 1  further comprising a pressure relief valve coupling one end of said relief valve to the water outlet end of said hollow tubing.  
     
     
         3 . The heat exchanger as in  claim 2  further comprising an isolation valve coupling said relief valve to a boiler hot water coil intake.  
     
     
         4 . The heat exchange as in  claim 2  further comprising an automatic feeder coupling said relief valve to a boiler hot water coil intake.  
     
     
         5 . The heat exchanger as in  claim 1  wherein said heat exchanger further comprising a second heat exchanger connected in series therewith and wrapped around and external to another section of flue piping, further increasing water temperature prior to entering the furnace hot water coil.  
     
     
         6 . The heat exchanger as in  claim 1  wherein said heat exchanger is prefabricated as a standard flue section, which substitutes for a length of said flue pipe, said pre-fabricated heat exchanger having a central flue pipe section with heat exchanger tubing wrapped around its periphery, said pre-fabricated heat exchanger further having encasement over said heat exchanger tubing.  
     
     
         7 . The heat exchanger as in  claim 6 , wherein said encasement permanently encloses said tubing, said encasement has a cavity and heat resistant end caps, said encasement also having a plurality of openings sufficient for a water outlet and water inlet to protrude therefrom, said cavity having a highly heat conductive material packed therein.  
     
     
         8 . The heat exchanger as in  claim 6 , wherein said encasement comprises a preformed semi-pliable sleeve, said sleeve having two edges having clasps that when brought together close said sleeve and enclose said tubing forming a plurality of holes sufficient for said water inlet and said water outlet to protrude therefrom.  
     
     
         9 . The heat exchanger as in  claim 7  wherein said encasement includes a thermal insulator between said encasement's inner surface and the heat conductive material.  
     
     
         10 . The heat exchanger as in  claim 9  wherein said thermal insulator is a fiberglass liner.  
     
     
         11 . The heat exchanger as in  claim 1  wherein said heat exchanger is a hydronic heating system using fin tube heating elements, said heat exchanger having a hydronic loop circulated by a circulator pump forcing water into a heating coil inside the boiler then leading to an expansion tank and further to an arrangement of zone valves through fin tube baseboard hot water room sections and then through a return manifold.  
     
     
         12 . The heat exchanger as in  claim 1  wherein said heat exchanger coil is wrapped around a cylindrically shaped sheet of conductive metal, said cylinder having three quarters of its circumference affixed to a corresponding area of coil, which said sheet is slightly larger in diameter than a section of said flue pipe, said sheet having a small gap along its length, said gap allowing said flue section to slide into said cylinder, said cylinder further comprising a locking means to secure said cylinder when said gap is closed.  
     
     
         13 . The heat exchanger as in  claim 12  wherein said cylindrical sheet is copper, said cylinder also having gaskets on the inner and outer periphery of said cylinder sufficient in size to prevent contact with flue pipe sections made from a different type of metal.  
     
     
         14 . The heat exchanger as in  claim 1  further comprising a pair of interleaved flue heat exchanger coils wrapped together around said flue pipe, said coils comprising two separate conduits for separate transfer of heated water therethrough.  
     
     
         15 . The heat exchanger for a domestic source of heat having a flue pipe leading to a masonry chimney, comprising: 
 a coil of heat conductive tubing wrapped around a section of said flue, said coil picking up heat from the heated flue gasses wherein said flue section is made of copper, said flue section further having gaskets located on respective inner and an outer edge peripheries, thereby preventing direct contact with flue sections made from metal other than copper.    
     
     
         16 . The heat exchanger as in  claim 15  wherein a cold water source is coupled to a length of convoluted flexible tubing having coupling flanges at either end, wherein said coupling flanges allow water transport to and from said heat exchanger.  
     
     
         17 . The heat exchanger as in  claim 16  wherein the preheated water from said heat exchanger is coupled to a boiler hot water coil intake.  
     
     
         18 . The heat exchanger as in  claim 17 , wherein the preheated water from said heat exchanger is also coupled to a domestic supply pipe.  
     
     
         19 . The heat exchanger as in  claim 15  further comprising a pressure relief valve.  
     
     
         20 . A heat exchanger for preheating domestic water comprising a hollow tubing having a water inlet end and a water outlet end, said hollow tubing external to and wrapped around a section of a flue pipe of a furnace, 
 said heat exchanger is prefabricated as a standard flue section, which substitutes for a length of said flue pipe,    said pre-fabricated heat exchanger having a central flue pipe section with heat exchanger tubing wrapped around its periphery,    said pre-fabricated heat exchanger further having an encasement over said heat exchanger tubing, said encasement enclosing said tubing,    said encasement having a cavity and heat resistant end caps, said encasement also having a plurality of openings sufficient for a water outlet and water inlet to protrude therefrom, said cavity having a highly heat conductive material packed therein,    said encasement comprising a preformed semi-pliable sleeve, said sleeve having two edges having clasps that when brought together close said sleeve and enclose said tubing forming a plurality of holes sufficient for said water inlet and said water outlet to protrude therefrom, and,    said encasement including a thermal insulator between said encasement's inner surface and the heat conductive material.