My 5 yr old bathroom ceiling extractor fan does not appear to be shifting much air - can hardly feel a draught when my hand is near it. I have cleaned out the fan and the short duct to the roof ( there was quite a bit of gunge there) and checked the outlet on the roof is clear. Do they wear and become less efficient with time? Are there more powerful 100mm fans available? Guess this was a cheap one as it was installed by a well known DIY chain.