Method for determining a heat flow emanating from by a heat-conveying water/glycol mixture (H2O, GLY), wherein the water/glycol mixture (H 2 O, GLY) flows from an input position through a measuring section (MESS) filled with the water/glycol mixture (H 2 O, GLY) to an outlet position, wherein the water/glycol mixture (H 2 O, GLY) at the input position has an input temperature, in particular an inlet flow temperature, and at the outlet position has an outlet temperature that is lower owing to the heat flow emanating from by the water/glycol mixture (H 2 O, GLY), in particular a return flow temperature, wherein the method comprises the following steps: - detecting a temperature difference (ΔT) between the input and outlet temperatures (T1, T2), - measuring a volume flow of the water/glycol mixture (H 2 O, GLY) flowing between the inlet and outlet positions (EIN, AUS), - determining the mixing ratio R of the water/glycol mixture (H 2 O, GLY), comprising the following steps: - irradiating an ultrasonic signal with a transmission level along a measured distance, wherein the measured distance runs inside the measuring section (MESS), - measuring a receiving level of the ultrasonic signal at one end of the measured distance, - determining an ultrasonic attenuation (α) of the ultrasonic signal attenuated by the water/glycol mixture (H 2 O, GLY), in particular from the transmission and receiving levels of the ultrasonic signal, - measuring the fluid temperature of the water/glycol mixture (H 2 O, GLY) flowing through the measuring section (MESS), and - determining the mixing ratio R of the water/glycol mixture (H 2 O, GLY) from the determined ultrasonic attenuation (α) and from the measured fluid temperature, - determining a density (ρ) and specific heat (c p) of the heat-conveying water/glycol mixture (H 2 O, GLY) from the measured fluid temperature and from the determined mixing ratio R of the heat-conveying water/glycol mixture (H 2 O, GLY), and - determining the heat flow emanating from the water/glycol mixture (H 2 O, GLY) from the product of the measured volume flow, from the measured temperature difference (ΔT), from the determined density (ρ) and from the determined specific heat (c p). - detecting a temperature difference (ΔT) between the input and outlet temperatures (T1, T2), - measuring a volume flow of the water/glycol mixture (H 2 O, GLY) flowing between the inlet and outlet positions (EIN, AUS), - determining the mixing ratio R of the water/glycol mixture (H 2 O, GLY), comprising the following steps: - irradiating an ultrasonic signal with a transmission level along a measured distance, wherein the measured distance runs inside the measuring section (MESS), - measuring a receiving level of the ultrasonic signal at one end of the measured distance, - determining an ultrasonic attenuation (α) of the ultrasonic signal attenuated by the water/glycol mixture (H 2 O, GLY), in particular from the transmission and receiving levels of the ultrasonic signal, - measuring the fluid temperature of the water/glycol mixture (H 2 O, GLY) flowing through the measuring section (MESS), and - determining the mixing ratio R of the water/glycol mixture (H 2 O, GLY) from the determined ultrasonic attenuation (α) and from the measured fluid temperature, - irradiating an ultrasonic signal with a transmission level along a measured distance, wherein the measured distance runs inside the measuring section (MESS), - measuring a receiving level of the ultrasonic signal at one end of the measured distance, - determining an ultrasonic attenuation (α) of the ultrasonic signal attenuated by the water/glycol mixture (H 2 O, GLY), in particular from the transmission and receiving levels of the ultrasonic signal, - measuring the fluid temperature of the water/glycol mixture (H 2 O, GLY) flowing through the measuring section (MESS), and - determining the mixing ratio R of the water/glycol mixture (H 2 O, GLY) from the determined ultrasonic attenuation (α) and from the measured fluid temperature, - determining a density (ρ) and specific heat (c p) of the heat-conveying water/glycol mixture (H 2 O, GLY) from the measured fluid temperature and from the determined mixing ratio R of the heat-conveying water/glycol mixture (H 2 O, GLY), and - determining the heat flow emanating from the water/glycol mixture (H 2 O, GLY) from the product of the measured volume flow, from the measured temperature difference (ΔT), from the determined density (ρ) and from the determined specific heat (c p).