A bearing unit comprises a radially outer stationary race (1) and a pair of radially inner rotatable half-races (2a, 2b). An intermediate annular chamber (8) is defined between the outer race (1) and the inner half-races. The intermediate chamber communicates with the outside through first air passages (5) formed in the outer race and with the inside of the bearing unit through second radial air passages (6) defined between the inner half-races. The second passages (6) are defined by an intermediate annular member (10) which is axially interposed between the inner half-races (2a, 2b) and forms one or more blade surfaces (12a, 12b) extending from the second passage (6) to the intermediate chamber (8) for capturing air from the intermediate chamber and conveying it into the second passage.