Method for controlling a hydronic heating system, the hydronic heating system having at least two indoor units which are installed in different rooms, a thermostat being installed in each of the different rooms, wherein a temperature of a heat transport medium of the hydronic heating system is controlled based on a temperature measured by the thermostat installed in that room of the different rooms, in which the indoor unit of the at least two indoor units having the slowest responsiveness is installed, characterized in that a standard heat transport medium temperature is calculated in a first step as follows: a required heat transport medium temperature T w,i is calculated for each thermostat i as T w,i = α i T set,i − T a + T dset,i wherein α i = T dw,i − T dset,i / T dset,i − T da where T dw,i is a predefined design heat transport medium temperature of the indoor unit corresponding to thermostat i, T dset,i is a standard set room temperature, T da is a predetermined lowest ambient temperature, T set,i is a set room temperature and T a is an ambient temperature, and then in case of heating the rooms a maximum of the required heat transport medium temperatures T w,i and in case of cooling the rooms a minimum of the required heat transport medium temperatures T w,i is defined from all i as the standard heat transport medium temperature, wherein the standard heat transport medium temperature is adjusted in a later step based on a measurement by the thermostat installed in that room of the different rooms, in which the indoor unit of the at least two indoor units having the slowest responsiveness is installed, wherein the temperature of the heat transport medium is controlled to be the adjusted standard heat transport medium temperature. the hydronic heating system having at least two indoor units which are installed in different rooms, a thermostat being installed in each of the different rooms, wherein a temperature of a heat transport medium of the hydronic heating system is controlled based on a temperature measured by the thermostat installed in that room of the different rooms, in which the indoor unit of the at least two indoor units having the slowest responsiveness is installed, characterized in that a standard heat transport medium temperature is calculated in a first step as follows: a required heat transport medium temperature T w,i is calculated for each thermostat i as T w,i = α i T set,i − T a + T dset,i wherein α i = T dw,i − T dset,i / T dset,i − T da where T dw,i is a predefined design heat transport medium temperature of the indoor unit corresponding to thermostat i, T dset,i is a standard set room temperature, T da is a predetermined lowest ambient temperature, T set,i is a set room temperature and T a is an ambient temperature, and then in case of heating the rooms a maximum of the required heat transport medium temperatures T w,i and in case of cooling the rooms a minimum of the required heat transport medium temperatures T w,i is defined from all i as the standard heat transport medium temperature, wherein the standard heat transport medium temperature is adjusted in a later step based on a measurement by the thermostat installed in that room of the different rooms, in which the indoor unit of the at least two indoor units having the slowest responsiveness is installed, wherein the temperature of the heat transport medium is controlled to be the adjusted standard heat transport medium temperature. a required heat transport medium temperature T w,i is calculated for each thermostat i as T w,i = α i T set,i − T a + T dset,i wherein α i = T dw,i − T dset,i / T dset,i − T da where T dw,i is a predefined design heat transport medium temperature of the indoor unit corresponding to thermostat i, T dset,i is a standard set room temperature, T da is a predetermined lowest ambient temperature, T set,i is a set room temperature and T a is an ambient temperature, and then in case of heating the rooms a maximum of the required heat transport medium temperatures T w,i and in case of cooling the rooms a minimum of the required heat transport medium temperatures T w,i is defined from all i as the standard heat transport medium temperature, wherein the standard heat transport medium temperature is adjusted in a later step based on a measurement by the thermostat installed in that room of the different rooms, in which the indoor unit of the at least two indoor units having the slowest responsiveness is installed, wherein the temperature of the heat transport medium is controlled to be the adjusted standard heat transport medium temperature.