Abstract: A roof ventilator with a motor driven radial impeller (1) preferably having a vertical axis (15). It further comprises a housing for the impeller (1) which is connectable to the roof (20) or to a suitable wall of the room to be ventilated. On the side adjacent to the roof (20) or the wall, there is an inlet (5) extending in the direction of the impeller axis (15). The housing, which is designed as a flow housing, further comprises an outlet consisting of two outlet ports (16, 17) which are located on opposite first side walls (12, 13) of the housing. These side walls (12, 13) may be completely or almost completely open. This outlet design has the effect of diverting the medium flow away from the surroundings of the drive motor.