Heat management method of a - high-temperature steam electrolysis [SOEC] (Fig. 1), - solid oxide fuel cell [SOFC] (Fig. 2) having high-temperature steam electrolysis [SOEC] (Fig. 1) and/or - reversible high-temperature fuel cell having SOEC and SOFC modes [rSOC] (Fig. 1/2), wherein required steam is supplied from at least one external source and at least one exhaust gas stream (4, 12, 12a) downstream of the cell [SOEC, SOFC, rSOC] (5, 5a) is cooled (3, 11, 18, 35) at least once, wherein required steam (1, 8) is generated internally by the internal recuperative heating of externally supplied water (47, 48, 51), wherein the energy from the at least one cooling (3, 11, 18, 35) of the at least one exhaust gas stream (4, 4a, 12, 12a, 17, 20, 34, 36) to be cooled is used for this purpose, and in the process the external steam supply (1, 38) is reduced or switched off, characterised in that heat sources at temperatures of less than 100°C are used for the internal steam production (1, 57), wherein either a) - water is evaporated at low pressures of less than 1 bar, wherein - the pressure of the produced steam is subsequently increased to the operating pressure of the electrolysis or - electrolysis is carried out at low pressures, wherein the electrolysis products (61, 62) formed, at least hydrogen, are conveyed to a pressure increase (59, 60) prior to further processing; or b) by means of a heat pumping process, the temperature level of the heat sources is raised to a level that is useful for the steam generation for the electrolysis; or c) an internal recirculation of the products downstream of the cell, in particular the hydrogen (2, 4, 87), is used as a carrier gas for steam production. - high-temperature steam electrolysis [SOEC] (Fig. 1), - solid oxide fuel cell [SOFC] (Fig. 2) having high-temperature steam electrolysis [SOEC] (Fig. 1) and/or - reversible high-temperature fuel cell having SOEC and SOFC modes [rSOC] (Fig. 1/2), wherein required steam is supplied from at least one external source and at least one exhaust gas stream (4, 12, 12a) downstream of the cell [SOEC, SOFC, rSOC] (5, 5a) is cooled (3, 11, 18, 35) at least once, a) - water is evaporated at low pressures of less than 1 bar, wherein - the pressure of the produced steam is subsequently increased to the operating pressure of the electrolysis or - electrolysis is carried out at low pressures, wherein the electrolysis products (61, 62) formed, at least hydrogen, are conveyed to a pressure increase (59, 60) prior to further processing; or - water is evaporated at low pressures of less than 1 bar, wherein - the pressure of the produced steam is subsequently increased to the operating pressure of the electrolysis or - electrolysis is carried out at low pressures, wherein the electrolysis products (61, 62) formed, at least hydrogen, are conveyed to a pressure increase (59, 60) prior to further processing; b) by means of a heat pumping process, the temperature level of the heat sources is raised to a level that is useful for the steam generation for the electrolysis; or c) an internal recirculation of the products downstream of the cell, in particular the hydrogen (2, 4, 87), is used as a carrier gas for steam production.