Bathroom extractor suggestions...

[rarara]

I am looking to fit an extractor to a 2mx3m bathroom, approx 3.5m high. I have the option of venting straight out the wall (pretty thick - maybe about 900mm in total) or just going into the attic space and joining onto one of the existing tile vents (maybe approx 3 metres or so in total).

What would be the best extractor option? And type of fan?

I happened to be in Screwfix and they has a fan by one of the common brands (Vent-Axia or so, bout £40) as a counter display and the idea was you could press a button and see how silent the thing was up close. What I did notice is that when I lifted the thing to horizontal (it claimed to be wall or ceiling mounted ) the flaps to prevent back drafts couldn't even open due to the puny flow. Obviously something like that is what I am hoping to avoid.

I suppose the criteria is powerful enough, quiet, economical and something that will be airtight/have no back drafts when not in use.

 

[OwainDIYer]

I would go through the wall wherever possible.

I prefer Vent-Axia or Xpelair rather than cheaper brands.

If you want to fit it yourself, this
http://www.screwfix.com/p/titan-tct-core-drill-kit-10-pieces/67894
looks suspiciously like Friday's deal of the day


http://www.screwfix.com/jsp/landing.jsp?id=DealoftheDay

 

[ericmark]

The first question is why do you want a fan? For 100's of years the drafts under doors and the air going up the flue allowed enough exchanges of air.

If like many you have sealed up all places where drafts can get into the house then pumping air out just will not work.

In the main it takes time for any moisture to transfer into the air of the room and for a fan to run for 5 minutes is a waste of time.

For some reason we all seem to think we can blow air out and my magic it is replaced. My wife will run the tumble dryer then state "There is a terrific draft from under that door. Switch the tumble dryer off and the draft vanishes.

The cure is a heat recovery unit but these are expensive. The chimney effect is surprising and once started really hard to stop. So from a warm room straight up and you will not need a fan. Having flaps where you have an open plan house is useless once the draft is started you will never stop it without some mechanical means to hold them closed.

It would seem some one in government decided we should have fans in a bathroom where the window does not open which is fair enough but when it will open leaving window open for 1/2 hour is far better than any fan.

 

[JohnW2]

It would seem some one in government decided we should have fans in a bathroom where the window does not open which is fair enough ....

Well, it would be fair enough if they had some way (which they obviously don't) of compelling people to open an openable window if they have one.

... but when it will open leaving window open for 1/2 hour is far better than any fan.

In practice, people who have openable bathroom windows seem to rarely open them. They usually leave the window closed and either moan about the condensation or install and use an (often inadequate) extractor. What I don't really understand is that if one does open the window when it's cold outside (and hot/moist inside), the tendency often is for the cold air to 'rush in' and cool the room, often causing the water vapour in the bathroom air to condense.

Kind Regards, John

 

[EFLImpudence]

What I don't really understand is that if one does open the window when it's cold outside (and hot/moist inside), the tendency often is for the cold air to 'rush in' and cool the room,

Only if it is 'rushing out' elsewhere in the house.
The flow may be in the other direction.

often causing the water vapour in the bathroom air to condense.

Do you mean it would rain?
If there were no draughts past the bathroom door then the only cold air that can come in would be that replacing the higher hot/moist air which has escaped.

 

[JohnW2]

What I don't really understand is that if one does open the window when it's cold outside (and hot/moist inside), the tendency often is for the cold air to 'rush in' and cool the room,

Only if it is 'rushing out' elsewhere in the house. The flow may be in the other direction.

Indeed - but although I don't fully understand, my experience is that the cold air often 'rushes in'. I suppose that it could be that warm moist air 'rushes out' of the top of the open window, to be replaced by cold air 'rushing in' through the lower part of the open window (hence maybe fairly obvious to an occupant).

often causing the water vapour in the bathroom air to condense.

Do you mean it would rain?

Essentially yes.

If there were no draughts past the bathroom door then the only cold air that can come in would be that replacing the higher hot/moist air which has escaped.

Indeed - see above. However, there are two things going on. Escaping warm/moist air will gradually be replaced by cold air from outside, (maybe both through the same window), but the entering cold air will also cool the warm/moist air which hasn't yet left the room, hence potentially leading to 'rain' (or, at least, visible 'cloud'/'steam' formation).

Kind Regards, John

 

[JohnD]

If you don't have an extractor, the steam and water vapour will drift about until they either condense, or find their own way out. Most likely you have modern windows which are not draughty like old sashes used to be, and you probably do not have open fireplaces in all rooms sucking warm air up the chimney.

An extractor in a bathroom creates suction which prevents the water vapour diffusing through your home. It works best with the door and window shut. cool dry air from the house enters to replace it though the gap under the door, and stratifies under the warm wet air which rises towards the ceiling and is sucked out. The stratification also works much better with door and windows shut as it reduces mixing of the wet and the dry air. Water vapour is lighter than air, hence clouds.

if you have room above the ceiling, you can fit an inline ducted fan, which can be quieter, and about three times as powerful, as a typical wall fan.

 

[JohnW2]

If you don't have an extractor, the steam and water vapour will drift about until they either condense, or find their own way out. Most likely you have modern windows which are not draughty like old sashes used to be, and you probably do not have open fireplaces in all rooms sucking warm air up the chimney.

Is that directed at me (quotes sometimes help )? If so, in my house you won't find any modern windows, but you will find plenty of draughty ones, and plenty of open fireplaces, many with very tall chimneys!

Kind Regards, John

 

[EFLImpudence]

If there were no draughts past the bathroom door then the only cold air that can come in would be that replacing the higher hot/moist air which has escaped.

Indeed - see above. However, there are two things going on. Escaping warm/moist air will gradually be replaced by cold air from outside, (maybe both through the same window), but the entering cold air will also cool the warm/moist air which hasn't yet left the room, hence potentially leading to 'rain' (or, at least, visible 'cloud'/'steam' formation).

The cold air coming in will not quickly mix with the warm air; it will sink forcing the warm air up.

I think your 'rush' is confusing; is it not just the reduction in temperature?
Without draughts past the door or wind outside, the volume of cold air entering is limited to that of the warm air leaving.
If the cold air is drier then the result is reduced moisture in the bathroom.

It depends on the shape and style of the window and the currents formed.

 

[JohnW2]

The cold air coming in will not quickly mix with the warm air; it will sink forcing the warm air up.

Sure, but that cold air coming/'rushing'in through the lower part of the window opening will often be at just about the right height to hit an occupant as it 'enters and sinks'.

I think your 'rush' is confusing; is it not just the reduction in temperature?

Indeed - but that reduction in temperature is due to the 'rush' ('inflow' if you prefer!) of colder air, isn't it.

Without draughts past the door or wind outside, the volume of cold air entering is limited to that of the warm air leaving. If the cold air is drier then the result is reduced moisture in the bathroom.

Indeed - but that doesn't mean that the reduction in temperature cannot result in condensation of water vapour within the room, even if the overall/average moisture level has been reduced by exchange of some warm/moist and cold/dry air, does it?

It depends on the shape and style of the window and the currents formed.

Indeed - that is the crucial factor.

Kind Regards, John

 

[EFLImpudence]

Indeed - but that doesn't mean that the reduction in temperature cannot result in condensation of water vapour within the room, even if the overall/average moisture level has been reduced by exchange of some warm/moist and cold/dry air, does it?

Mmm. You are probably correct at the meeting of cold and warm air but people do not complain of increased visible water vapour and I do not believe that this will result in increased condensation on the walls or ceiling because, as you say, the overall humidity will be reduced.

If the window was closed when half of the warm moist air had been replaced then their would be less humidity than if the window had not been opened.


As you have said, your house has plenty of ventilation and you do not suffer with the problem.

It is the same as my suggestion of leaving a sopping cloth in the car. In the morning the inside of the windows would be covered in condensation.
You would, probably without thinking about it, open the windows and turn on the fan which blows air in and out of the windows to get rid of it.

 

[Grenage]

I installed a Ventaxia ACM100T, which is an in-line fan for ceilings; it's been an excellent addition.

 

[EFLImpudence]

I installed a Ventaxia ACM100T, which is an in-line fan for ceilings; it's been an excellent addition.

Did you have a problem with mould before?

 

[JohnW2]

Indeed - but that doesn't mean that the reduction in temperature cannot result in condensation of water vapour within the room, even if the overall/average moisture level has been reduced by exchange of some warm/moist and cold/dry air, does it?

Mmm. You are probably correct at the meeting of cold and warm air but people do not complain of increased visible water vapour and I do not believe that this will result in increased condensation on the walls or ceiling because, as you say, the overall humidity will be reduced. ... If the window was closed when half of the warm moist air had been replaced then their would be less humidity than if the window had not been opened.

I'd have to do some sums to be sure, but I'm far from convinced that what you say is necessarily correct. Words like 'moisture' and 'humidity' are being used in rather loose ways. What determines whether condensation will occur is the relationship between temperature and water content of the air. If the total water content of the air in the room is reduced AND the temperature of the air is also reduced, then whether or not condensation results will depend upon the relative degrees of reduction in water content and reduction in temperature.

As you have said, your house has plenty of ventilation and you do not suffer with the problem.

That's not actually the case. Although my house is fairly draughty, a lot of it is also cold. Condensation in bathrooms (and sometimes other rooms!) on walls, ceilings, mirrors, shower cubicle walls etc. is therefore quite common. As above, temperatures are as important as air water content. However, despite the condensation, we've almost never had any mould problems - which is why I previously said that I don't really understand why 'mould experiences' seem to differ so much between properties.

It is the same as my suggestion of leaving a sopping cloth in the car. In the morning the inside of the windows would be covered in condensation. .... You would, probably without thinking about it, open the windows and turn on the fan which blows air in and out of the windows to get rid of it.

Once one has the condensation, all one can do is to do things to cause it to evaporate, and raising the temperature (hence dew point) is the best way. When one tries to get rid of it, disappearance of the condensation is usually very slow until the the air being blown by the car's heater/fan gets hot - it would take a long time if one tried to do it simply by replacing the air within the car with cold, but dryer, air - try demisting your windscreen with the 'heater' set to 'cold'!

Kind Regards, John

 

[EFLImpudence]

I'd have to do some sums to be sure, but I'm far from convinced that what you say is necessarily correct. Words like 'moisture' and 'humidity' are being used in rather loose ways. What determines whether condensation will occur is the relationship between temperature and water content of the air. If the total water content of the air in the room is reduced AND the temperature of the air is also reduced, then whether or not condensation results will depend upon the relative degrees of reduction in water content and reduction in temperature.

Yes, it will but you may be getting too technical for a person complaining of mouldy bathrooms.
As the air in a bathroom will be 'steamy' (full of visible water vapour) and the air coming in will not be then I think the result is going to be as I have thought.

That's not actually the case. Although my house is fairly draughty, a lot of it is also cold. Condensation in bathrooms (and sometimes other rooms!) on walls, ceilings, mirrors, shower cubicle walls etc. is therefore quite common.

Well, it will be; that is inevitable.
However, what happens after that is the determining factor.

As above, temperatures are as important as air water content. However, despite the condensation, we've almost never had any mould problems - which is why I previously said that I don't really understand why 'mould experiences' seem to differ so much between properties.

You have said it is quite draughty and you have chimneys.

Once one has the condensation, all one can do is to do things to cause it to evaporate, and raising the temperature (hence dew point) is the best way. When one tries to get rid of it, disappearance of the condensation is usually very slow until the the air being blown by the car's heater/fan gets hot - it would take a long time if one tried to do it simply by replacing the air within the car with cold, but dryer, air - try demisting your windscreen with the 'heater' set to 'cold'!

It depends how long you wait. You probably would find half an hour sat waiting unacceptable but in a bathroom it would be fine.
Conversely, are you saying that a fan alone is useless?
Would this, if so, apply to extractor fans?

In my bathroom, after a bath, the tiled walls are covered in condensation - not running with - and half an hour later it is gone without opening the window or having a fan.

Mould appears where the surface never dries.
I maintain that the problems occur where the rest of the property is also, and always, humid - caused by the inhabitants - because of things like lots of plants, lots of washing and cooking, even many people, the bathroom may have been wiped and the cloth containing the water just left there..

I have been to properties I look after where the tenant has complained of mould and when you walk in it feels like the tropical house at the zoo.
Once the bath was left full of water, I do not know why it was not drained - didn't bother to ask.

None of the properties has a problem when empty.


Obviously, some places have other issues with actual leaks entering.


Also, perhaps some people worry about 'your and my type of condensation' because they think none should occur and they should be able to see in the mirror when they get out of the bath when, in fact, it is not a problem at all - it is just what happens.

It's like dust; if you don't remove it, it will just increase.