according to the invention the control unit 40 u2032 is provided with a first output stage 42 a for the first fan motor 14 and a second output stage 42 b for the second fan motor 24 each of the output stages having an electronic switch 44 a and 44 b respectively and a freewheeling diode 46 a and 46 b respectively which operate in the same way as described in connection with the first exemplary embodiment via the control lines 52 a and 52 b the electronic switches 44 a and 44 b can each be driven with a pulse width modulated signal by the common control unit 54 u2032 however in the second exemplary embodiment of the fan installation according to the invention the feed line 14 a and the ground line 14 b lead to the first output stage 42 a and the feed line 24 a and the ground line 24 b lead to the second output stage 42 b and are therefore driven separately from each other by the electronic switches 44 a and 44 b respectively provided for the fan motors 14 and 24 nevertheless in the second exemplary embodiment of the fan installation according to the invention the entire control unit 40 u2032 is also disposed in the first housing 12 of the first fan 10 however in this case the heat sink 70 u2032 is respectively provided with a ribbed heat sink 72 a and 72 b preferably on opposite sides of the circuit board 60 each ribbed heat sink 72.