Patent ID: 8807093

Claim:
A water heater comprising: a water tank having a lower dome and an upper dome, and a tank wall extending therebetween; a first flue defining a first flue wall, the first flue extending between the upper dome and the lower dome, the first flue joining the upper dome to define an opening through the upper dome, and joining the lower dome to define an opening through the lower dome, the first flue having an inner surface to which a first multiplicity of radially inwardly extending metal fins are attached by a weld, without extending through the first flue wall; a burner mounted to the first flue so as to fire along the first flue; a controller connected to the burner to vary the BTU output of the burner; a second flue defining a second flue wall, the second flue extending along a length between the upper dome and the lower dome and spaced from the first flue, the second flue joining the upper dome to define an opening through the upper dome, and joining the lower dome to define an opening through the lower dome, the second flue having an inner surface to which a second multiplicity of radially inwardly extending metal fins are attached by a weld, without extending through the second flue wall; a first thermal junction box mounted to one of the upper dome or the lower dome and forming a passageway between the first flue and the second flue, the first junction box opposite the burner so that flue gases pass through the first flue and then pass through the second flue; and wherein the multiplicity of metal fins in the first flue begin at a location spaced downstream from the burner such that the multiplicity of metal fins are exposed to lower temperature, and the multiplicity of metal fins in the first flue extend along the first flue inner surface to the first thermal junction box, and wherein the second multiplicity of metal fins extend along the second flue inner surface.