I live in a flat which does not have a window in the bathroom. My current fan may not be strong enough to extract all of the moist air as the vent from the fan has to pass vertically through approx. 4 metres to exit through pipe on top of roof. Moisture is collecting in the duct behind the fan so I have had to disconnect it. The bathroom measures approx. 8 cubic metres. Current fan is 220-240V, 15W Max.