Patent ID: 7559293

Claim:
A water heater having improved heat exchange efficiency, said water heater comprising: a water tank having an upper surface and a bottom surface, the water tank being configured to store water to be heated and to permit circulation of water throughout an interior of the water tank; a flue system positioned to extend between said upper surface and said bottom surface of said water tank through the interior of said water tank and to transfer heat from combustion products within said flue system to water in said water tank, said flue system including: an upstream heat exchange portion having at least one substantially vertical flue tube and a downstream heat exchange portion having a plurality of substantially vertical flue tubes, said upstream heat exchange portion of said flue system providing a first pass for heat exchange with water in said water tank and said downstream heat exchange portion providing second and third sequential passes for heat exchange with water in said water tank, each of said first pass, said second pass, and said third pass extending between said upper surface and said bottom surface of said water tank, and each of said second and third sequential passes having a plurality of said flue tubes, said upstream heat exchange portion being positioned to receive the combustion products for direct contact with an inner surface of said at least one substantially vertical flue tube adjacent said upper surface of said water tank and along an entire length of said at least one substantially vertical flue tube between said upper surface and said bottom surface of said water tank, each of said vertical flue tubes having a wall positioned for contact with water stored in the interior of the water tank; an upstream collector positioned to direct combustion products from said first pass of said flue system toward said second pass of said flue system, said upstream collector being positioned against said bottom surface of said water tank and having a surface positioned to seal against said bottom surface of said water tank; a downstream collector positioned to direct combustion products from said second pass of said flue system toward said third pass of said flue system, said downstream collector being positioned against said upper surface of said water tank; and an exhaust collector assembly positioned adjacent to said upstream collector and having a surface positioned to seal against said bottom surface of said water tank, said exhaust collector assembly being positioned to receive the combustion products from said third pass of said flue system, wherein said upstream heat exchange portion of said flue system provides primary heat exchange with water in said water tank, said downstream heat exchange portion of said flue system provides secondary heat exchange with water in said water tank, and said upstream heat exchange portion is configured to transfer more heat to water in said water tank than said downstream heat exchange portion.