Adequate extractor fan ducting?

[NickB_99]

Hello all.

I've had some building work completed today where two extractors have been provided from an ensuite and the main bathroom.
I'm expecting builder back tomorrow to request closing balance, so was hoping for some quick feedback.

I'm a little concerned that the ducting looks a little 'knocked up'.
Please see pic.

Untitled

• NickB_99
• 12 Oct 2009
• 2

It seems to function ok, but seems more lke something from Apollo 13 than an elegant solution I would expect from a builder.
The white hoses are connected with duck tape.
I'd be concerned that the solution won't last long

Is all this normal and I'm worrying unnecessarily?

Thanks in advance.

 

[Thermo]

could have been done with some proper ducting rather than a mixture of drainage pipe and odds and sods. would have looked better, been better and probably been quicker.

 

[stem]

Flexible ductwork connected with "duct" tape is normal practice, in fact that's what it's designed for, also there's no harm in using drainage components either, also fairly common and provides a good, substantial, low air resistance, well sealed duct. In fact it's probably overkill. (I assume there is some sort of cowl on the outside to stop rain entering)

However putting the exhausts from more than one fan into a common stack I'm not so sure about. For example, when only one fan is in operation, what's to prevent the extracted air taking the nice easy route straight through the tee and out of the inoperative fan into the other bathroom, instead of making a sharp 90 degree bend and forcing its way up the stack. Especially if it's windy outside. (even if backdraught shutters are fitted they are not airtight)

Inpractice, where two points share a common exhaust, it's normal to have one fan that is ducted to both rooms thus creating a negative pressure at both points preventing the above, however there isn't separate control for each room then, and a larger fan may be required to get the required extraction rate.

Also I don't see a condensate drain. Usually the ductwork from a bathroom rises from the ceiling below and then drops down at a sight angle to an outlet at the eves. Any condensation in the pipe then runs out via the grille outside. With the vertical stack going straight up that you have, without a drain, condensation will run down the vertical stack and sit in the ductwork, and in theory may even build up over time to the point where it may drip back into the bathrooms

Small bathroom fans don't have a powerful motor either and the air faces a 90 degree bend at the tee which will provide additional air resistance. Good duct construction uses gentle swept bends and tees.

So I think that the construction of the duct is fine as far as the components go, but the design is poor.

 

[gday2uk]

what's to prevent the extracted air taking the nice easy route straight through the tee and out of the inoperative fan into the other bathroom

Hot air rises?

It would be best if both fans came on at the same time anyway though.

Could they not have gone through the wall in the picture? Two core-drilled outlets with grilles would have been cheaper than that (looks like) 150mm tee, pipe and the lead slate on the roof to weather it all in?

 

[stem]

Hot air rises?

Indeed it does, but it's a slow gentle process, it can easily be blown off course by a fan. It's similar with water, hot water rises, but do just upstairs radiators get hot? no because a pump shifts the hot water around.

Also how long do you think it will stay warm for in a cold duct?

Back to the OP, here's a link to a condensate drain should you wish to show your builder. Insulation also helps reduce condensation inside the duct by keeping it warm when the loft is cold.

http://www.alertelectrical.com/Fans...ible-Ducting/100mm-Condensation-Trap-1440.asp

Could they not have gone through the wall in the picture? Two core-drilled outlets with grilles would have been cheaper than that (looks like) 150mm tee, pipe and the lead slate on the roof to weather it all in?

Now you're talking, unless the wall goes through to the house next door of course

 

[NickB_99]

Back to the OP, here's a link to a condensate drain should you wish to show your builder. Insulation also helps reduce condensation inside the duct by keeping it warm when the loft is cold.

http://www.alertelectrical.com/Fans...ible-Ducting/100mm-Condensation-Trap-1440.asp

Will speak to him about this and the design etc.

Flexible ductwork connected with "duct" tape is normal practice, in fact that's what it's designed for, also there's no harm in using drainage components either, also fairly common and provides a good, substantial, low air resistance, well sealed duct. In fact it's probably overkill. (I assume there is some sort of cowl on the outside to stop rain entering)

That reassures.

However putting the exhausts from more than one fan into a common stack I'm not so sure about. For example, when only one fan is in operation, what's to prevent the extracted air taking the nice easy route straight through the tee and out of the inoperative fan into the other bathroom, instead of making a sharp 90 degree bend and forcing its way up the stack. Especially if it's windy outside. (even if backdraught shutters are fitted they are not airtight)

I had thought the same, so I turned the main bathroom fan on and went to the other. Could feel no air flow at all coming back.
I prob should repeat the test vice-versa - will do that tonight.

Could they not have gone through the wall in the picture? Two core-drilled outlets with grilles would have been cheaper than that (looks like) 150mm tee, pipe and the lead slate on the roof to weather it all in?

There is no house on the adjacent wall and I did suggest to him originally whether it was easier to go out the side. The roof is a bit dodgy, so thought there was less risk. I guess he must of had his reasons tho.
Again, will mention this also.

Thanks for the detailed responses. You've all been very helpful.

 

[NickB_99]

Hello again all

Sorry to resurrect this one - but the saga is still going on with this ducting.

Currently only using the main bathroom (as ensuite still not fully ready) and this is producing (I think) condensation over the chipboard floor of the loft, which is now staining/swelling the chip board.

It seems to be running down the inside of the vertical pipe, finding its way out of the joint half way up and collects on the outside of the collar of the sandy coloured T piece (from the original pic).
He's had one go sealing the joint better, but there is still some water escaping at the joint and now also seems for some to be working back down and out the edge of the T piece.

On the roof of the house, there is a approx 1-1.5m of pipe protruding (I can see an end cap - tho are these prone to leaking rain?).

This seems to be providing a long length of cold pipe (especially in this weather!) to allow condensation.

He's coming back for another look on Fri.
Any suggestions what I should push for to have best chance of resolving?

Add condensate trap? Get him to take the roof vent out (but this would then have a visible vent on the front of the house)?
He suggested on the phone splitting the vents and putting a second roof one.
But given the level of condensation coming from only one active bathroom, I'm not sure this will help.

Help appreciated.

 

[Deluks]

That design would've worked if there had been one fan only, installed in the roofspace where the drainpipe is. The fan could've been activated by a pullcord, off the lighting circuits or using a PIR in each bathroom.

As for the pipe extending above the roof by over a metre, complete waste of pipe. This isn't a flue or soil stack so there should be no real protrusion at all, in fact the warm air is probably condensing back into water whilst in the outside (cold) section of the pipe and running back down.

The water you are seeing could also be rainwater running down the pipe from the outside, if the exit hole isn't sealed properly.

Did the builder also wire up the connections in the fans in the bathrooms? If so then you should be aware that any electrical work in bathrooms requires inspection, or self certification by the electrically qualified person that installed it.

Makes me think that he has a clue, but not much more than that.

 

[noseall]

Agree with Deluks, the ducting needs to be as short as is possible from the fan to the outside air.

Wrap all exposed duct pipe with 100mm insulation and you should alleviate the condensate problems.

 

[stem]

Currently only using the main bathroom (as ensuite still not fully ready) and this is producing (I think) condensation. It seems to be running down the inside of the vertical pipe, finding its way out of the joint half way up and collects on the outside of the collar of the sandy coloured T piece (from the original pic).

This seems to be providing a long length of cold pipe (especially in this weather!) to allow condensation.

Help appreciated.

Why are you asking the same questions again? These were answered when you were warned what might happen back in October.

I don't see a condensate drain. Usually the ductwork from a bathroom rises from the ceiling below and then drops down at a sight angle to an outlet at the eves. Any condensation in the pipe then runs out via the grille outside. With the vertical stack going straight up that you have, without a drain, condensation will run down the vertical stack and sit in the ductwork, and in theory may even build up over time to the point where it may drip back into the bathrooms.

Insulation also helps reduce condensation inside the duct by keeping it warm when the loft is cold.

Could they not have gone through the wall in the picture? Two core-drilled outlets with grilles would have been cheaper than that (looks like) 150mm tee, pipe and the lead slate on the roof to weather it all in?

 

[NickB_99]

Why are you asking the same questions again? These were answered when you were warned what might happen back in October.

Sorry, I thought there was more relevant information to update on - long pipe outside roof etc.
Also his suggestion to put another separate pipe out through the roof concerned me - I was after opinion if it was likely to fix it.
I suspect not, but wanted a more knowledgable view.

The original feedback is welcome and has not been disregarded.

As for the pipe extending above the roof by over a metre, complete waste of pipe. This isn't a flue or soil stack so there should be no real protrusion at all, in fact the warm air is probably condensing back into water whilst in the outside (cold) section of the pipe and running back down.

Thanks for this - wasn't sure if there was a min height he had to go out.
(+noseall)

The water you are seeing could also be rainwater running down the pipe from the outside, if the exit hole isn't sealed properly.

It looks like top section of pipe inside the loft is bone dry. Then there is a joint and watermarks visible below here and some water on pipe surface. So hoping a good roof seal!

Did the builder also wire up the connections in the fans in the bathrooms? If so then you should be aware that any electrical work in bathrooms requires inspection, or self certification by the electrically qualified person that installed it.

Makes me think that he has a clue, but not much more than that.

He doesn't do himself - he has a subcontract spark that is NICEIC. He did all my bathroom electrics.

Thanks guys.