new bathroom extractor fan doesn't stop condensation

[penandink]

Really interested in this thread. Posted earlier about a similar problem we have on the decorator's forum because the amount of condensation has actually led to paper peeling off the ceiling. In Winter icicles actually form on the ceiling (masses of loft insulation up there) and bubbles now on the paper as it has dried out. Got good advice about addressing the decorating problem, but loath to redecorate without trying to fix the condensation problem first. Tested our very old fan and it is actually better and more efficient than many currently on the market, so not convinced that simply upgrading the fan will solve the problem. Any views on a combined fan and dehumidifyer? That is the only place in the bathroom with a power socket, other than the lighting circuit.

[Neelix]

Really interested in this thread. Posted earlier about a similar problem we have on the decorator's forum because the amount of condensation has actually led to paper peeling off the ceiling. In Winter icicles actually form on the ceiling (masses of loft insulation up there) and bubbles now on the paper as it has dried out. Got good advice about addressing the decorating problem, but loath to redecorate without trying to fix the condensation problem first. Tested our very old fan and it is actually better and more efficient than many currently on the market, so not convinced that simply upgrading the fan will solve the problem. Any views on a combined fan and dehumidifyer? That is the only place in the bathroom with a power socket, other than the lighting circuit.

What heating do you have in your bathroom?
How long does the fan stay on ?
Do you get decent airflow under the bathroom door ?

[moderator2]

I have split this from the other thread so that the OP doesn't get notified of new relies. Original thread here https://www.ultimatehandyman.co.uk/foru ... p?t=108156

[ericmark]

Condensation can be as much to do with room design as to any extractors, the biggest problem is over bath showers, these often have a gap both top and bottom, so the chimney effect causes the water vapour to circulate around the room, so whole bathroom gets damp, with a shower cubical normally sealed at the bottom, so water stays within the cubical, even with a wet room, the water vapour stays in area of the shower.

With an over bath shower, we want the extractor to be as close to shower head as we can, don't want extractor dragging the vapour across the room, the big question is do we really want the fan to run when the shower is running? Once the shower has been switched off, then yes want the fan to run, but during the shower it is often making things worse dragging the moisture into the room.

As already stated, any air out, needs replacing, and where it is replaced from is important, the colder the air the less moisture it can hold, so getting replacement air from outside is good, except we don't want to get cold in the shower, another good reason why it should run as we leave the bathroom, not as we enter, but using a heat recovery unit can also cure the drawing cold air into the bathroom problem.

I may seem daft, but single glazed metal framed windows with catchment trays at the bottom and a small hole to outside was very good at keeping the room dry, as the moisture would condense on the window, run down the window and be directed outside, so in the old days the home was much drier, I am not suggesting returning to single glazed windows, but pointing out why today more of a problem.

My first house had hot air central heating, and every internal door had a vent in it to allow the air to return, the house would get very dry, so we had a tray of water in central heating air intake, and loads of plants, the second house once cavity wall insulation fitted, double glazing, and loft insulation, plus better sealed doors to outside, the whole house became more humid, father-in-law even worse as he cooked on gas, which produces water as it burns, so you need a cooker hood piped outside, but all the fans seem to push air out, tumble drier, bathroom, and cooker hood, no one seems to consider how to replace that air.

Again the heat recovery unit seems to be the way forward, even if not in the bathroom. This house now in my bedroom is showing 37% humidity, this is rather low, the last house was more around the 75% mark, and father-in-law with gas cooker was reaching 85% at times, worse than a tropical rain forest. Drawing air so moist into the bathroom is never going to dry it out.

Also be away any open flue fire running extractor fans can draw fumes into the room.

I have no problem with this house so hard to test my theories, but having a fan run for 1/2 hour when you leave the bathroom when you can leave the bathroom door open, seems likely the cheap option.

[penandink]

We have central heating in the bathroom - but tried to save money last year by not having it on until November. Big gap under the bathroom door and it is freezing in there at the best of times because it is fully tiled. There is an over the bath shower which one of us uses and partner takes long baths to ease a bad back. The extractor fan is at the opposite end of the room, and because it is a bungalow there is very, very limited space for any electrician, unless he/she is very small, to reach it and put in a new extractor fan over the bath/shower. The fan is put on after use, and the windows opened, because it is too cold to have it running whilst bathing. Water runs off the tiles and ceiling. It is the only room in the bungalow that has the problem. What I have found is that the quickest way to get rid of the condensation is to open the bathroom door entirely, and the door of the bedroom directly opposite, and open the bedroom window opposite the door and you can see the hot air escaping on the warmer side of the house, but it might be transferring a problem to another room. It is all about design of structures. Lived in a Council House for many, many years and never had any of these problems, but then baths were only once a week and there was no double glazing!

[Neelix]

You need to run the fan when using the bath or shower

[ericmark]

You need to run the fan when using the bath or shower

This was also my thought to start with, but that only works if the extractor is directly above the shower,

temp3.jpg (5.44 KiB) Viewed 879 times

when the extractor is away from the shower it drags the moisture into the room, allowing it to condense before it reaches the fan making whole room wet.

So it depends where the fan is, with the new heat recovery units

temp4.jpg (28.45 KiB) Viewed 879 times

the exchanger is built into the pipe, so it does not cool the room as much, and it is bringing in drier air from outside, in the main the fans only work in one direction, so once fitted it needs door closed to get the air flow in both directions, more expensive versions have two fans.

And since very little heat lost, it can run a lot longer.

[Neelix]

You need to run the fan when using the bath or shower

This was also my thought to start with, but that only works if the extractor is directly above the shower, temp3.jpg when the extractor is away from the shower it drags the moisture into the room, allowing it to condense before it reaches the fan making whole room wet.

So it depends where the fan is, with the new heat recovery units temp4.jpg the exchanger is built into the pipe, so it does not cool the room as much, and it is bringing in drier air from outside, in the main the fans only work in one direction, so once fitted it needs door closed to get the air flow in both directions, more expensive versions have two fans.

And since very little heat lost, it can run a lot longer.

Disagree about the fan location 100%

[ericmark]

Disagree about the fan location 100%

You are entitled to your opinion, but it would help if you say why. I have tried to explain why I feel the way I do, I have not simply said that's wrong, you need to do the same.

I looked at 4 homes, not many I know, only one had a problem, and I wondered why only one, what was different between it and other 3?

Well of the three, first had hot air central heating which made the home very dry, so can discount that one, second was a wet room, there were no shower curtains so the chimney effect was not there, and the extractor was above the shower head, and the replacement air came from a cold dry hall, as on the ground floor, it also had UFH but the fan and UFH rarely used, so main thing was the dry replacement air from hall and poorly fitting sliding door. The last has a shower door which seals at the bottom so no chimney effect, again on lower floor, but no fan, and no signs of mould, it dries fast as the humidity in the house is low, in bedroom at the moment 39%.

The one with mould problem was just outside Mold, but that's a red herring, the main problem was shower over the bath, and the glass doors only went down to the top of the bath, so the chimney effect resulted in whole of bathroom getting damp, and the design of the house resulted in the humidity being around the 65% some times a lot worse, so there was no dry air to replace any air pumped outside.

So we want a) to keep water to within the shower cubical when having the shower, and b) replace the air pumped outside with dry air. Sucking air from directly above the shower is good, but if the extractor is anywhere else, it does not what to run until after showering is completed or is will draw moisture into the rest of the room. Also the cubical needs to seal either at top or bottom to stop the chimney effect.

So I have detailed why I believe what I have said it true, no point just saying it is rubbish, you need to detail why you think what you have said is correct.

[Neelix]

I have installed many bathroom fans and have the knowledge. Sure the best position is over or near the shower but what is needed is the most air expected and dry air sucked in.

That’s also why cheap non timer fans are not the answer too

[penandink]

Just to update everyone who tried to help. 1) We didn't relocate the existing fan - which, it turns out, really shifted the air. 2) We couldn't leave it on when showering because the bathroom is freezing at the best of times being fully tiled. We have solved most of the problem by after showering, putting the fan on, opening the top windows, and using one of those window vacs to vacuum up water all around the tiles, bath and windows and putting on a small dehumidifier to clear any remaining excess. Thank - you once again for everyone's help.