Extractor fan size

[Chris Hogg]

We have a small shower room and an adjacent toilet, that I intend knocking together to make into a single wet room. At present, each room has a small extractor fan with about 2 m of ducting to the outside, as neither has a window, and I intend to do away with one of the extractor fans. But will that mean I have to increase the size of the remaining fan? Is there a Building Regulation that relates extractor fan size to room volume? The current fans are 10 cm diameter, and the volume of the two rooms combined will be about 8.5 cu. m.

[TheOldFellow]

Dunno if there's a reg, but I have a similar plan and am thinking of one of these heat recovery units. Expensive, but as part of a reno project not too bad. The next pages have the standard fans.

are a good supplier, IMHO.

R.

[David Hansen]

On Fri, 24 Oct 2008 09:33:18 +0100 someone who may be Chris Hogg wrote this:-

They specify air-change rates. What matters is not the size of the fan but how many air changes it will produce in a given room when connected to ductwork of a given resistance (length, material, bends and terminal all add to the resistance).

You can doubtless look the regulations up as easily as I could, remember to get the right country as they sometimes vary.

Hint - the larger fan manufacturers tend to summarise the regulations and this can be easier to access, but if you are outwith England make sure you have the right information as they tend to reflect English regulations.

[Calvin]

responses they'll get on uk.d-i-y is perfectly capable of reading and understanding the regs. They really aren't difficult and doing so removes all of the angst. At least you will know which rules you are breaking and why! Google for odpm (office of the deputy prime minister) and building regs and follow a few links.

If what you want is opinion then you are better off here of course. Mine is that the regs demand the bare minimum and IIWY I'd fit a more capable fan than they require especially if you are only just within what's permitted. I wish I had and I'll do something about it when I next have to service the fan anyway.

[Martin Bonner]

In terms of ventilation, air-change rates are obviously the correct measurement. Moving the air at 2m/s through a 10cm diameter hole will ventilate just as effectively as moving at 1 m/s through a 14cm diameter hole - but the latter will be a LOT quieter. The OP should consider how quiet he wants the fan - big and slow is much better than small and fast.

[meow2222]

Yes, big difference. Also bigger fans at slower speeds last longer if all other things are equal.

Unfortunately bigger ductwork can be an issue, and fan price rises fast as size goes up.

NT

[The Medway Handyman]

Martin Bonner wrote: - big and slow is much better than small and fast.

As the actress said to the Bishop :-)

[TheScullster]

"Chris Hogg" wrote

Chris

If you do replace 2 with 1, whatever you do fit a quality unit! Don't go cheap shed tat with the awful concertina style duct. Try and get a Vent Axia fan calculator brochure. This tells you all you need to know about fan sizing and ducting. Fit smooth bore duct to keep airflow efficiency up and noise down (again VA calculator shows why). As others have said, larger fan running slow is far preferable. I have fitted a Vent Axia in line duct fan for main bathroom and Xpelair wall mounted unit for WC - both vastly superior to shed stuff. The Xpelair came with a 3 year guarantee IIRC and they would send someone to replace the unit! This quality comes at a price of course, but do you really want to be replacing cheap fan after cheap fan every two years?

Phil

[meow2222]

Another option is to use a 4" tangential fan, and if it isnt quiet enough add noise reduction

[Chris Hogg]

Thanks for the replies. I've looked at the Vent-Axia and Xpelair web sites and got all the information I need including the Vent-Axia calculator.