Extractor fans

[GMM]

I will need to put an extractor fan in the bathroom before I finish it. The 'obvious' route will go through a stretch of (uninsulated) roofspace for about 2-3m before going through a plastic slate vent. This has me wondering if there could be a problem with condensation in the ducting and, if so, how to deal with it. I was thinking a downward slope all the way to the vent but this will inevitably form a 'U-bend' at the junction. Will this cause a problem in reality (ie I'm overthinking it) or should I plan for a less obvious route, involving a lot of scaffolding?

[Bill Wright]

I did roughly what you're doing in 2000 and never thought about condensation. There hasn't been a problem.

Bill

[Tim Watts]

I do not think it's worth worrying about - you tend to either slope the pipe down to the vent outlet or down to the extract inlet.

What you do NOT want is a place water can pool and go stagnant and be a breeding ground for germs.

Many places vent upwards to the roof - the amount of water that might run back to the fan is miniscule and not really a problem.

[Chris French]

In message , GMM writes

I did same sort of thing in the old house, ran along in the loft joined to a vertical bit of soil pipe to vent through the roof. Fan was inline mounted in the loft. I arranged it so the duct exiting the fan dipped down a bit before joining to the veritcal so any condensation didn't run down into the fan.

I decides that if there was condensations in the pipe it wouldn't be enough to worry about, and indeed there never was a problem with it

if you are worried you about it, you could do it the proper way and use a condensation trap. Covering the duct with some insualtion would help avoid it as well I guess

[spuorgelgoog]

You can get condensation traps for ducts, they have a socket for a drain pipe you run to waste.

Owain

[harryagain]

I had this very problem. It was from the shower cubicle. It depends on the weather. If it's cold outside, it's worse.

I put in a short vertical bit of pipe and then a downward slope to an outlet in the gable end of the building so the condensate runs outside. A bit of insulation on the vertical bit of pipe. I used 110mm drain pipe.

The alternative is some sort of drain on the pipe to catch the condensate (eg make a deliberate low point) and conduct it away to somewhere.

[GMM]

Thanks Bill - No problem in 15 years sounds like I'm over-thinking it, as can often be the case(!)

[GMM]

I guess my thinking was that most extractors only take the air/vapour/etc across the wall, so there's less opportunity for much to condense. In this case, a couple of metres of cold pipe could be quite an effective condenser. With an inevitable dip at the end of the pipe, it could all collect there. I was thinking more of the potential for leaks onto the ceiling below than anything else, as this sort of ducting doesn't seem to seal perfectly.

Since Bill's experience is that it doesn't caus a problem, presumably anything that collects evaporates eventually, one way or another.

[GMM]

Thanks Chris - It seems your experience is similar to Bill's, so it is probably a non-problem.

[sm_jamieson]

I know someone who gets condensation dripping from their fan ceiling vent, so it can happen. When I temporarily fitted the fan to test things out, the re was quite a lot of condensation in the pipe above the bathroom ceiling b efore the inline fan, just from the air in the room - but at that time ther e was no insulation around the duct. Anyway it looked as if that could prod uce a few drips from the ceiling vent. So for peace of mind I put in a cond ensation trap. I suspect in reality if the fan runs long enough it will dry out the pipe, but if the fan was switched off when the exiting air is still damp there co uld be an issue (spot the pun !?). Simon.

[Brian Gaff]

As an aside, why is it that even when fans are extracting, on cold days there still seems to be a draft coming in as well as being pushed out? Brian

[thescullster]

My 2c

General info

Look at the room size and air changes and make sure you get the right fan for the job. Vent Axia used to have a calculation/design brochure for fan and duct sizing. I used this for both main bathroom and small downstairs toilet and resulting extraction works well in both (toilet has long discharge duct run).

In en-suite shower there is only a through wall axial fan (in the property when I bought it) which is cr@p. It is difficult to swap due to tiling and tile availability, cable route etc so has been replaced 3 times with similar cheap but compatible model.

I still believe it's worth paying Xpelair level prices rather than going for shed quality, if you want to do the job once and forget it for a good number of years. The Xpelair fan I got for toilet IIRC cost about £50 but is decent quality and came with 5 year guarantee.

BES supply plastic duct with elbows etc. suitable for air extraction. This is lighter and more managable than 110mm drain piping and is available in sizes which match fan outlets e. g. 100mm o/dia.

Phil

[Tim Watts]

+1 on BES - they do have some very weird fittings that can be useful in awkward routes.

make very decent fans IME - I have a 100mm axial in line and it's been well behaved.

[ARW]

It may or may not cause you problems. I have seen it cause problems several times.

However the simple solution - one that is approved for NHBC new builds is insulated ducting.

It will cost you £5 to £6 per metre but is the the correct stuff to use IMHO. eBay will probably sell per metre cut lengths.

[rbel]

+1

[Tim Watts]

Interesting - must check that out...

[Chris J Dixon]

And me. Not cheap, but works really well, and is practically inaudible.

Chris

[GMM]

Thanks Adam. Never noticed it before but now you mention it, it's quite readily available by the look of things. By the time I do this job and the long run for the vent from the downstairs bog I might even use up a

10m roll from Screwfix.

[ARW]

If the long run for the downstairs shower does not require insulated ducting then I would suggest using rigid/smooth ducting if possible - either rectangular or round - as this will give a better air flow. Just ensure that there is a small fall in the ducting from the fan to the vent.