Help - Bathroom extractor fan position?

13 Jul 2005
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United Kingdom
I need to fit an extractor fan in my en-suite bathroom. The room is as per the sketch attached. Unfortunately the exterior wall is the furthest wall away from the shower so I am concerned that putting a fan through the outside wall might not extract the steam from the shower. Even if it does I imagine I will get a lot of condensed water droplets on the ceiling. In addition to this, I am not sure where I would put a vent for provide a fresh incoming air supply? in the door is probably no good as this would surely impede the flow of air from the shower.

I am now thinking it may be better to cut a vent in directly above the shower and use a duct with a decent centrifugal fan in the loft space to suck the steam directly from above the shower. Hopefully the only problem I then have is getting rid of any condensation that forms on the inside of the duct in the loft.

The duct run in the loft will be either 3m to vent out through the gable end wall or about 5m to the vent out through a soffit.

Any suggestions?
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not sure where I would put a vent for provide a fresh incoming air supply? in the door is probably no good as this would surely impede the flow of air from the shower.

Extract vent above the shower.
Another vent in the stud wall at low level next to the toilet so air is drawn in from the cupboard.

Usually the air enters under the door, but in this case that won't be any good due to the door being in the middle of the room. Make sure the door fits well, so when closed there is minimal air flow around it.
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Thanks Coljack and Flameport for your replies.

First Coljack. I have done a quick sketch of what I think I need to do in the loft but I have a couple more questions. Firstly, is my rough sketch correct? Specifically:-

1. How far should the fan be from the inlet vent above the shower (length L in my sketch).
2. I have not sloped the pipe from the vent to the fan as I am assuming I dont want condensation dripping down pipe C into the fan. Is this right?

I have stubled across reference to CONDENSATION TRAPS, should I also fit one of these? if so where is it fitted?

Next, Flamport. OK, like the idea of the vent through the studwall by the toilet pan. Do I need to put another vent into the cupboard door?

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Do I need to put another vent into the cupboard door?

Probably not - if there is a gap under/around/above the door, that will be plenty to let air into the cupboard.

A 10mm gap under a standard width door is the roughly the same as a 100mm / 4 inch diameter vent hole.
Your drawing looks fine. One thing to look at is the total duct length - some of the cheaper fans are only good to push air a max of 3metres down a 100mm duct, so check the specifications!

I look forward to a question re the electrical part of this topic :LOL:
water vapour is lighter than air so it will tend to rise towards the ceiling where you are putting the extractor (think of clouds)

also the fresh air coming under the door will be cooler so it will tend not to go out through the fan, so positioning is not a big prob for you. The room is quite small so I expect you will get plenty of air changes per hour with a decent fan.

You can flop loft insulation over the duct in the loft, this will prevent it losing heat so once it is up to the same temp as the damp air, you will not get condensation in it. But have a slight fall to the outside to take any that does form.
First thanks (again in some cases) for yet more pearls of wisdom.


Flameport, gap under the door sounds good - cheers!

Taylortwocities, thanks for the tip re the fan specs. I have used the freebie on line calculator on the TLC website. No idea if this is actually any good but maybe a good starting point. This suggests I need 145m3 per hour of suck! The fans the site suggests for this (which includes pressure loss due to ducting) are:-#

CK40F (4" size) with quoted 165m3/hr after 5m ducting
TD350 (5" size) with quoted 285m3/hr after 5m ducting
MRK100m (4" size) with quoted 140m3/hr after 5m ducting

I will be using 4 or 5 inch solid waste pipe and not the flexy stuff.

My next question is: WHICH (if any) of these fans is the one to go for? Alternatively you guys may have some suggestions for parts you are familiar with that you know to be good quality and reliable. Please let me know if you do. Further to this is would be great if you could let me know the best place to purchase the parts.

Oh yes....Lekky questions may be on their way. However, my bro is a sparks so he will be getting stiffed to advise and inspect. Basics will be adherence to zones, RCD use, cable sizing. Cable routes and protection, etc etc. In terms of the fan itself I will probably trigger this from the room light. I will be using a timed fan. Not sure if I need to go for a humidistat as well but probably not.

JohnD. Thanks. I will be wrapping insulation around the whole pipe.

Thanks again gents and I look forward to your latest feedback

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