Abstract: An impeller for a fan comprising a hub for rotation by a drive rotor and a plurality of fan blades for rotation with the hub, the impeller further comprising a support or guide member supporting or connecting fan blades of said plurality, and wherein one or more pockets are provided in said support or guide member and open axially of the fan for receiving balance weights.

Abstract: A fan assembly for the cooling of electronic systems, where a square housing is provided with a central electric motor for the impeller, and a first main inlet surface of the housing is arranged perpendicular to the axis of rotation of the impeller and in parallel to the inflow direction, and where the flow through the fan is deflected by 90.degree. after it leaves the impeller to exit, the housing at at least one lateral outlet surface that is perpendicular to the first main inlet surface which assembly results in a drastic reduction of noise.