Patent ID: 7337752

Claim:
Fuel-fired fluid heating apparatus comprising: an outer housing having a combustion gas outlet opening; a heat exchanger structure disposed in said outer housing and having a first flow path extending therethrough and adapted to receive and discharge a flow of fluid to be heated, and a second flow path extending therethrough, said second flow path being in thermal communication with said first flow path and adapted to receive a flow of hot combustion gas and discharge it through said combustion gas outlet opening; wall structure defining a third flow path external to said heat exchanger structure, said third flow path being interposed between and at least partially bounded by an interior surface portion of said outer housing and an exterior surface portion of said heat exchanger structure; a fuel burner operative to receive fuel and pressurized combustion air from sources thereof, combust the received fuel and combustion air, and create said flow of hot combustion gas; and blower apparatus operative to (1) discharge a first flow of air into said fuel burner as pressurized combustion air, and (2) discharge a second flow of air into said third flow path as cooling air which flows along an interior surface portion of said outer housing and mixes with and cools combustion gas being discharged from said second flow path.