On 26/03/2018 16:45, Harry Bloomfield wrote:
John Rumm wrote on 26/03/2018 :
I have not checked, but I would be surprised if the gas inlet is 22mm
on the boiler - so it will have to reduce somewhere!

What other appliances are fed from the same pipe run?

A 3.5Kw radiant gas fire and a gas oven/ hob, both branched directly off
the 22mm run, then the final section of pipe at 15mm feeding the boiler.
All as installed originally, except back then, the original boiler was a
32Kw unit and replaced 10 years ago with an 18kw condensing boiler,
because much less heat input was needed.

So depending on the peak demand of the cooker, you could have another
1.5m^3 per hour there. That gives just under 20m of 22mm equivalent if
you use the whole 1 mBar drop available.

(you probably need to reserve about 0.25 mBar for the 2m run of 15mm)


The installer fitting the last boiler, suggested it would need a new
pipe installed, on the surface - a long and ugly route around much of
the the outside of the house. My pipe calcs at the time suggested that
was rubbish and so it proved, because he gave in and used the existing
supply which has been absolutely fine for the past 10 years.

Now another installer is suggesting the existing may not be adequate,
from my description over the phone and is suggesting Worcester guarantee
would be invalidated if the final 15mm pipe were not upgraded. Worcester
said, if the pressure was adequate at the boiler, with all in use, then
no problem at all.

I have noted in the past that many installers seem to work to a rule of
thumb when it comes to pipe sizing rather than actually doing the sums.
So if they always suggest upgrading the pipe, then it will usually be
more than adequate without needing to think about it.

--
Cheers,

John.

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