water in ducting from shower extractor fan

10 Jan 2008
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United Kingdom
first posting on here so be gentle.
installed an extractor fan in bathroom couple of months ago. went into loft at christmas and noticed there was quite a large quantity of water in ducting. emptied water out and checked couple of days ago and water in again.
the ducting is probably about 4 metres long and goes to a roof vent in roof tiles (closest i could get ducting to outside due to new extension on side of house. bathroom now in middle of house and it has a flat dormer roof)
i have set the fan timer to 10 minutes after it is switched off to give a chance to clear room.
any help on this situation would be gratefully received.
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leave the timer on longer

and flop loft insulation over the duct to keep it warm throughout its length. the condensation occurs because the surface of the duct is colder than the moist air travelling through it.

If you can tilt the duct so that (apart from the bit coming up from the bathroom) it tilts downwards towards the exit, any condensation should drip out instead of accumulating.

It is all to common to find this.

Flexible ducting is a cursing invention leaving low spots everywhere.

It is a council spec to install a condensation trap to take any standing condensation away to a drain. It is common to put overflow pipe from the trap out through the facia (similar to tank overflows).

If the roof vent is a long way from the fan, this may not be easily achieved - But thats where forward planning and design comes in.

MY wholesalers stock the traps as standard.
ok. thanks
i will put insulation around the ducting and see if that helps. i cant lower it any more because it comes from ceiling level in bathroom to vent in roof. it is angled about 45 degrees.
the fan is a distance away from vent so i would the condensation trap be unsuitable fo me?
also, i filed to mention in first posting, that since i installed this, my bathroom seems to be very cold. i suppose the vent is blowing cold air in when the fan isnt in use.
could this also cause a problem with the steam escaping. possible back draft. can i cure this? should i add another fan, possibly an inline one?
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hi i have a similar problem , in couple years i have replaced 3 extractor fans, one just stopped spinning, latest one got condensation on the connected wires, and I'm looking of getting a new fan but thought maybe you can advise me which one etc.

I have inlcuded the image of my situation, as the ducting goes nearly straight above the fan, not at the side of the roof,

this is ex council flat so the loft and roof belongs to the council and can not do any changes,

so there is a three 'chimneys' in my loft , one-my neighbour from below uses, another- from my kitchen chimney, and last one I have connected the shower extractor fan


here the fans I'm thinking of choosing from:


the one I just had : http://www.screwfix.com/prods/92561...nt-Axia-Silhouette100T-Axial-13W-Bathroom-Fan

many thanks
if you mean you are getting condensation in that flexi trunk, flop loft insulation over it to stop it getting cold.
I will wrap arount the insulation on Ducting Hose, I will connect 100MM 4” CONDENSATION TRAP, between the hoses, nearer the fan , but maybe somenone could sugget me which fan I should choose:

the cheapest with timer or something like:

the second picture looks like a better one

generally go for a Centrifugal fan if you can afford it, they are quieter and more powerful than equivalent Axial fans

either run it with a humidity switch or have it come on with the light and a 20-minute overrun

if you have showers or leave wet towels in the bathroom it will take a long time to dry out

the horizontal trunking route will IMO be less troublesome than putting it through the roof
you say you have a 4meter run now iv never had this prob before but i belive the max duct you should run is 3 meters well so say the manufactures manuals.
Rigid duct is far more efficient than flexi, and also makes trapping condensate easier. You can use a short length of flexi for the final drop through the soffit if needed.
ok, I see, at the momebt I have a rigid duct, so I will get that trap and a a short flexi duct
many thanks
And ensure there is a way for warm air to get in the room to replace that extracted from the room. Gap under the door is easiest way to achieve it.
Out of interest, as I've never tried it, has anyone ever fitted a heat recovery unit to serve only the bathroom? It would seem like the ideal way to remove condensation from a sealed room without too much heat loss.

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