Abstract: The invention relates to a fan unit comprising a tubular external housing which has inlet and outlet connectors placed coaxially one behind in the other. A radial impeller have backwardly directed vanes. A distributor surrounds the radial impeller and positioned downstream thereof. The distributor is secured on an inner side of the housing and having a plurality of guide vanes extending axially and circumferentially spaced around the periphery. The vanes are adapted to deflect the flow of impelled fluid radially emerging from the impeller to an axial direction and which are so inclined at an angle of attack, which is selected in accordance with the direction of emergence of the impelled fluid in relation to the axis of rotation of the radial impeller that a smooth even flow transition takes place in the distributor. The ring of guide vanes coaxially surrounds the impeller with a clearance gap of substantially constant width.