Abstract: A water heater has a tank having an upper and a lower domes which are penetrated by tubular flues in a 1-1-5 arrangement of a first flue connected to a second flue which in turn is connected to tertiary condensing flues. A gas-fired burner on the upper dome fires into the first flue. Both the first and second flue have heat exchange capacity enhanced by a multiplicity of rectangular metal fins welded in a helical arrangement. Some or all of the fins in the first flue may be stainless steel, while the remaining fins may be a different material, such as mild steel. The first and second flues are arranged to remove approximately 82-89 percent of the heat generated by the burner with minimal or no formation of condensate. Approximately 5.5-9 percent of the heat generated by combustion in the burner is removed in third flues where condensation takes place.

Abstract: A forward combustion type condensing gas water heater is provided including a burner, a primary heat exchanger, a drain pipe for condensation water, a gathering and discharge device for condensation water, a secondary heat exchanger. The gathering and discharge device and the secondary heat exchanger have center lines different from the primary heat exchanger. Flue gas rises through the primary heat exchanger and passes through the secondary heat exchanger in a direction staggered with respect to the falling direction of condensation water. The condensing gas water heater effectively avoids resistance between the condensation water and the flue gas and prevents the condensation water from flowing to the burner, the combustion chamber, and the ignition pin.