Best way to reduce a 6inch hole to 4 inch?

[spirit]

I am replacing the extractor fane in a (very) small ensuite bathroom (1.75m x 1.45m).

After removing the current (very noisy) fan I see it has a 6 inch vent. The fan I bough to replace it has a 4 inch vent.

Rather than fill the 6 inch hole up, wait for it to dry and then drill a 4 inch hole, can anyone suggest a good way of reducing the 6 inch hole to 4 inch (and in such a way that would give something for the new fan to screw onto)

thanks

 

[John D v2.0]

My honest advice would be take the fan beck and get A 6 inch one. The air will be moving slower so it will be quieter, all other things being equal.

Failing that put the smaller duct in the bigger, fill behind with glass wool and expansion foam, cut a plywood to size with a hole for the new fan, then screw the new fan to the plywood

 

[TicTac]

Use a piece of round ducting, and fill around the edges with cement.

 

[23vc]

Or plasterboard and use the plasterboard plugs to fix new fan, easier to cut than ply and you can skim/paint it

+agree John 6inch is way more effective but all the ones I’ve ever fitted sound like jet engines

 

[John D v2.0]

jet engine is funny! uifn it's that loud it's probably shifting more than 15 l/s

 

[23vc]

Tbf probably they weren’t the silent ones but they’re pricey in 6inch

 

[spirit]

Thanks for the tips on reducing the hole from 6" to 4".

It's the noise of the 6" ones that's worrying me - one of the reasons for replacing the current one is that it sounds like a jet engine and its in the en-suite of our bedroom.

I did some research and bought a 4" fan called a "Silent Tornado" which is supposed to be the best 4" fan there is.

I do wonder if there is a six inch fan in there for a reason though... 23vc - I'm having trouble even finding any silent 6" ones - can you tell me a make/model to look at please?

The fan is on an exterior wall, so there is only 300mm of ducting to outside - the electrician said that given the run is so short, as long as the fan had a good seal against the tiles (so there was nowhere else for the air to go) then we could probably just vent it straight out of the 6" duct... any reason why we couldn't / shouldn't do that?

Thanks

 

[23vc]

From a random google, this? https://www.plumbworld.co.uk/xpelai...ekzJHkpPcmnju62UvZTvfQ3QMDAHNTH4aAqixEALw_wcB

I’ve fitted a couple of these and they seem good and very quiet https://www.extractorfanworld.co.uk...hj50xtsyevdzt5gz7x2il4ehp-yizxliaanq_ealw_wcb

Pretty sure 4 inch is a safer bet noise wise and I’d agree with electrician re short duct being ok

 

[JohnD]

a 6 inch will be quieter than a 4 inch of the same throughput.

I have used quite large fans, and none of them has been as noisy as a 4" on high.

You can find the throughput and the noise in db in the listings of good suppliers.

for example
41db, 4 inch
https://www.tlc-direct.co.uk/Products/RDG510T.html
also
https://www.tlc-direct.co.uk/Products/BGWF100T.html

25db 4 inch (more expensive)
https://www.tlc-direct.co.uk/Products/ADQT100B.html

35db 6 inch - and it has three times the power of the above
https://www.tlc-direct.co.uk/Products/ADAUE150T.html

A 2-speed one on slow will be even quieter, but I can't see one just now.