Method for determining the heating up, due to the totality of thermal losses, of an electrical rotating machine with motorised ventilation, under nominal operating conditions defined by a nominal supply frequency (F N), a nominal supply voltage (U N), a nominal supply intensity (I N) and a nominal rotation speed (N N), the machine comprising a rotor and a stator and a motorised fan equipped with a specific drive device, the motor being supplied with a given supply frequency, supply voltage and supply intensity, characterised in that it comprises three steps: a) a step of measuring a first heating value Δθ 1 of the machine when: - the rotor is immobilized relative to the stator, - the supply frequency is a first reduced frequency (F 1), - the supply voltage is a first reduced voltage (U 1), - the supply intensity is the nominal intensity (I 1 = I N), - the ventilation is in operation, b) a step of measuring a second heating value Δθ 2 of the machine when: - the rotor is turning at a reduced rotation speed without load, - the supply frequency is a second reduced frequency (F 2), - the supply voltage is a second reduced voltage (U 2), - the supply intensity is a second reduced intensity (I 2), - the ventilation is in operation, c) a step of measuring a third heating value Δθ 3 of the machine when: - the rotor is turning at the nominal rotation speed without load, - the supply frequency is the nominal frequency (F N), - the supply voltage is the nominal voltage (U N), - the supply intensity is equal to the intensity of the nominal magnetising current (I ο) of the machine, - the ventilation is in operation, d) a step of calculating, from the first, second and third heating values, the heating under nominal operating conditions by: Δ θ a = Δ θ 1 − Δ θ 2 + Δ θ 3. a) a step of measuring a first heating value Δθ 1 of the machine when: - the rotor is immobilized relative to the stator, - the supply frequency is a first reduced frequency (F 1), - the supply voltage is a first reduced voltage (U 1), - the supply intensity is the nominal intensity (I 1 = I N), - the ventilation is in operation, - the rotor is immobilized relative to the stator, - the supply frequency is a first reduced frequency (F 1), - the supply voltage is a first reduced voltage (U 1), - the supply intensity is the nominal intensity (I 1 = I N), - the ventilation is in operation, b) a step of measuring a second heating value Δθ 2 of the machine when: - the rotor is turning at a reduced rotation speed without load, - the supply frequency is a second reduced frequency (F 2), - the supply voltage is a second reduced voltage (U 2), - the supply intensity is a second reduced intensity (I 2), - the ventilation is in operation, - the rotor is turning at a reduced rotation speed without load, - the supply frequency is a second reduced frequency (F 2), - the supply voltage is a second reduced voltage (U 2), - the supply intensity is a second reduced intensity (I 2), - the ventilation is in operation, c) a step of measuring a third heating value Δθ 3 of the machine when: - the rotor is turning at the nominal rotation speed without load, - the supply frequency is the nominal frequency (F N), - the supply voltage is the nominal voltage (U N), - the supply intensity is equal to the intensity of the nominal magnetising current (I ο) of the machine, - the ventilation is in operation, - the rotor is turning at the nominal rotation speed without load, - the supply frequency is the nominal frequency (F N), - the supply voltage is the nominal voltage (U N), - the supply intensity is equal to the intensity of the nominal magnetising current (I ο) of the machine, - the ventilation is in operation, d) a step of calculating, from the first, second and third heating values, the heating under nominal operating conditions by: Δ θ a = Δ θ 1 − Δ θ 2 + Δ θ 3.