Method P for using heat available at a temperature of less than 170°C originating from a method PH2 for producing hydrogen by steam reforming of light hydrocarbons to contribute to heating the water of a district heating water network, wherein: - the method PH2 includes at least the following steps: -- h1) generation of a syngas by steam reforming with the combined production of fumes, followed by a first cooling of the syngas by heat exchange, then conversion of the CO contained in the syngas, and a second cooling operation by heat exchange to reach a temperature TG at most equal to 160°C, -- h2) cooling of the fumes produced by successive heat exchanges with different fluids used in the method to reach a temperature TF at most equal to 170°C, -- h3) production of unavoidable export steam to feed an external steam network using demineralised water by heat exchanges with the syngas and optionally with the fumes, at a temperature TV greater than 200°C, - the method P for using heat being characterised in that it includes at least the following steps: -- a) provision of a district heating water network wherein water circulates at a variable temperature of between Tt warm water temperature, at least equal to 50°C and Tc hot water temperature, at most equal to 180°C, -- b) provision of heat transfer fluid at a variable temperature of between Tmin greater than Tt and Tmax greater than Tc circulating in a closed loop, -- c) heating of all or part of the heat transfer fluid by indirect heat exchange with the syngas after the second cooling operation at the temperature TG in step h1), -- d) heating of all or part of the heat transfer fluid by heat exchange with the steam removed from the export steam produced in step h3) at the temperature TV so as to provide a heat transfer fluid at the temperature Tmax, -- e) transfer of heat from the heat transfer fluid at the temperature Tmax to the district heating water network by indirect heat exchange with the water of said network at the temperature Tt via a substation heat exchanger so as to heat the water of the network to the temperature Tc. - the method PH2 includes at least the following steps: -- h1) generation of a syngas by steam reforming with the combined production of fumes, followed by a first cooling of the syngas by heat exchange, then conversion of the CO contained in the syngas, and a second cooling operation by heat exchange to reach a temperature TG at most equal to 160°C, -- h2) cooling of the fumes produced by successive heat exchanges with different fluids used in the method to reach a temperature TF at most equal to 170°C, -- h3) production of unavoidable export steam to feed an external steam network using demineralised water by heat exchanges with the syngas and optionally with the fumes, at a temperature TV greater than 200°C, -- h1) generation of a syngas by steam reforming with the combined production of fumes, followed by a first cooling of the syngas by heat exchange, then conversion of the CO contained in the syngas, and a second cooling operation by heat exchange to reach a temperature TG at most equal to 160°C, -- h2) cooling of the fumes produced by successive heat exchanges with different fluids used in the method to reach a temperature TF at most equal to 170°C, -- h3) production of unavoidable export steam to feed an external steam network using demineralised water by heat exchanges with the syngas and optionally with the fumes, at a temperature TV greater than 200°C, - the method P for using heat being characterised in that it includes at least the following steps: -- a) provision of a district heating water network wherein water circulates at a variable temperature of between Tt warm water temperature, at least equal to 50°C and Tc hot water temperature, at most equal to 180°C, -- b) provision of heat transfer fluid at a variable temperature of between Tmin greater than Tt and Tmax greater than Tc circulating in a closed loop, -- c) heating of all or part of the heat transfer fluid by indirect heat exchange with the syngas after the second cooling operation at the temperature TG in step h1), -- d) heating of all or part of the heat transfer fluid by heat exchange with the steam removed from the export steam produced in step h3) at the temperature TV so as to provide a heat transfer fluid at the temperature Tmax, -- e) transfer of heat from the heat transfer fluid at the temperature Tmax to the district heating water network by indirect heat exchange with the water of said network at the temperature Tt via a substation heat exchanger so as to heat the water of the network to the temperature Tc. -- a) provision of a district heating water network wherein water circulates at a variable temperature of between Tt warm water temperature, at least equal to 50°C and Tc hot water temperature, at most equal to 180°C, -- b) provision of heat transfer fluid at a variable temperature of between Tmin greater than Tt and Tmax greater than Tc circulating in a closed loop, -- c) heating of all or part of the heat transfer fluid by indirect heat exchange with the syngas after the second cooling operation at the temperature TG in step h1), -- d) heating of all or part of the heat transfer fluid by heat exchange with the steam removed from the export steam produced in step h3) at the temperature TV so as to provide a heat transfer fluid at the temperature Tmax, -- e) transfer of heat from the heat transfer fluid at the temperature Tmax to the district heating water network by indirect heat exchange with the water of said network at the temperature Tt via a substation heat exchanger so as to heat the water of the network to the temperature Tc.