A ventilation assembly has a support structure, an electric motor and a fan connected to the motor. The fan has a cup-like hub with an annular side wall and a bottom wall and which define internally a housing in which the motor extends. The hub further has a plurality of internal vanes for the ventilation of the motor, that extend from the side wall of the hub. The support structure has at least one arcuate formation which is coaxial with the axis of the fan and which extends axially inside the hub of the fan, in a partially interpenetrated relationship with the side wall of the hub to form a labyrinth-like radial path between external and internal regions with respect to the hub.