Bathroom fans

patagonia · 11 Feb 2013

Are there any bathroom fans which remove steam and smells? Are some better than others?

When we moved to this house we noticed the fan in the bathroom ceiling (close to the cornice and outside wall) didn't seem to cope with the steam when bathing or bathroom smells so my son-in-law bought a Greenwood Airvac 4" Bathroom/toilet fan from B&Q and fitted that. I was ill at the time so didn't pay much attention but the mirrors still steamed up and the other day I noticed, after I'd left the bath water in for a while (was interrupted by a phone call), that not only the mirrors and walls but even some of the floor was wet where water had condensed on the loo cistern and dripped off. I went outside and put my hand against the grille in the wall and could feel no current of air.

How do other people cope with this problem? I spoke to Greenwood and was told that one couldn't expect it to cope with steam and smells as it was only l5 l. per second and if one wanted something more powerful one would have to install a kitchen fan. I find this hard to believe. I don't know whether the fact that the duct pipe has to bend rather acutely to get through the wall has anything to do with it. Any suggestions?

Aragorn84 · 11 Feb 2013

Essentially a 4" wall mounted fan is unlikely to flow anywhere near the amount of air required to properly remove the moisture from a bathroom.

They're often sized to meet the minimum requirements that the building regs specify and nothing more, and these requirements are unfortunately really low.

Use this calculator:

http://www.tlc-direct.co.uk/Technical/Ventilation/Ventilation4.html

To work out the flow rate you actually need, then find a suitable fan.

You may find keeping the 4" duct, but installing a loft mounted inline fan instead would meet the airflow requirements, without having to install a 6" or larger fan.

Taylortwocities · 11 Feb 2013

Don't forget. You have a 100mm dia hole in teh wall. You must allow at least that amount of air to enter the room or the fan won't be efficient.

Also, the fan needs to be at the opposite end of the room to the air inlet point.

It must be a timer fan. You'll need an over-run time of 15minutes+

SaladFingers · 11 Feb 2013

Taylortwocities said:
It must be a timer fan. You'll need an over-run time of 15minutes+

Not necessarily.

A humidistat is perfectly fine and a lot better.

Besides, if there's a window that can be opened and of adaquate size, then forced air flow isn't required by building regs, but makes your bathroom environment a lot cleaner.

I find 4" fans barely do anything, 6" fans make a big difference.

patagonia · 11 Feb 2013

So we should leave the bathroom door open then and let the smells and steam drift into the hall? The fan is immediately above the window which is one large one (no little one at the top) so I wouldn't want that open while I was in the bath in the winter. It does have a timer and seems to run a long time after switching off. Comes on whenever we switch the light on. I suppose we cd open the window and not switch the light & fan on in the summer but the bathroom is on the ground floor. Nice treat for the postman!

Why do they sell these stupid things if they are not fit for purpose? No wonder so many houses have condensation problems.

SaladFingers · 11 Feb 2013

You'll find that an interior door does not provide a perfect seal, so even a closed door will let enough air supply in underneath it. It is mentioned as such in the building regs somewhere as an acceptable means of supply to supplement forced extract.

patagonia · 11 Feb 2013

Should one be able to feel any air coming out through the exterior grille?

SaladFingers · 11 Feb 2013

patagonia said:
Should one be able to feel any air coming out through the exterior grille?

If you mean when the fan is on and you're feeling from the outside, yes.

JBR · 11 Feb 2013

I'm having exactly the same problem. The existing fan expels air through the (cavity) wall and has a 4" diameter opening.

Can anyone recommend a reliable and powerful fan as a replacement?

Taylortwocities · 11 Feb 2013

We assume that the 4" hole is sleeved and that the air isn't just pumping into the cavity?

I've seen that a few times

Aragorn84 · 12 Feb 2013

JBR said:
I'm having exactly the same problem. The existing fan expels air through the (cavity) wall and has a 4" diameter opening.

Can anyone recommend a reliable and powerful fan as a replacement?

Use the TLC calculator above to find out your requirements, then see if anyone makes a 4" fan that will flow anywhere near what you need.

In all likelyhood, unless your prepared to use a loft mounted inline fan, you'll struggle to get suitable airflow on the 4" duct.

The TLC page will recommend suitable fans too.

If your concerned about enough air getting into the bathroom to replace the extracted air, and your interior door is very close fitting, you can remove half an inch from the bottom of the door to allow fresh air to enter.

patagonia · 12 Feb 2013

patagonia wrote:
Should one be able to feel any air coming out through the exterior grille?

Saladfingers wrote:
If you mean when the fan is on and you're feeling from the outside, yes.

Well, I can't feel anything. Cd be there's a blockage or duct is squashed (must be rather an acute bend as it's in the ceiling so close to the wall) or just a useless fan as it's only l5 l. per sec. whereas the tlc guide suggests a heck of a lot more than that.

There is a 4" with timer that wd be OK for our size bathroom. However, we only have about 1/8 inch. under the door and I think a half inch gap wouldn't look too good in the hall. One can get one with a humidistat as well but presumably that wouldn't come on and deal with smells if there were no humidity.

JBR · 12 Feb 2013

Aragorn84 said:
JBR said:

I'm having exactly the same problem. The existing fan expels air through the (cavity) wall and has a 4" diameter opening.

Can anyone recommend a reliable and powerful fan as a replacement?

Click to expand...

Use the TLC calculator above to find out your requirements, then see if anyone makes a 4" fan that will flow anywhere near what you need.

In all likelyhood, unless your prepared to use a loft mounted inline fan, you'll struggle to get suitable airflow on the 4" duct.

The TLC page will recommend suitable fans too.

If your concerned about enough air getting into the bathroom to replace the extracted air, and your interior door is very close fitting, you can remove half an inch from the bottom of the door to allow fresh air to enter.

Thanks Aragorn. According to the TLC page you are right; a 4" duct is not sufficient. I'm going to have to widen the gap to at least 5" and get a bigger fan at around £60 or so.

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Bathroom fans

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