Bathroom Air Flow - Window open or shut when showering with extractor fan on?

BobT36

We have some sort of mixflo extractor, yes (a cheaper-end manual on/off). I'm in a rental so don't get to choose. 

It's working way better than none at all, though! Huge difference in moisture during and after shower. 

I've been experimenting a bit, it does indeed seem that having the bathroom window SHUT, and setting the hallway window (just outside the bathroom door) on vent, results in WAY less steam and moisture than the bathroom window fully open. (this is with the fan on, of course). 

What works even better is if we have the heating on at the same time, presumably that the bathroom tiles and air are warmer, so moisture gets sucked up out of the ceiling extractor, rather than settling on the tiles / ceiling. 

It quickly clears afterwards (with the fan still on for a good hour or two), with ONLY the window glass still having moisture. I can only surmise that my hypothesis about the airflow direction (and temperature) is helping.

This is in comparison to needing the bathroom AND hallway window fully open, AND a dehumidifier running literally all night, and still waking up to moisture still on the tiles! Before getting the fan. The extractor seems to have next to no effect on the electric use, too. Whereas the dehumidifier was a hefty thump to the pocket. 


The only other thing I can think of trying is seeing how it goes with the bathroom window on vent, rather than fully open / shut. 

ThisIsWeird

BobT36 said:

The window is a long one and stretches over to where the toilet is, but only the shaded bit (blue) opens (top

With your layout, Bob, I'm not surprised at your recent findings.

No house is going to be so airtight that an extractor fan ain't going to work! (Well, 99.999% of houses anyways.)

You can test whether an extractor is extracting by placing a tissue paper close to it - see how sucky-up it is. You can compare suckiness with having both window and door closed, window open, door open, hallway window open, whatevs.

I think you'll find there's little actual sucking difference between them. Even with the bathroom window and door shut, enough will still seep through all around the door, and this will do the best job of flushing the 'steam' out of the bathroom. Such a seepage will create a gentle front of clean warm air from the house, and hopefully keep that end of the room drier. It'll be flushing the showering air out from that end, which is what you want.

Opening the window - especially where yours is located - no. It'll cool the air, making it unpleasant to be in, more visible, faster condensing-out, wetter on walls, but will also swirl the air around so's it doesn't get extracted properly. I wouldn't even have the window on trickle, until you have finished extracting. 

Door shut in our shower room during showers, fan obviously on. With still some misting of the mirrors usually remaining afterwards, I leave the fan going for whatever - 15 minutes (until we remember to turn it off), but with bathroom door left ajar. When fan is turned off, bathroom door is left fully open so the room continues to 'air'.

radox2608

Good question. I've often thought about the window open or closed dilemma myself

I thought I'd just mention that you can buy extractor fans with a humidity sensor so that they come on automatically when the humidty in the room is above a certain level. I've always thought this is really want you want rather than just relying on the fan being on for a certain period of time. They also come for a fixed period when triggered by a light circuit and the one I got about 10 years ago also has vents on the front which automatically close when the fan is not running thereby preventing backdraughts. Wasn't much more expensive than the more common extractor fan too.

I've never had a problem with damp patches in my bathroom and its reassuring when you hear it staying on longer on cold winter mornings when it's obviously having to work harder to get the humidity level down. I'm pretty sure I'll try to get another one like this should the current one fail.

BobT36

^ Yup. Can't change it in a rental though. Regardless, having a fan (even a crap one) has improved the situation a LOT. I was cleaning mould on the ceiling above the toilet at the right side every few weeks, before. Haven't had to do it once since the fan was put in. 

I do the exact same as ThisIsWeird where I have it running during shower, then leave it on with the door ajar after shower for an hour or so, then open the door wider to air out, and turn it off as soon as the tiles / ceiling are dry. I wipe up any remaining condensation on the window the next morning. 

After further testing..
Bathroom window wide open, fan off - Absolutely terrible, lots of mould, still condensation in the morning unless run a dehumidifier literally all night (ouch electric!) and bloody cold with having the bathroom & hallway windows open all night! 

Bathroom window wide open, fan on, heating on or off - Ok. Certainly better than no fan. Lots of steam though and takes a good while to clear, also cold bathroom! 

Bathroom window CLOSED, fan on, hallway window vented, heating off - Better! Surprisingly much less steam in the bathroom and condensation clears quicker. Can close hallway window around an hour after showering. 

Bathroom window CLOSED, fan on, hallway window vented, heating on - This seems to be the best. Even less steam, even on a cold winter day the tiles and ceiling is clear within 2h afterwards. Can close the hallway window around an hour after showering. It seems heating the bathroom for a bit first helps the condensation be sucked out rather than sticking to the cold tiles.


So yes, it's not perfect, but with this config keeping the bathroom window CLOSED certainly helps. The fan draws more air from the house / hallway window (immediately outside the bathroom) and sucks it THROUGH the bathroom and out of the vent above the bath/shower. There's still a bit of a wet patch above the toilet on the right (only in winter), but this quickly clears within an hour, and the tiles are clear within 2h, where I can then turn the fan off. 
I have one of those British Gas electricity monitors and the extractor fan electric use barely registers, whereas the dehumidifier (now longer needed) blew it into the next set of digits! (Even though I've got a decent ecoair zeolite one). 

ThisIsWeird

Thorough testing, Bob! Except for one option...  

Try, 'Bathroom window CLOSED, fan on, hallway window also closed, heating on (if it's already on).'

Your whole house will almost certainly (certainly certainly) provide more than enough air supply to serve your bathroom extractor, and this will be air warmed to your house's ambient, so should do a slightly better job than allowing cold air in via a nearby hallway window.

It may also be better - worth testing and comparing - closing the bathroom door again after you finish showering, and whilst the fan continues to extract for a further hour or so. If the door is left ajar, the main air flow into the bathroom will avoid the loo end. I think the steady, more-dispersed air flow from all around the door frame will provide a slightly better curtain of air travelling up the whole bathroom, gently flushing out the cond.

markin

Most basic fans are 10w, or 30w for a inline fan, I now use a dehumidifier as its cheaper than letting all the hot air out a window. Electric heated house.