Extractor fan in windowless bathroom

[keith6868]

My damp surveyor told me that my condensation problems in other rooms may be caused because my extractor fan is sucking air into my tiny bathroom instead of expelling it. Its an EnviroVent Silent 100 radial fan.

I have severe mildew problems, peeling paint and swelling MDF as a result.

He thought the polarity might have been inadvertently reversed but an electrician looked this morning and said everything was correct and, after trying it reversed (and some other wiring permutations) said it made no difference.

However, I have just done a test I should have done in the first place with a piece of paper which the fan sucks towards it like a vacuum cleaner so I think that diagnosis is wrong.

At any event, I have a problem and I do not know what can be the cause.

Anyone any ideas why my fan is failing to clear the moisture from the bathroom? It's 6 feet by 4.5 feet so the shower is not exactly far away from the fan.

 

[wotan]

If the fan is expelling air, then that air needs to be replaced, could you fit louvered vent panels in the bathroom door? this would then promote circulation of fresh air, and hopefully remove the condensation problem.

Wotan

 

[keith6868]

I think you are right about the circulation of air.

However, it occurs to me that the fan and the place where the air gets into this albeit tiny bathroom are actually very close together so I am wondering whether the fan is expelling the fresh air coming in and ignoring the steam from the shower.

Maybe I should be thinking of re-siting the fan so that as much of the steam as possible exists between the fan and the bathroom door.

In such a small space, that's quite difficult and, as it's a flat, a ceiling fan is not possible.

The fan is currently 2/3 of the way up the wall and only about a foot away from the door jamb. Is it possible to duct from the current position up towards the ceiling and then take a right angled turn towards the wall facing the bathroom door so that the fan ends up at the extreme top corner of the bathroom, opposite the shower?

Apart from having to move all the fitted cupboards, there's the problem of meeting regulations about how close the fan can be to the shower.

I am limited in my choice of fan - it has to be a silent model because of complaints from neighbours.

 

[^woody^]

Any ducting and bends in ducting, will reduce a fans efficiency - which could render your plan less use than what you already have. It is certainly a good idea to try and relocate the inlet, but just bear that in mind

In principle, a fan should extract as close to the main source of moisture as possible, but the main aid is that the room contains the moist air (doors closed) and that the fan draws fresh air into and across the room wherever possible - via a suitably sized air inlet.

Also check that the fan has a suitable extract rate. But that is such a small room volume, that any good 100mm fan should do. Another thing, centrifugal fans are the most efficient

Finally, there should be a 15 minute overrun on the fan, and the door should be kept shut afterwards.

And don't forget to tell your "damp specialist" or his manager that he is an idiot and does not know his job

 

[foxhole]

In a wIndowless room the fan needs to run 24/7, It consumes very little and cheaper to run than cost of redecoration.

 

[^woody^]

It does not need to run all day long. At most, a humidistat will just bring it on when needed.

 

[JohnD]

He thought the polarity might have been inadvertently reversed

I will assume that you are living in the UK, and the fan is supplied from the electricity main.

The electricity supply here is 240v AC.

AC means it is alternating current.

AC, unlike a torch battery, does not have a polarity and it is impossible to make an AC motor run backwards just by swapping the N and L conductors on their terminals.

Who is this damp idiot employed by?


Your fan is in a very strange position, they are usually fitted close to the ceiling (moisture vapour is lighter than air, and rises, hence clouds). Run it more often and longer, with the door shut, and it will suck air out. Fresh air will enter the bathroom through the gap under the door (if there isn't one, saw or plane it) assuming that the duct goes to the outside world and does not leak - verify this.

If the bathroom has an external wall you could put an extractor in a more sensible position quite easily by making a hole in the wall. Or you could buy a more powerful fan that will fit the existing duct. It is probably 110mm circular. Verify this.

Does anybody drape wet washing around your home or over radiators?

How long do you usually let the fan run after a bath or shower?

A typical bathroom extractor uses about 20W and will run for about 50 hours on 14p worth of electricity, so don't believe any tales about expense.

p.s. if you have a cheap fan and the bearings are noisy, buy a new one. You can get a ball-bearing fan for a little extra.

 

[keith6868]

Thanks for the detailed replies.

I am in the UK. I live in a ground floor flat and the bathroom has no external walls.

The outlet to the ducting can only be in the current position and is nowhere near the ceiling. Re-siting will involve extending the ducting within the bathroom itself. If the fan is placed near the ceiling, the ducting from it will have to run downwards towards the existing duct.

The neighbours had complained about the noise of my centrifugal Vent Axia fan (which did a poor job also) so I now have an axial EnviroVent Silent 100 fan instead, chosen for being silent but relatively powereful.

I run the fan whilst showering and for at least half an hour (usually more) afterwards with the door shut. There is a gap under it. There is no external wall. The duct is 1.25 metres long and runs through an adjoining lobby to the outside wall, is a solid plastic tube with no blockages and is boxed in.

My main concerns about re-siting (apart from the cost) are:

1. the direction of the additional ducting - is it ok for the duct to drop a metre to the level of the existing duct?
2. the length of the extended ducting which would be 3.7 metres in total if up to the ceiling (or 2.7 m if remaining at same level).
3. whether it is safe and legal to have the fan in the position proposed (high above the far end of the bath).
4. whether I can keep the existing fan and, if not, whether I can get one which is quiet enough not to disturb the neighbours.

 

[JohnD]

if there is room, you could put a ducted fan in the duct where it passes through the adjoining lobby. There need be no wiring inside the bathroom.

They can be more powerful, but quiet, and can be boxed in to muffle their noise even more. If you can line the mounting plate with e.g. carpet or foam rubber, and put a piece between the mounting plate and the wall, that will prevent vibration passing into the structure. A more powerful extractor like that would enable you to put a "snorkel" duct reaching near to the ceiling where there will be most water vapour. You can get a rectangular duct adaptor which will look less unsightly, It van be painted with non0drip oil-based paint. If you have room to box it in, even better.

Your existing fan seems to have an extract rate of 95 cu m/hr nominal and a noise rating of 26.5 db.

Here's an example of a ducted inline fan
http://www.screwfix.com/p/xpelair-xim100-t-in-line-bathroom-extractor-fan-timer/39675 with a timer
(also look below at the "more items" section)
It is nearly three times more powerful but only 22dBa and will give you fantastic ventilation. Some of them can be run at high or low speed.

or this one http://www.screwfix.com/p/100mm-mixed-flow-fan/26867 much cheaper but the ad shows two different noise ratings (24 and 40) so check the spec with the manufacturer

there are others at various prices, they are generally better quality than the wall-mounted ones and will last longer without getting noisy bearings. At this price you should expect the motor to have ball-bearings for silence and long life.

I am assuming you have a 4-inch duct. If you have 6-inch you can get even more powerful and quieter models.

 

[keith6868]

Thanks for the idea of having an in-line fan: I didn't know about those.

I think there could well be room for one of those within the boxing around the duct. My only concern would be vibration through the wall of the neighbours' bedroom but your idea of carpet or foam to insulate it might solve that problem.

The duct is 4 in diameter.

 

[JohnD]

you can remove the original fan (terminating the cable safely) and put the elbow on the duct for the snorkel.

The mounting plate needs to be firmly fixed to the wall, but the fan can be mounted on a separate plate or piece of ply with a piece of carpet or foam rubber between them or under the feet, to damp vibration.