This apparatus (1) includes a fan (2) constituted by a motor (5), an impeller (6) and a fan scroll (7), the motor (5) being contained in a motor casing (8) having a first end connected to the fan scroll (7) and an opposite second end； and a casing (22) receiving the fan (2), defining around that fan (2) a space (23) for flow of gas for cooling the fan (2) having an inlet (24). According to the invention the first end of the casing (8) includes at least one first hole (10)； and the second end of the casing (8) includes at least one second hole (11) separated from the inlet (24) in such a manner as to prevent capture of the hot cooling gas leaving the casing (8) by the inlet (24).
