A method for operating a calorimeter and a calorimeter that is operable to perform the method, wherein the calorimeter has a reactor (1) for receiving a reaction medium, a reactor jacket (2), an in-reactor heater (4) controlled by means of a first controller (6), an outer temperature control unit (9) in thermal contact with the reactor and controlled by a second controller (10), and a measurement sensor (5) arranged in the reactor for determining a reactor temperature (Tr). The reactor temperature is controlled by the heat which is delivered to the reactor by the in-reactor heater and by the heat that is carried in and/or out by the outer temperature control unit. A dynamic control of the heating power of the in-reactor heater and of the outer temperature control unit is used to eliminate any deviation of the reactor temperature from a reactor set-point temperature.