Electrical Question

Any other ideas on how to fix a dripping bathroom extractor fan?

The extractor fan in our bathroom (1st floor flat) drips in cold weather. So far we have tried:

1) Fitting a new extractor. It died within 4 weeks due to the water coming through it.
2) Lagging the duct pipe up in the loft.
3) Investigating the duct pipe up in the loft to ensure it's not blocked.
4) Replacing the grille at the end of the vent on the outside wall (this had fallen off).

None of this has worked. Every person that comes to look at the problem suggests something different, and I'm now at the point where I feel I'm just throwing good money after bad as nothing's worked.

The point at which the fan exits the bathroom ceiling is lower than where the duct exits the building, so there has to be a rise on the duct pipe somewhere in order to reach the exit - it currently goes up from the fan diagonally about 4 feet before then travelling horizontally alongexiting the building.

It's now been suggested that we should consider f removing all the existing plastic ducting in the loft , replacing it with flexible ducting and an in-line fan, so that we can create a rise in the ducting down towards the exit. But I am concerned that we are still going to have to raise the ducting at some point to reach up to the exit , and therefore we will still get condensation coming back down towards the bathroom.

The thing that's really throwing me about all this is that about 5-6 years ago, we never had any drip problem. The only thing that's changed in that time is that we've had 2 new extractor fans fitted!

Can anyone possibly shed any light on this? I'm beginning to think this is an unsolvable problem!!


8 Answers

Best Answer

Hi Helbels, in a roundabout way the answer to your question is within the question!

You wrote "The point at which the fan exits the bathroom ceiling is lower than where the duct exits the building, so there has to be a rise on the duct pipe somewhere in order to reach the exit" - in essence that is the problem! the duct needs to have a high point higher than the wall/grille outlet to the fresh air.

This is the only way to stop condensation running back down the duct line and into the fan.

Whoever installed the ducting/fan orginally has not complied with building regulations as condensation in the duct is a known isuue, hence the need for the outlet to be below the highest point of the ducting. Seems strange that no one has mentioned this before?

The only other potential solution is to fit a condensate trap on the route of the duct at some point?

see; http://www.justfans.co.uk/condensation-trap-p-243.html

If this helps please click on "like"

Answered 16th Jan 2012

Electrical Safety Services

Member since 17 Oct 2011

basically your problem is the cold air from outside going into the duct and the warm air from the loft is causing condensation in the pipe and due to the fall in the duct its running into your fan.

There are a few solutions i can think of that will help prevent this.

The first is the outside grill. It needs to be a gravity grill not an open one. you can tell whether you have one of these by looking at the grill if it has flaps that only open when the fan is pushing air out you have got the right one. if no flaps are present this is a likely cause of your problem.

The other solution is a vent you can get that fits inside the duct ( i have only seen these for flexible ducts) and prevents the air returning down the duct from outside.

The last solution is a extractor fan that has a trickle system. this is where the fan constantly runs at a really low speed you cant hear the fan running (so it wont be annoying a night time) as this is constantly pushing air out it should stop the water building up in the duct .

i would try these solutions in order as the first is the most cost effective with the last being quite expensive hope this helps you solve your problem.

Whittaker Electrical

Answered 16th Jan 2012

D&C Electrical

Member since 13 Jan 2012

It sounds like you need a condensation trap. if you cant find one at your local plumbers merchants try (just fans ltd on line). You will need to run the condensation off through an overflow if you go down this route.
Hope this helps-Kevin.

Answered 16th Jan 2012

kevin cassidy building contractors

Member since 16 Dec 2010

i would suggest maybe a more powerfull fan and change the ducting for insulated flexible ducting, which is also aluminium which also helps in the reduction of condensation build up.

Answered 16th Jan 2012

D A Electrical

Member since 5 Mar 2009

has the outside grill got a backdraft shutter or cowl fitted to stop rain entering? also the duct if longer than 2m should be insulated to stop condensation (pre insulated flexiduct, foil covered is best) and make sure the run on timer is working, after light turned off the fan should run on for at least 5minutes to get rid of all condensation, have seen this before and its been because new fan had short run on time so worth checking, hope this helps

Answered 1st Jun 2012


Member since 28 Mar 2011

Hi, My first answer would be to lag it but as you mentioned that has already been tried and failed.

You didn't really say how long the run was from the bathroom room to the vent, but I'm guessing it is a relatively long run.

My next thought is that the fan you had fitted 5-6 years ago had a higher extraction rate than the bathroom fans you are currently fitting (perhaps a kitchen fan). It may be worth fitting a kitchen fan (providing it has the correct IP rating for its position in the bathroom), I dont know how much you know about bathroom zones but a Part P registered electrician will understand them.

The point is that the airflow of a kitchen fan is much higher than bathroom fans, therefore getting rid of the moisture before it has a chance to condence in the ducting.

Just a thought.

Hope that helps.


Answered 16th Jan 2012

Allan Lathan's Electrical Services

Member since 10 Aug 2010

Hot moist air from the bathroom definitely sounds like it is causing the problem as it condenses. Lagging the duct is a sensible option as it keeps the warm air warm preventing condensation, however you are still getting condensation so look at the duct and ensure there is a steady continuous fall out of the fan.

If an in-line fan is used, it can be mounted at the top point of the duct so a fall to drain condensation can be made both on the inlet and outlet side of the duct. Make sure however the inlet of the duct is over a shower or bath as the condensation that comes out needs to go somewhere!

Answered 22nd Jul 2013

leonard cole

Member since 3 May 2013

Ventilation in the bathroom is a very important issue because of the amount of air pollution, and especially water vapor. The bathrooms have excessive water vapor in the air. Excess air moisture in the bathroom is especially evident in the form of steamed glass and mirrors, but not only. Too much water vapor in the air leads to unpleasant smells and to problems with drying wet towels.
In order to ensure effective ventilation in the bathroom, natural ventilation should also be used in the bathroom ventilators, which are installed in the ventilation duct and support gravity ventilation. However, for the bathroom fan system to benefit, fresh air must be supplied to the apartment by using such solutions as: unsealing windows, fitting bathroom doors with ventilation openings.

Answered 30th Oct 2017

AJ Home Building

Member since 24 Oct 2017

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