Bathroom Extractor Fan Dripping

alexfire

I have a small bathroom which has had an axial fan fitted to a flexi pipe which vented into the attic. I was advised this should be vented to the outside and so hired a roofer.

He made a vent through the roof and replaced the pipe with a solid plastic 100mm soil pipe. During showering the fan seems to collect water on the outsides which I'm assuming may be condensation running back down ?

I've tried lagging the pipe with aluminium foil and sheep wool but it's still happening. Since it's collecting drops during the shower I'm unsure whether it's a power issue although I can't remember the old one doing that and this is a higher powered fan ...

Would really appreciate any support / advice.

Images:

https://ibb.co/MgwkRbS

https://ibb.co/1vLLtQf

fenwick458

bad design by the roofer, it needs a u bend in it really so that the "small" amount of condensation just stays in the duct, rather than dripping through the fan.
but i think completely covering the entire duct with rockwool will probably fix it, try that first. aluminum foil hasn't got any insulating properties as far as i know
a centrifugal fan mounted in the loft is much better by the way, they are many times more powerful, much quieter and tend to last longer. plus it would solve your condensation problem as there would be no direct vertical route for water to run down, you might find on certain days when it's raining and the wind is blowing in a certain direction, even the best fitted roof vent will allow water to get in and run straight into the bathroom

tacpot12

You need some properly insulated duct, and probably a condensation trap and drain. When I installed my improved ventilation for the bathroom I used items from the Polypipe Domus range, see here -> Domus Thermal Insulation Article (polypipe.com), including this condensation trap (with overflow) -> Domus 4" Rigit Duct Condensation Trap Electrical World
The condensation trap goes at the bottom of the pipe and you run some 22mm overflow pipe out of the eaves or gable end to drain the condensation outside of the building. 

grumbler

fenwick458 said:

bad design by the roofer, it needs a u bend in it really so that the "small" amount of condensation just stays in the duct, rather than dripping through the fan.

Well, I've seen a flexible hose in the loft that collected almost a bucket of water in an unintentional U-bend.

Jeepers_Creepers

 Does it drip even when it's running, Alex?

Does it 'draw' quite powerfully - if you, say, hover a sheet of bogroll near the grill, does it get pulled up quite firmly?

As you say, this seems to be a decent fan at 26 lps/ 96m3/hr. I was going to suggest fitting a more powerful unit, ideally in-line, in the hope that this would clear away any forming condensation before it gets a chance to drip back down, but I'm not sure now that would help.

As Fen says, lag that pipe properly, and keep the fan running for a good 5+ minutes after use to fully dry the pipe. 

The U-bend idea seems fraught to me - surely water would pool there, and then could pour out in a more dramatic fashion when full? I dunno.

alexfire

Thanks all for the responses. I've already spent a fair bit and so any changes I do make I want to be sure this time they're going to be long lasting.

The extractor sucks up well, although seems like it's only dripping when it's actually running (will see if I can open the housing to see if there is any deposited inside). Stays on for 30 minutes after the light is switched off.

I'll try improving the insulation as suggested and see how I get on. Otherwise the condensation trap makes sense.
I did also think about just moving the fan to the wall although seems a waste now and I'd somehow have to patch the hole in the ceiling

Jeepers_Creepers

Insulation is a good first step. If that pipe can get warm from the heat from the bathroom air going through it, and not instead be a lot colder like the loft, good chance it'll make a large difference.

fenwick458

Jeepers_Creepers said:

The U-bend idea seems fraught to me - surely water would pool there, and then could pour out in a more dramatic fashion when full? I dunno.

grumbler said:

Well, I've seen a flexible hose in the loft that collected almost a bucket of water in an unintentional U-bend.

from my experience the u bend method is very easy to achieve and works for most. if a bucket's worth of water collects in the bend then theres a bigger problem, I'd say rain is getting in from the outside, or if it is from condensation then it would likely have come from a continuously running fan, extracting <22°C Air at <75% humidity, and the ductwork ambient temp was continuously  >2°C, which is an extreme example.
I'd say 90% of ducts in lofts form small amounts of condensation in the wrinkles (on the horizontal sections and low points), it's just nobody notices it until you introduce vertical runs right down to the fan or grill so it can escape. It doesn't just continually build up either, it might only sit there until it warm up and then it will evaporate.
basically I think the main thing to avoid is exactly what the OP has, a vertical run from the roof to the fan. Even it if it is 100% insulated and theres never any condensation forming, theres still a chance rain will get blown in and drip straight down.

grumbler

fenwick458 said:

Jeepers_Creepers said:

The U-bend idea seems fraught to me - surely water would pool there, and then could pour out in a more dramatic fashion when full? I dunno.

grumbler said:

Well, I've seen a flexible hose in the loft that collected almost a bucket of water in an unintentional U-bend.

I'd say rain is getting in from the outside,

No, it wasn't the case. And, AFAIK, good insulation solved the problem.

or if it is from condensation then it would likely have come from a continuously running fan, extracting <22°C Air at <75% humidity, and the ductwork ambient temp was continuously  >2°C, which is an extreme example.

This makes no sense to me. Why <75%?  And even if the fan is off, it's just a natural slow flow of warm humid air from the house getting to a cold flexible pipe. Condensation is imminent and irreversible in winter.

I'd say 90% of ducts in lofts form small amounts of condensation in the wrinkles (on the horizontal sections and low points), it's just nobody notices it until you introduce vertical runs right down to the fan or grill so it can escape. It doesn't just continually build up either, it might only sit there until it warm up and then it will evaporate.

horizontal hoses are easier to insulate and to create a small slope with for water to leak outside if it collects in big amounts.

basically I think the main thing to avoid is exactly what the OP has, a vertical run from the roof to the fan. Even it if it is 100% insulated and theres never any condensation forming, theres still a chance rain will get blown in and drip straight down.

Unfortunately, that's a preferred option of many builders nowadays.

RelievedSheff

alexfire said:

I have a small bathroom which has had an axial fan fitted to a flexi pipe which vented into the attic. I was advised this should be vented to the outside and so hired a roofer.

He made a vent through the roof and replaced the pipe with a solid plastic 100mm soil pipe. During showering the fan seems to collect water on the outsides which I'm assuming may be condensation running back down ?

I've tried lagging the pipe with aluminium foil and sheep wool but it's still happening. Since it's collecting drops during the shower I'm unsure whether it's a power issue although I can't remember the old one doing that and this is a higher powered fan ...

Would really appreciate any support / advice.

Images:

https://ibb.co/MgwkRbS

https://ibb.co/1vLLtQf

We have the exact same fan and have a similar issue with it but only during certain weather conditions and certain temperatures usually in early spring and late autumn before we have switched the heating on.

Ours is condensation forming on the plastic casing of the extractor fan rather than condensation running back down the ducting.

Now that the heating is on and the room warm the dripping has vanished. It will come back again in early spring when we turn the heating off and the shower room is a bit cooler.

alexfire

RelievedSheff said:

alexfire said:

I have a small bathroom which has had an axial fan fitted to a flexi pipe which vented into the attic. I was advised this should be vented to the outside and so hired a roofer.

He made a vent through the roof and replaced the pipe with a solid plastic 100mm soil pipe. During showering the fan seems to collect water on the outsides which I'm assuming may be condensation running back down ?

I've tried lagging the pipe with aluminium foil and sheep wool but it's still happening. Since it's collecting drops during the shower I'm unsure whether it's a power issue although I can't remember the old one doing that and this is a higher powered fan ...

Would really appreciate any support / advice.

Images:

https://ibb.co/MgwkRbS

https://ibb.co/1vLLtQf

We have the exact same fan and have a similar issue with it but only during certain weather conditions and certain temperatures usually in early spring and late autumn before we have switched the heating on.

Ours is condensation forming on the plastic casing of the extractor fan rather than condensation running back down the ducting.

Now that the heating is on and the room warm the dripping has vanished. It will come back again in early spring when we turn the heating off and the shower room is a bit cooler.

Thanks that's interesting to know - I did wonder whether it was condensation forming on the casing rather than in the pipe. I'm going to try and improve the insulation anyway and see if that helps at all before trying a condensation trap.
If it does become a problem then I guess the less ideal option would just be to put it on the wall making sure the exit is lower tha the fan itself. 

Have you had any issues with the condensation tripping the electrics - that's my worry ?