Bathroom Fan Ducting Help

[bummer007]

Hi guys,

Long time lurker, first time poster!

I think this is the right board to post this in as it's related to electricals.

I moved into a 5 year old house in July and the fan in the en-suite has been fine until this week when water started dripping out and it created a water mark around it.

Untitled

• bummer007
• 4 Feb 2014
• 1

Having been up in the loft to inspect, I found the setup shown.

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• bummer007
• 4 Feb 2014
• 1

As you can see, the ducting goes horizontal immediately after the fan and then vertical to a tile vent.

The horizontal part appears to be pooling quite a bit of water which seems like it's corroding the ducting and so it's within the insulation.

Therefore I'm keen to replace it all and hopefully stop this happening again.

Was the issue one of the below or a combination of them all?

1) Slack within the ducting leaving it vulnerable to condensation collecting.

2) The horizontal section sloping toward the fan as opposed to away from it?

If so, what's the best way to avoid this rehappening when I redo it?

-I read that I should use rigid piping as opposed to flexible ducting, would that make a difference?

-Should I tilt the horizontal section away from the fan as opposed to towards it to prevent condensation from flowing back out of the fan?

Based on the above, a 90 degree elbow straight from the fan into a slightly downward slope and then another 90 degree into a vertical to the vent?

Any advice appreciated as this is the first time I've ever needed to fit ducting.

(Can anyone point me at the best materials to use/where to get it from?)

Edit - Sorry, seems to not want to let me post the image the correct way but hopefully it makes sense!

 

[RF Lighting]

The flexiduct you have is far too long, so as you say, has allowed condensation to pool in the horizontal section of it. Also flexiduct has loads of ridges in it, which condensation likes to form in.

The best thing is to use to replace it is a straight piece of rigid ducting from the fan straight up to the vent on the roof.

It'll keep condenstaion to a minimum, and any small amount that does form will not be able to pool and cause an issue.

You can buy proper ridgid fan duct from most DIY places, or you could use a piece of 110mm drain pipe which you can get at every builders merchants and DIY store. You might evan be able to find a bit for free!

Tape the duct to the fan and to the roof vent to prevent any air leakage into the loft. I find aluminium adhesive tape best for this.

Then the most important thing you must do is wrap the duct in insulation. 100mm thick would be great, and make sure it's all completely covered. You can secure the insulation to the ducting with string.

This will virtually cure any more condensation problems in the future, and is a nice easy DIY fix.

 

[bummer007]

The flexiduct you have is far too long, so as you say, has allowed condensation to pool in the horizontal section of it. Also flexiduct has loads of ridges in it, which condensation likes to form in.

The best thing is to use to replace it is a straight piece of rigid ducting from the fan straight up to the vent on the roof.

It'll keep condenstaion to a minimum, and any small amount that does form will not be able to pool and cause an issue.

You can buy proper ridgid fan duct from most DIY places, or you could use a piece of 110mm drain pipe which you can get at every builders merchants and DIY store. You might evan be able to find a bit for free!

Tape the duct to the fan and to the roof vent to prevent any air leakage into the loft. I find aluminium adhesive tape best for this.

Then the most important thing you must do is wrap the duct in insulation. 100mm thick would be great, and make sure it's all completely covered. You can secure the insulation to the ducting with string.

This will virtually cure any more condensation problems in the future, and is a nice easy DIY fix.

Thanks for the reply and glad it sounds pretty easy!

The vent isn't directly above the fan so it will need some sort of horizontal section but sounds like if I use solid ducting which is insulated, it should be fine!

 

[Taylortwocities]

To be absolutely sure, add a CONDENSATION TRAP as well.

 

[SFK]

bummer007,
Looking at your images I had exactly the same issue (extractor fan into loft, flexible pipe, fixed pipe exiting house through roof tiles).

I first replaced the flexible pipe with a fixed pipe. But I still had water returning down the pipe to the fan (although now it did not leak out and drip in the loft).

On re-inspection I found that little water was condensing in the pipe section that was in the loft. Most of the water was condensing in the fixed pipe that exited the house through the roof tiles and the main condensation point was at the roof tile boundary (presumably where the outside of the pipe was the coldest).

So I then had to add a condensation trap. This was added as low in the loft as I could put it. The main issue with the condensation trap was working out how to get the waste pipe from the condensation trap to the outside where the water could drip out.

I wanted to add my comment as I had to do this as two jobs, and there is a good chance both the above suggestions are correct and both should be done at the same time.

Regards SFK