Abstract: An apparatus for heating water having three vertically aligned water heating process sections. The upper section includes an annular water storage tank disposed around a combustion chamber having a downward firing burner. The intermediate section, disposed vertically below the upper section receives flue gas from the combustion chamber, which flue gas is cooled and dehumidified, producing a hot condensate which collects in a passive condensate flow control device disposed proximate the bottom of the intermediate section. The lower section, disposed vertically below the intermediate and separated therefrom by the passive condensate flow control device receives hot condensate from the flow control device, which is used to preheat and humidify air, such as room air, which is then recycled to the combustion process of the upper section for use as combustion air.

Abstract: An apparatus for heating water having three vertically aligned water heating process sections. The upper section includes an annular water storage tank disposed around a combustion chamber having a downward firing burner. The intermediate section, disposed vertically below the upper section receives flue gas from the combustion chamber, which flue gas is cooled and dehumidified, producing a hot condensate which collects in a passive condensate flow control device disposed proximate the bottom of the intermediate section. The lower section, disposed vertically below the intermediate and separated therefrom by the passive condensate flow control device receives hot condensate from the flow control device, which is used to preheat and humidify air, such as room air, which is then recycled to the combustion process of the upper section for use as combustion air.