Bathroom extractor fan

rjinski · 22 Oct 2019

Hi all,

I have recently replaced a bathroom extractor fan because of moisture build up and that the original was vented onto the soil vent plumbing work in the attic with an assumed air admittance valve...

I replaced an on wall for an inline fan and created a new external vent to the outside. I replaced a 21l/s fan for 68l/s (twice the recommendation for the size of room) however it still seems to be under performing. I've used insulated air ducting and the travel is about 2 meters from the room to the wall. The fan is on the top speed and is running on a timer for the longest time possible.

I am a bit at loss what else to try... Any recommendations or things to look for?

Thanks

Room inlet: https://www.amazon.co.uk/gp/product/B01G8DM5UA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Previous: https://www.amazon.co.uk/gp/product/B00MCLJJHK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
New: https://www.amazon.co.uk/gp/product/B01G8DM5UA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Taylortwocities · 22 Oct 2019

If you are trying to pump air OUT of a room, you must allow provision for at least the same amount of air to get IN TO the room. If you don't then the fan is trying to create a vaccuum.
Just a thought...

securespark · 22 Oct 2019

I sliced a fair chunk off the bottom of the bathroom door to allow a decent amount of incoming air.

rjinski · 23 Oct 2019

Thanks for the replies. There is about an inch clear of the door but the window (on the opposite corner of the room) is usually open too...

AndyPRK · 23 Oct 2019

how long is the fan running for ?

rjinski · 23 Oct 2019

AndyPRK said:
how long is the fan running for ?

30 minutes once the lights are turned off however it is rare through the day the fan turns off.

But, the perceived poor performance is immediately after a shower. The room would only really feel like a steam room if the shower was very, very warm on a cold evening with the old fan, however, every shower now has a strong sense of steam lingering in the room and the mirrors are really wet to touch (rather than just being... steamy?)

JohnD · 23 Oct 2019

shut the window.

show us a plan of the room, with the position of shower, fan, door, window.

rjinski · 24 Oct 2019

JohnD said:
shut the window.

show us a plan of the room, with the position of shower, fan, door, window.

Attached

ericmark · 24 Oct 2019

In resent years lived in three houses, one shower in bath, next wet room, and final shower room. Only the shower in the bath had a problem, so sat back and tried to work out why, and realised it was the glass doors which clearly had a gap between bottom of door and bottom of bath, which allowed thermals to develop that circulated all the moisture laden air around the room, the other two either no door or curtain in wet room, or door sealed at bottom new house in both cases it resulted in less air movement so water condensed and ran down a drain and was not retained in the room.

Switching on a fan after you leave the room helps to dry room as long as room is heated, but during the shower it sucks the moisture into the room. So a simple pneumatic push switch that one pushes as you leave the room and runs fan for 15 minutes clears moisture, same fan connected to lights drags moisture into the room. Fan on lights to suck away smells yes good, but to remove moisture it does reverse of what you want.

JohnD · 24 Oct 2019

Why is the fan so far from the shower?

AndyPRK · 24 Oct 2019

my layout is very similar, and it works ok,

rjinski · 24 Oct 2019

ericmark said:
In resent years lived in three houses, one shower in bath, next wet room, and final shower room. Only the shower in the bath had a problem, so sat back and tried to work out why, and realised it was the glass doors which clearly had a gap between bottom of door and bottom of bath, which allowed thermals to develop that circulated all the moisture laden air around the room, the other two either no door or curtain in wet room, or door sealed at bottom new house in both cases it resulted in less air movement so water condensed and ran down a drain and was not retained in the room.

Switching on a fan after you leave the room helps to dry room as long as room is heated, but during the shower it sucks the moisture into the room. So a simple pneumatic push switch that one pushes as you leave the room and runs fan for 15 minutes clears moisture, same fan connected to lights drags moisture into the room. Fan on lights to suck away smells yes good, but to remove moisture it does reverse of what you want.

So, it is a shower over a bath and I've had a suspicion that since the shower is fairly powerful and generally aimed to the end of the bath it is pushing the steam into the room rather than being stuck inside a shower cubicle...

JohnD said:
Why is the fan so far from the shower?

I didn't include the bath under the shower which basically runs along most of the side wall and I assume the original fan was mounted away from the shower to avoid building regulations "safe zones".

ericmark · 24 Oct 2019

Your trying to dry the room, so need to draw in dry air, and extract the wet air, drawing air in from house is only going to work if the house is dry to start with, the problem is we seal the house to stop it getting cold, then insist on breathing. And in some cases burn gas in the house which will also produce moisture.

It is all well and good saying a heat recovery unit is the answer, but they are expensive. So some common sense is required. If that fan was blowing air into the room with the window open then it would likely push out the moist air, but if it sucks then it's sucking the moist air into the room, which will make it worse not better.

I know it seems daft, but replacing the double glassing for single glassing with a trough and pipe to outside would remove the moisture.

But trying to keep within what is practicable, I would put fan on a pneumatic timer and switch it on when you leave, not while having the shower.

JohnD · 24 Oct 2019

rjinski said:
it is pushing the steam into the room

I really don't believe that is possible.

The bathroom will be full of steam (water vapour) from the shower mixed with the air.

The extractor takes some of that outside the house

more air enters the room from elsewhere (mostly through the gap under the door). Unless the rest of the house is a sauna, this new air will contain less water vapour than the air that has been taken out.

Where do you think this "steam" is coming from?

SFK · 24 Oct 2019

Uhm... isn't the issue that the air is moving straight from under the door and to the fan by the most direct route.
So you are moving all the air from inside the house, under the door and straight out of the fan.
And missing all the steamy air near the shower.

Ceiling based fan should be above where steam is most prevalent.
With route from entry of air to room to the fan via the steamy region.
Otherwise you will not move the steam.

To see if my guess is correct I would be tempted to try and seal door, (close it with towel at bottom) and open window an inch and see if any steam is removed (noting that air from outside will be cold and so cause more condensation).

SFK

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Bathroom extractor fan

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