Ledjeff, K.K.LedjeffSchuler, A.A.SchulerGieshoff, J.J.Gieshoff2022-03-082022-03-081996https://publica.fraunhofer.de/handle/publica/303558A water heater has a gas inlet (8) for a combustible gas and air mixture and an inlet for a fluid to be heated (11, 18) which is partially surrounded by at least one fluid chamber (4, 7) filled with the fluid (2). The exhaust gas emerging from the combustion chamber or chambers (11, 18) flows through the exhaust heat exchanger together with the fluid (2). Thereby, there are two combustion stages, whereby the first combustion stage (16) is a catalytic splitting burner (11) and the second combustion stage (20) is a monolithic burner (18, 19). As a result of the two- stage arrangement, about 80 percent of the combustible gas is converted in the first stage (16), whereby the remaining combustible gas components are themselves converted practically without any residue at the prevailing low partial pressures in the second stage (20), in particular without NO<-x emissions.de608621697patent1992-4204320