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Extractor fan reducer

hi I have removed an old extractor fan and found the connection tube is c.9cm in diameter. I haven't been able to find any extractor fans with such a small diameter, can you please let me know 1) normally should I get 100 to 90 reducer? And 2) if 90 still doesn't fit, can I get a 100 to 80? Will it work as long as the reducer fit in the hole in the wall, or does it have to fit in exactly very tightly? Many thanks in advance! My builder wanted to drill open a bigger hole on my wall which is concrete but I really hope there's a simpler solution than that. Thanks.

1 Answer from a MyBuilder Electrician

Best Answer

Hi Becky,

Most domestic fans are 100mm in diameter, if you reduce the cross sectional area available to expel the air then the fan will have to work harder than it is designed to work to get the air out of the narrower hole.
This will put extra strain on the fan and may shorten its life and also won't be as effective at removing air from the room.

If it's a concrete wall it shouldn't be too difficult for your builder to cut a larger hole with a diamond core drill. This is what I would do in this situation.

If you do try and reduce the size of the pipe then it is important to ensure the joins are tight, preferably glued and sealed with aluminium tape as you don't want any moisture laiden air getting into the concrete wall as this could cause more problems with damp than is solves.

I hope that helps.


Answered 31st Jul 2015

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