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QUESTION:I am contemplating the inevitable replacement of my boiler with a
new condensing one (not combi).
I guess the flue could be a problem, as it would have to be on a
gable end, which is only 1m from the boundary with my neighbour.
I presume the flue would have to be extended up above roof
height. This sounds expensive, if it can be done at all.
Has anybody else dealt with this?
ANSWER: It depends on the make of the boiler. Flue systems for some,
especially the concentric types, are proprietary and can become
expensive if you need any substantial length of them.
However, there are makes such as Keston which have a flue system based
on 50mm high temperature plastic waste pipe. The boiler comes with
the terminal fittings for the end and then you buy the pipework and
other fittings pretty cheaply from a plumber's merchant like
Plumbcenter or a host of others.
Other boilers may have adaptors as an option that can be fitted to the
boiler instead of the regular flue system to convert to a twin 50mm
tube arrangement. I have a MAN Micromat which has that as an
optional component.
There is enormous flexibility, based on a few rules about the running
of such a flue system - it can be inside or outside the house and can
run a considerable distance. You don't necessarily even have to run
the pipes in parallel to a common point since this boiler type is fan
operated anyway.
There are regulations around the siting of flues and you can find
useful information if you download boiler installation instructions.
Taking Keston again as an example, they have downloadable PDFs for all
of their boilers. There are generic rules and then manufacturers may
have additions and alternatives which take precedence.
Another alternative is to have a dual or concentric flue running up
inside the house and then through the roof. There are special
sealing adaptors which replace a tile to do this.
Generally you will find that manufacturer's technical departments are
really helpful with advice. It can be useful to make a reasonably
dimensioned set of sketches of the property and the environment to
help with this.
Even if you do comply with the regulations, it is neighbourly to
direct the flue up and away from their property if you can. As you
probably know, condensing boilers do produce a plume of water vapour
under certain operating conditions although this is not as big a deal
as some people would suggest. You can use 135 degree elbows in the
pipework to direct the output where you want.
Don't forget that you also need to take account of disposing of the
condensate. Since this is mildly acidic, it needs to be piped away
from the boiler in plastic pipe (overflow is commonly used) and led to
a drain outside the property. Alternatively it can be run into an
existing waste system via a trap.
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