Ensuite Extractor/vent flexi-pipe

[tmcw]

Not sure if this topic might be suited to a different forum, but I'll try it here...

I was up in the attic today, and was looking at the vent pipe for the ensuite, and noticed that it was sagging in a couple of places. Turns out there was water in a few spots.

Anyway, I went to the end of the pipe, and noticed that it just ends where you can see in the picture, going down onto what looks like plasterboard. Is this normal building practice? I understand there wouldn't normally be a huge amount of water gushing out of there, but there was a fair bit today, when the water in the sags was displaced.

There are vents on the underside of the fascia, I can see them from outside the house, so are these vents supposed to disperse moisture from the flexi-pipe?

I was thinking of connecting the flexi to the toilet vent, which is vented through a roof tile, but maybe sewer smells could then come into the ensuite through the flexi-pipe?

Or is my only other option to ensure that there is a gradual slope in the flexi-pipe so that the moisture extracted by the fan is dispersed gradually?

Untitled

• tmcw
• 16 Jun 2011
• 1

Untitled

• tmcw
• 16 Jun 2011
• 1

 

[Richard C]

There should be no water in the extract duct. Unless you have something special by way of an extract fan, that length of run is excessive, even good fans will only go up to 3m duct length; it’s far too long & the air velocity of most domestic fans will drop dramatically after just 2m. Moist air is condensing in the duct, hence the water your finding; in winter when the loft is cold it will be far worse. You’re probably growing all sorts of nasty bacteria in the duct, including Legionella which is a serious health hazard. You need to either reduce the duct length to within the fan specification or buy a seriously powerful extract fan that will cope.

 

[mointainwalker]

Suggest you replace it with rigid PVC pipe.

This will not only improve the efficiency of your fan because all the "waves" of the concertina create a lot of friction but , as long as you arrange a negative gradient towards the outside, any condensation will trickle away instead of settling in the ridges of the concertina.

 

[Richard C]

Suggest you replace it with rigid PVC pipe.
This will not only improve the efficiency of your fan because all the "waves" of the concertina create a lot of friction.

Unfortunately I suspect that the fan manufacturers velocity specs are based on “smooth ducting” in any case.

 

[mointainwalker]

Possibly, but then, we don't know what fan he has. Even a centrifugal unit will suffer from condensation in a cold attic and this rubbish concertina piping.

 

[tmcw]

Thanks for the replies.

The flexi-pipe is about 4 meters, and the fan is GFAN4T link

I couldn't see it mentioned anywhere about length of pipe that can be used, but imagine 4m is probably too much for it. Says it can do 93m3/hr.

I saw a similar setup and question asked on another forum since link

Any way of connecting to the sewer vent that's right beside the fan?

 

[Richard C]

Any way of connecting to the sewer vent that's right beside the fan?

Problem is that’s a two way "air traffic" from the sewer & certainly isn’t permissible under UK Building Regs. No idea what’s permissible in the Republic.

 

[mointainwalker]

The fan doesn't state what type, but for 15 pnds is will be a simple axial one and they are generally said to only be good for 3m or so.

Having said that, I have wondered what is supposed to happen to the air at 3m. If it is in a negatively inclined pipe, then I would expect it to keep rolling regardless.

Don't connect it to a sewer outlet. That would be just plain daft.

 

[tmcw]

Thanks again.

No, I wasn't going to connect directly to the sewer vent, I was just wondering if there was a tee-peice that could be installed on the pipes with a 1-way valve that would open when the fan was on, close when fan is off to prevent sewer smells coming into the ensuite.

I'll look at replacing the flexi with a hard pipe and install a grill at the soffit. I suppose if the fan can lift the moisture a couple of feet, the gradient can take care of any moisture that condenses in the pipe. My biggest concern is the moisture that's not exiting the soffit completely.