can I "extend" my boiler flue?

[johnhenstock83]

hi all,

 

a bit of a short question on our boiler flue.

 

we currently have an extension shell with a 3.6m wide opening (for bifold) and 3 skylights (1200x800). the boiler flue sits at the back of the house, "in" the extension. because it's not closed at all and we don't spend any time there, it's not really an issue, the exhaust fumes don't hang around and are gone almost as quickly as before.

 

the main issue we're having is that because of the cold, the fumes condense excessively on the roof joists and chipboards, which are wet most of the time and have started showing some signs of mould (local).

 

my question is whether I can hang a pipe off the roof joists (easily done) and basically "extend" the flue plume kit to the edge of the extension. for the record, this is not tempering with the actual flue, it's placing a pipe at the end of the black bit, where the gas comes out, to "move it" from the back of the house to the end of the extension.

 

thanks

[ProDave]

Is this extension "work in progress"?  What will happen when it is complete?  The flue will have to be properly re routed or the boiler moved.

[johnhenstock83]

the extension is indeed work in progress and it's just a shell with plenty of holes, so ventilation is there. there's also a CO alarm between existing door/window, so should there be an issue, we'd know, but the fumes are ejected away from the house and disappear into thin air.

 

the only issue is that when it raises, all the water vapour in the fumes condenses on the joists (roof is still exposed) and I'm afraid that's destroying it long term. a few weeks wouldn't be a problem, but we've had some delays with the builder, it's been winter months now.

 

the boiler is planned to be moved before the extension is finished, we just can't do it yet due to planning (as in coordinating builders) issues.

 

thanks

Edited February 8, 2023 by johnhenstock83

[JohnMo]

Couple of issues

 

The steam being ejected from your flue indicate your boiler is NOT condensing so your boiler return temp is too high for efficiency.  Some fine tuning of the flow temps would improve condensing of the boiler and way less steam being emitted from flue. Ideally you need a water return temperature of less than 54 degrees

 

 

Second you need to be gas safe to install or modify the flue, so a job for the plumber.

[johnhenstock83]

it does reduce significantly once it runs for a little while, could it be a case of not reaching a required temperature for condensation or something like that?

 

also, in slightly better weather, the fumes are barely visible. isn't it the case that water vapour condenses, hence you can see the steam?

 

what's the water return temperature, what's causing it and can I set it up myself? I'm fairly technical and I have the boiler manual.

 

understood that only a plumber should touch the flue, I'll look to cover the immediate area above the flue with some celotex or plywood.

[PeterW]

Plume management kit would do it out of the side if possible but I would just put celotex on the ceiling and be done with it 

[JohnMo]

1 minute ago, johnhenstock83 said:

case of not reaching a required temperature for condensation or something like that?

No, the condensing occurs within the boiler at the heat exchanger, steam is converted to water (latent heat is captured), condensate drains out of the condensation pipe to drain.

 

4 minutes ago, johnhenstock83 said:

slightly better weather, the fumes are barely visible 

Mostly to do with dew point at the exit of the flue, steam get absorbed quickly by the air 

 

5 minutes ago, johnhenstock83 said:

what's the water return temperature, what's causing it and can I set it up myself?

Your controller or screen on the boiler should show return temps, as you say look at your manual.  Basically reduce the your boiler flow temp will directly affect your return temp.  Normally a bit of a balancing act. Remember it's not the flow temp it's only the return temp you need to manage.

 

The lower the flow the better the boiler efficiency.  My return is about 30 degrees or below due to UFH, boiler efficiency in the region of 115% for heating.

[Radian]

21 minutes ago, johnhenstock83 said:

what's the water return temperature, what's causing it and can I set it up myself? I'm fairly technical and I have the boiler manual.

 

First, what kind of boiler? Combi? System or Heat-only? And how many kW? This will all be stated in the manual.

[johnhenstock83]

thanks all. I decided I'll buy a piece of celotex and cover the affected area, cheap and easy solution, safe as well.

 

having said that, I'm intrigued by the boiler efficiency discussion. the burning temperature is set at 75 degrees and when I try to change it (I wanted to lower it slightly, as per general advice), the screen flashes "no" (glowworm c30). I figured out, by reading the manual, that the installer locked the temperature, hence not too easy to change it.

 

we have radiators with TRVs fitted around the house, they're all on max. if the house is cold-ish and I turn the heating on, it feels nice and cosy in about 10-15 minutes, so the system works ok. is there anything I can do/alter/measure to start playing with some (safe) efficiency settings? worth mentioning that boiler is on 20 deg during the day and 19 deg at night, bills never went above £180/month with the current variable prices, so something MUST be ok.

 

I just went outside to check and once the boiler reaches around 70 deg, this is what the plume looks like. does this look ok to you?

https://file.io/W4XthvF19Hhs

 

the problem is that the house is well insulated and it takes quite some time for the temperature to drop (could be 1-2 hours). by then, the circuit cooled down and when the boiler starts up again, the fumes are "white" because the boiler is not at the optimal temperature for condensation. can that be true?