Heat from vertical boiler flue

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Hi There,

I am currently experiencing problems with condensation in my loft. I have an upstairs combi boiler and the flue runs vertically through the loft space on vents out the top of the roof. When I feel the outside of the flue pipe it feels quite warm to the touch.

I spoke to a roofer recently regarding the condensation problem and he says that the boiler flue should be double skinned and if so then it shouldn't feel warm if I touch it. He says that this may be the cause or at least contributing to the condensation problem in the loft space, as it is effectively a heat source in the cold loft space.

Can anyone advise on this?

Many thanks.
 
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Heat sources do not cause condensation.
Is it meant to be flued like that??
We'd need pictures or exact model numbers.

If the flue is leaking products of combustion into the loft space, THAT would cause condensation.
 
Hi Chris,

Many thanks for your reply. I can't take any photo's at the moment but will do so and post them on here.

However, I can tell you the model number of the boiler. It is a Baxi 105e.

With regards to the condensation, would dry warm air condense when it hits a cold surface, such as the underside of the roof in the loft? I know that warm moisture laden air would cause this, but wondered what would happen with dry warm air, i.e. that radiated from the flue pipe.

Thanks.
 
A lack of decent ventilation in a loft will more likely be the cause at this time of year. Check the insulation isnt tucked right up under the eaves, blocking the vents.
 
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How many times do you have to ask this?

Please continue with your original thread otherwise there's a danger we will provide responses over and over without realising you're the same person!

In case it wasn't apparent the first time around; the heat from the flue will not be causing condensation (quite the contrary in fact).

Mathew
 
Mathew,

A appreciate what you're saying but I have been told by others that heat radiated from the flue could contribute to the problem. So you see my dilemma, been told different info by different people? However, I am now inlined to go along with what you say as this makes more sense to me.

Thanks.
 
That's somewhat missing the point. If you've had conflicting advice then by all means post to open it up to wider peer review (that's the beauty of a forum like this - we can all give and debate our opinions out in the open) but do this by following-up on your original post, not by starting a new thread on the very same topic and risk us all going back to square one.

I suggest you ask the people that claim the heat will be contributing to the problem to explain why.

Have you taken the measures suggested previously? (Blocking up gaps around the flue, ceiling, etc)

Mathew
 
No Mathew, as I never received another reply since your last response asking if anyone better qualified could advise on the safe use of expanding foam to seal around the boiler flue. I have used flexible filler around other gaps in ceilings e.t.c though so have made a start.

Maybe I need to open up another post in a more relevant forum regarding the expanding foam.

Thanks.
 
With regards to the condensation, would dry warm air condense when it hits a cold surface, such as the underside of the roof in the loft? I know that warm moisture laden air would cause this, but wondered what would happen with dry warm air, i.e. that radiated from the flue pipe.

Thanks.

The air in your house is not dry and when it permeates through the ceilings it is going to cool down and start to make the loft feel damp. Condensation will form on any cold surfaces. The flue is warming the air in the loft and so is helping to prevent condensation. Any big gaps around it though will allow large quantities of air to pass through from below and this will make the condensation problem worse.

The ways to prevent the condensation are to seal up any large holes in the ceilings and improve the ventilation through the roof space so that the moist air gets 'blown through' before it condenses. You could also install some more boilers and flues so that they actually keep the loft warm enough to stop the condensation.
 
Ha Ha Dumbrill, very amusing. Do you think 10 boilers with flues located in the loft space should be sufficient? :)

Anyway, I am planning on having some tile vents fitted early in the new year which will hopefully sort the problem.

With regards to sealing around the flue pipe where it enters the ceiling, is it ok/safe to use expanding foam to seal around this?

Thanks.
 
Is this a 105E with the Potterton twin pipe system?

We have found an instance of a Potterton (I think it was the 105E) with the twin pipe system running at maximum length where it was condensing inside the exhaust flue and the boiler had dangerously corroded.

In the MIs Poxi Batterton had not asked for the exhaust to be insulated, but in an uninsulated roof space it was producing lots of condensate.

It was a write off, we replaced it with a Vaillant.
 
Thanks tryitandsee, I am popping to Wickes later so will have a look.

simond, very interesting. I am not sure what type of flue I have but can go up and take a photo of it later and post it on here if that would help you or someone else identify the type.

Supposing it is the type that you mention, could I have the flue replaced with a suitable one or would this entail a complete new boiler and flue? As far as I am aware there isn't any corrosion in the boiler, it was serviced this year and no mention of it. It also looks ok to me with no sign of rust.

I will post a photo of the flue on here later anyway.

Thanks.
 
Thanks tryitandsee. I have seen no Nonsense Fire Grade expanding foam filler at Screwfix for just under 4 quid, so may go for that instead! :D

Anyway, here are some pics I took of the flue. Any comments would be most appreciated. I was particularly interested to see droplets of condensation on the rubber seal at the point where the flue goes through the roof. Is this normal?

Link to pictures.

//www.diynot.com/network/electroman68/albums/

Thanks.
 

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