Abstract: A corrugated indirect heating coil is disclosed. The heating coil includes an intake and an exhaust. Tubing connects the intake and exhaust together in fluid communication. The tubing includes a plurality of corrugations formed thereon to maximize surface area for heat exchange. The tubing is preferably wound into coils and supported by a frame.

Abstract: A fuel-fired water heater has a single pass condensing-type heat exchanger disposed within its water storage tank portion. The heat exchanger includes a primary non-condensing portion defined by a combustion chamber positioned in an upper interior portion of the tank and having a spaced series of vertical tubes depending therefrom. A secondary condensing portion of the heat exchanger is defined by a plenum having a top side connected to the bottom ends of the vertical tubes, and a bottom side from which a downwardly coiled flue tube depends. A fuel burner generates hot combustion gases that are sequentially flowed into the combustion chamber and then downwardly through the balance of the heat exchanger in a single pass.

Abstract: A fuel-fired commercial water heater has upper and lower communicated tank portions which are separated by a plenum forming a vertically intermediate portion of a dual pass condensing type heat exchanger. A lower portion of the heat exchanger is defined by a series of vertical flue tubes extending through the lower tank and intercommunicating the plenum with a combustion chamber disposed beneath the lower tank and having a fuel burner with a discharge portion communicated therewith. An upper portion of the heat exchanger is defined by a vertical flue pipe, disposed in the upper tank, that extends upwardly from the plenum and then coils downwardly around itself and horizontally exits the upper tank. During firing of water heater the burner flows flue gases sequentially through the lower tank flue tubes, the plenum, and the upper tank coiled flue pipe structure.