bathroom extractor fan: ducting, control, etc.

[Adam Funk]

We're going to have the bathroom ceiling insulated & replastered, & I'm thinking of having an extractor fan put in at the same time. I asked our plumber about it last time he was here & he recommended ducting it out the roof (the bathroom is in an offshot under a sloped roof, with a partly sloped ceiling to match) & said it was a job for a roofer or general builder rather than him. (He subcontracted a roofer to deal with the top of the balanced flue when he replaced our boiler.)

Anyone else tried this? Any specific recommendations for fans, ducts, etc.?

AIUI, there are a couple of ways to control the fan: from the light switch with a timer running after the light is switched off, & with an automatic humidistat. Any recommendations on that?

Thanks.

[Tim Watts]

Soler Palau for the fan, BES for the ducting (they do just about every adaptor you'll ever need). Roofing store for a roof vent that suits your tiles.

I took mine out through a soffit vent, but otherwise the same as what you are doing. The shower room has a tile vent already installed as there's no soffit there.

[Chris J Dixon]

Agreed. After recommendation here, I bought one of these:

Admittedly not cheap, but I was amazed by how quiet it was, I had to feel the air to be sure it was running. The airflow is far better than the (failed) cheap one it replaced. It can push-fit into the pipework, and is readily removable for cleaning.

Chris

[Theo Markettos]

TLC have a ventilation calculator:

Their linked page on ducting is handy too - the longer the duct, the larger fan you need to push air along it.

It's worth looking at an inline fan - they can be much more powerful than a ceiling mounted one, and quieter too.

You might also need a condensation drain, depending on how it's set up. Don't forget to consider how you'll prevent wind blowing through the duct.

Some of them have fast and slow modes. This can be an extra switch, or the humidistat. Humidistats are handy, but a pain if you get false triggering and there's no way to turn the fan off (eg somebody has to leave at 5am and wants to have a shower without waking the house)

Theo

[ss]

Use the isolator switch if needs be.

[John Rumm]

My preference is for an inline ducted fan, so you can stick the noisy bit out of the room. Controlled by a humidistat.

[Theo Markettos]

Is it compulsory to have an isolator switch, and put it somewhere accessible? If the fan is on the ceiling there's no chance of accidental contact.

theo

[Chris French]

In the old house I put an inline one in the loft, with flexible ducting, connected to a bit of vertical soil pipe exiting through the roof with a weathering slate.

I didn't put in a condenste trap IIRC, but i did have a dip in the pipe between the fan and the exit pipe to stop any running back to the fan.

I had a remote humidistat in the bathroom - which worked pretty well once tweaked, though occasionally in very rainy weather it would trigger.You can get more expensive ones that can accommodate the change in RH due to temp drop t night better I think.

I had a sperate switch to manually switch on, and an easily accessible isolator outside if I wanted to turn it ooff when it had triggered.

[Chris J Dixon]

With the Soler Palau fan, nobody is going to hear it.

Chris

[Lobster]

On 15 Sep 2015, Adam Funk grunted:

In addition to what others have advised, I'd say avoid going through the roof if you possibly can - that's always going to present the possibility of rainwater leaks at some point in the future, plus the chances of condensate running back down the ducting and into the fan or room. If you can get the ducting to a soffit or gable end wall (and have the ducting sloped toward it) that's generally a much better bet.

If it's definitely not physically feasible, it wouldn't stop me from installing it through the roof though.

[Andy Burns]

With their wall mounted designs the have rubber motor mountings and integral back-flaps, do the inline ones have that? Any need to worry about how it's mounted to prevent noise transmission?

[John Rumm]

You may want to maintain the fan... easier with the lights on as well, so an isolator is certainly a good idea.

[John Rumm]

If you have a remote humidistat then they normally have a sensitivity knob on them. Hence if you do get a false run due to weather etc, you can just tweak the sensitivity with the knob.

[Chris J Dixon]

Mine is screwed to a board across a couple of joists, and there seems to be no discernable direct transmission. The mounting bracket includes some rubber isolation material.

There is no integral shutter. I used

but I'm sure others are available.

Chris

[Chris French]

Yes, mine was like that. But I found that if I fiddled with it on the odd occasions it came on when not required then it wasn't quite right for normal operation (it was really only when it was raining fairly steadily/heavily at night and at the right temp that it would happen)

[tabbypurr]

+1. A simple fan straight out through the wall is usually fine.

Noise reduction: mount the case on rubber bits, and the motor on rubber bits. If you don't mind the price, get a bigger fan than strictly needed.

Control: automated control is annoying. A manual switch works fine IME. But that is in a dehumidified situation where the fan doesn't need to run very frequently.

And finally, if you can use an alternative such as locking the window a quarter inch ajar or opening it, do. Most bathroom fans simply don't need to exist.

NT

[Adam Funk]

That's the system we've been using! But the condensation isn't getting cleared fast enough, & it's cold during the winter.

[tabbypurr]

... exactly the same is true with a fan. As condensation clearers the average bathroom fan is not much cop. And both work by swapping warm indoor air for cold outdoor.

NT

[bert]

Yes - according to the instructions I received with mine - Manrose high speed in line fan. Two pole for non-timed, 3 pole for timed. This is belt and braces to ensure when it's off it really is off. Fan power requirement depends on length of ducting - mine was too long for the fan that was fitted originally. OP might like to get consider ceiling vent and light. In line gate can be fitted to prevent blow back though I've never experienced any problem.

100mm normally enough but you can go to 125 or even 150. Have a look at

Useful place to start

One thing about them their warranty did say fan had to be fitted by qualified electrician and they would require copy of certificate in the event of a claim - which is a load of bollocks.

[John Rumm]

That has not been my experience. Having fitted several over the years the difference between passive ventilation and forced for clearing hot wet air out of the room is quite marked. I would go so far as to say that in rooms with a decent shower, a fan is almost essential.

They do but in different ways. A window will allow air exchange in two directions, warm air out and cold air directly in. That tends to make for a bathroom that gets cold very quickly in the winter. With a fan, the ventilation is more controlled and only occurs when required rather than all the time. Also the ingress of cold air is not directly into the one room, but is made up from seepage elsewhere all around the house. So while heat is still lost, it does not result in the cooling effect being felt all in one room.