Extractor fan

[andyj941]

Hi I have what really is a small bathroom with a volume of 9.7 m3. It's got a bath and shower on a mixer tap. At the moment the amount of condensation is quite bad when we use the shower even with the 'airlow' extractor fan on. This doesn't have any info on it about how much it removes per hour but I've seen that for a shower 15-20x the volume of the room is required but this is a removal of 145 m3 per hour at least - all the 100mm fans I've looked at remove up to about 85 m3 per hour.

Basically what I'm asking is whether 85 m3 would be adequate for such a small room. The old one lets wind blow into the room until its on and then it doesn't feel like it's sucking any air out even when you put your hand right up to it. It's in the ceiling and is ducted to the vent in the roof by a couple of metres of flexible ducting. Thanks for your help!

 

[PrenticeBoyofDerry]

By calculation given 9.7m3.
You need a performance rating 17500 litres per hour or 175m3 per hour.
This would do the job
http://www.tlc-direct.co.uk/Products/XPSL150.html
Try this on-line calculator to work out what size would be needed.
ventilation calculator

 

[andyj941]

Hi thanks for the reply. By my calculations 15-20 x 9.7 = 145-194m3/hour for a shower. I was hoping to keep to a 100mm fan because I'm guessing a 150mm one would need a wider hole in the ceiling and therefore a wider duct? It also needs to have a pullcord.

 

[PrenticeBoyofDerry]

If you use the on-line calculator and put in the drop down list ceiling mounted, alternative units can be found. With 100mm duct.

 

[bernardgreen]

You also need to ensure the air removed from the bath room is replaced by air from the house otherwise the fan will be unable to move any air when the air pressure in the room drops.

A gap under the door is the easiest way to achieve air flow into the room.

 

[EFLImpudence]

Where is the fan?

It won't have the desired effect if it is, for example, near or above the fresh air supply.

 

[andyj941]

Hi I never really thought of that. It's in the middle of the room (not over the bath) about 3/4 of the way from the door to the window so it's quite close to the window. The old one is very yellowed and I guess when it's on you should be able to feel it taking some air out when running but this just isn't the case. I just think a 150mm fan might be a bit big for the room!

 

[PrenticeBoyofDerry]

Does the window open?

 

[andyj941]

Yeh it opens

 

[EFLImpudence]

I guess when it's on you should be able to feel it taking some air out when running but this just isn't the case.

You should.
Have you looked above - perhaps the ducting has collapsed or somehow blocked or just too long (although I suppose it goes to the sofit).

It would appear that to be useful it really needs repositioning over the bath.

 

[andyj941]

I've looked above - it goes through the loft space and out to a vent in the roof. The length of ducting is fairly short but was a bit compressed with loads of insulation. However inside the fan itself was filthy and filled with dust. Fair comment but I'm going to go for replacing it in the same position to avoid leaving a hole in the ceiling and having to cut a new one.

 

[JohnD]

generally, a centrifugal fan is quieter and more powerful than an axial one.

For the moment you can dry the bathroom out better by leaving the fan running longer - 20 minutes after a shower is quite usual, you can leave it running 24 hours a day if you want (people tend to turn them off either because they are noisy, or because they wrongly believe it is expensive on electricity)

You say yours is in the loft and has a duct. Make sure the duct is covered in insulation to prevent it getting cold and having condensation

Also, in this position, you can get a loft-mounted in-line extractor which can be quite powerful, and will almost certainly solve your problem. As it is not fitted in the bathroom this is not notifiable electrical work. preferably have it turned on by the lightswitch and fit a plain neat grill to the bathroom ceiling.

Here are some examples:
http://www.screwfix.com/search.do?fh_search=in-line+fan

The little weedy white ones at £25 or so are not much good. Have a look at the extract rates and the noise level in dba. You can enclose it in the loft so you don't hear it much. The bigger ones are more solidly made and will last a long time.

p.s. an electric fan in a bathroom, which is mounted directly above a bath or shower, is considered more prone to water splash, so the electrical regulations are much more stringent, and the compliant fans are either very weedy (extra-low voltage), or more expensive (waterproof).