An apparatus (1) includes a housing (2), an air feed duct (21) a volute (5), an impeller (4), and a motor (3) for driving the rotation of the impeller (4) so as to generate a centrifugal air flow in the volute (5). The housing (2) has a first part (18a) where wall is intended, after assembly, to extend around the motor (3), espousing the shape of this motor (3) in such a way as to lie at a substantially constant distance from this motor (3); and a second part (18b, 19) where wall is intended, after assembly, to extend around the volute (5), espousing the shape of this volute (5) so as to lie at a substantially constant distance from this volute (5). The housing (2) internally forms a salient axial lump (20) which, after assembly, sits close to the hub (10) of the impeller (4).