Patent ID: 7032543

Claim:
A water heater comprising: a water tank adapted to contain water to be heated; a flue extending through the water tank and having an inlet end and an outlet end; a combustion chamber in communication with the inlet end of the flue; a plenum upstream of and in fluid communication with the combustion chamber and having an air inlet, wherein the space defined by the combustion chamber and plenum is substantially air-tightly sealed except for the air inlet and the inlet end of the flue; at least one fan sealed with respect to the air inlet such that substantially all air entering the plenum through the air inlet flows through the at least one fan, wherein operation of the at least one fan raises the pressure in the plenum and combustion chamber above atmospheric pressure; a flame arrester sealed between the plenum and combustion chamber such that substantially all air flowing into the combustion chamber from the plenum flows through the flame arrester, the flame arrester permitting ingress of flammable vapors into the combustion chamber but substantially preventing egress of flame out of the combustion chamber into the plenum; and a main burner within the combustion chamber and operable to combust a mixture of air and fuel to create hot products of combustion; wherein the hot products of combustion flow out of the combustion chamber into the inlet end of the flue, heat the water in the tank through the flue, and exit the water heater through the outlet end of the flue; wherein primary air is mixed with fuel prior to combustion at the main burner; wherein secondary air within the combustion chamber combines with the primary air and fuel mixture to complete the combustion process at an outlet of the burner; and wherein the at least one fan pressurizes both primary and secondary air in the combustion chamber.