Flexible insulated ducting?

7 Jan 2010
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United Kingdom
I'm looking to install a new extractor fan, which I will be venting to an outside wall through a small roof space. The distance between the ceiling extractor and outside wall isn't very far - 2m at the most.

I want to be sure I don't get any moisture collecting in the ducting and then dripping back into the fan as the air in the roof space above the bathroom is likely to be very cold, especially at this time of year.

Should I use insulated ducting or would simple flexible plastic ducting be fine? Exactly what is insulated ducting? Is the the type made from aluminium?

The extractor I'm considering getting requires 120mm ducting and I would appreciate any pointers to the best type to get as I'm struggling to find anything described as "flexible and insulated".
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Well insulated ducting is all very well and it may help but really you should fit a 'condensation trap'.

All is explained in this thread: //www.diynot.com/diy/threads/nice-soil-pipe-bodge.417635/#3241438

Hopefully you'll reply unlike the ungrateful fecker in that thread.

If you look at the insulation around a length of insulated ducting it is pretty thin and consequently not very effective. You could do a much better job by wrapping some rockwool around it with some tie wraps.
For a 2m run, I'd lag the duct well with cosywrap, and then bind it up with cling film to keep it there......bloomin' awful stuff but it works well.
John :)
Thanks guys. I confess the link has got me even more worried about the possibility of condensing water leaking back into the fan.

I'm assuming that by lagging the 2m ducting as much as possible, this should minimise, if not prevent condensation occurring within the ducting and so avoid the issue, or is there always likely to be some condensation, regardless of what I do.

Fitting a condesation trap isn't possible due to the inaccessibility of the roofspace above the en-suite. There is no way in from above and I'm even going to struggle to run the ducting from the outside wall to the extractor - I will have to do this through the hole I make in the outside stonework.
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There will be condensation, it's just a matter of degrees.

If you're using an in-line fan, just make sure that the fan is at the highest point.
I had problems with condensation collecting in the flexi ducting so I fitted a condensation trap that drained off the water and that solved all the problems.
A bit more work but worth the effort.

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