<p>The fan (72) has several main blades (71) located about its central axis. A spiral housing (74) enclosed the fan (72) and forms an air channel (74a) through which air from the blades flows. The spiral housing has a suction opening (76), which opens out on the housing in the direction of the rotational axis. Several secondary blades (80) are located at positions corresponding to the main blades in the suction opening. The outer periphery (76a) of the suction opening is located on the outer side of the inner edge of the main blade. The main blade forms an end (71a) at the side of the suction opening, which faces the opening.</p>
