An electric ventilator (1) comprises a frame (2), a pair of centrifugal fans (3) mounted on the frame (2), an electric motor (4) for driving the fans (3) and axially interposed between the fans (3), and a unit (5) for controlling the speed of the motor (4); the speed control unit (5) comprises a plurality of electrical switching resistors (7) housed in a box-shaped container (8) that can be closed and sealed; the container (8) is mounted on the frame (2) and has the shape of a bridge so as to surround the casing (13) of the motor (4) without touching it.