condensing flue through cellar roof to above-ground ?

Mexico_quest · Oct 21, 2019

Hi all, can anyone advise if it's possible to route a flue from a condensing boiler in an underground room up through the ceiling (15" thick) where it will come out above ground on a flat surface ?
And from there it will extend up the side of the house, as in this picture ?

centralheatking · Oct 21, 2019

Just refer to the manufacturers specification for your chosen boiler you will also need to
pump the condensate discharge as well. Manufacturers instructions super seed any GSR
regulations but should conform. As to the wisdom of your plan wait for the experts on PF to agree and comment on the principle.
centralheatking

gmartine · Oct 21, 2019

Should be okay as long as it's well supported, MI's will dictate how long and how many bends.

snowhead · Oct 21, 2019

The flue use will have to be suitable for external use.
Not all manufacturers permit use of third party flues on their boilers.
Not all manufacturers make flues suitable for external use, other than the terminal extending from the building.

So it will be a case of finding a suitably sized boiler who's manufacturer also make /permit use of long external flues.

Next, the hole needs to be formed so that it is watertight and allows movement of the flue due to possible expansion and doesn't allow water to leak into the basement room.

centralheatking · Oct 21, 2019

snowhead said:
The flue use will have to be suitable for external use.
Not all manufacturers permit use of third party flues on their boilers.
Not all manufacturers make flues suitable for external use, other than the terminal extending from the building.

So it will be a case of finding a suitably sized boiler who's manufacturer also make /permit use of long external flues.

Next, the hole needs to be formed so that it is watertight and allows movement of the flue due to possible expansion and doesn't allow water to leak into the basement room.

great reply Snowhead very conclusive my gut feeling was caution the main point of your caution is the length of OUTSIDE flue a major point that could be lost by the OP internal can go a long way but external .is further regulated .cheers centralheatking

gmartine · Oct 21, 2019

...if that's the case as I've never seen such a flue perhaps a vertical flue terminal and caged somehow or with added plume extension kit?

Mexico_quest · Oct 21, 2019

snowhead said:
The flue use will have to be suitable for external use.
Not all manufacturers permit use of third party flues on their boilers.
Not all manufacturers make flues suitable for external use, other than the terminal extending from the building.

So it will be a case of finding a suitably sized boiler who's manufacturer also make /permit use of long external flues.

Next, the hole needs to be formed so that it is watertight and allows movement of the flue due to possible expansion and doesn't allow water to leak into the basement room.

Thanks all for your notes of caution, and of the probably requirement for a cage.
I'll try to find an alternative route..

EvilDrPorkChop · Oct 21, 2019

Can you not run it on the inside wall, box it in with inspection hatches and out the wall with a standard terminal?

Mexico_quest · Oct 22, 2019

EvilDrPorkChop said:
Can you not run it on the inside wall, box it in with inspection hatches and out the wall with a standard terminal?

thanks, but the underground boiler room is not underneath the rest of the house, it's right next to it. However you have a point, the current non-condensing boiler flue goes diagonally through the vertical wall which is shared by the boiler room and the side of the house at ground level, and then joins an unused ground floor fireplace.
The flue could follow the same route then go a short distance up the chimney, then exit the side of the house by making a hole in the chimney from the outside. Big job though.

Gasmk1 · Oct 22, 2019

you could do this with a vaillant as their flues ok for outside use, 15" concrete will be a tough drill you may need a specialist company also weather sealing will be a tough job as its ground level, and will get a lot of rain.

EvilDrPorkChop · Oct 22, 2019

Gasmk1 said:
you could do this with a vaillant as their flues ok for outside use, 15" concrete will be a tough drill you may need a specialist company also weather sealing will be a tough job as its ground level, and will get a lot of rain.

Are you sure about that? I was under the impression you couldn’t, and I thought gas safe said the same.

The only time you can show white on a Vaillant is when sticking out under the eaves.

Stu-B · Oct 22, 2019

You could use a Keston with twin flue, it’s only an ideal in a different jumper, the twin flue arrangement gives better length than concentric and suitable for external use.

Gasmk1 · Oct 22, 2019

yes have done it with vaillant you have to silicone the joints, may be on commercial boilers, you would need to check.

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condensing flue through cellar roof to above-ground ?

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