Fan vent dripping

Postby acsimpson » Mon Feb 02, 2009 4:28 pm

I have a newly installed fan vent in a new ground floor toilet. There is an intermittent dribble of water coming out of the vent pipe.

The vent pipe leaves the toilet and goes into an adjacent cupboard before bending up through a flat roof, passing through a couple more bends to avoid a window and rising parallel to a drain vent another storey where it is capped at loft height.

Initially I thought it was caused by the boiler condensation pipe which the #*&% plumber had put into the top of the wrong vent, however this has now been corrected and we are still experiencing the drip.

Does anyone have any idea what would be causing this and more importantly what we could do to fix it?
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Simply Build It

Postby Steve the gas » Tue Feb 03, 2009 5:16 am


My fisrt thought is water vapour rises in the duct, then as it cools down it condenses back into a liquid H2O higher up in the duct. Can you put something in place to divert the drips/ collect them??

Steve the gas
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Postby acsimpson » Tue Feb 03, 2009 9:58 am

Thanks Steve,

Yes I realised last night while putting socks on the radiator in there to dry them that condensation was probably the answer.

I wouldn't be too keen on collecting the drips as I'd be concerned that they would accumulate and find a way out. When you suggest diverting the drips the only thing that comes to mind is adding an outlet at the bottom of the fan vent and running a pipe to the waste vent next to it. I would obviously need to make or add a p-trap to the pipe to stop any smell coming back from the waste pipe. Would this be an acceptable solution or should I be doing something completely different?

Thanks again.
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Postby htg engineer » Tue Feb 03, 2009 1:10 pm

Fit a trap to the vent pipe, - connect with 20mm/overflow pipe.

htg engineer
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Postby acsimpson » Tue Feb 03, 2009 4:08 pm

[quote="htg engineer"]Fit a trap to the vent pipe, ... connect with 20mm/overflow pipe.[/quote]

Thanks, The most convienient point for me to connect it to would be the adjacent waste stack. Would I need to put some sort of trap to seal stop air coming back into the fan vent?
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Postby acsimpson » Wed Mar 04, 2009 5:28 pm

My builders have tried to solve the problem by putting a "trickle" vent through the wall into the adjacent garage. While this hasn't completely fixed the problem it does now mean that there is cold air streaming into my toilet.

I would have expected with the tighter controls on insulation that builders have these days that this should not have been allowed, can anyone advise me on this?

And does anyone have thoughts on my earlier idea of putting a condensation drip catcher in and feeding the output into the drain vent pipe?

Thanks again for your help.
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Joined: Sun Jan 18, 2009 11:33 pm

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