On 02/03/2021 23:28, Nick wrote:

Hello all,

I need to reboiler my place.
The boiler is at least 45 years old and obviously cannot last forever.
I am somewhat older and the same conditions apply.

The supply to existing boiler is 1/2" steel pipe.
I'm told that I need to have a 22mm supply for a new condensing boiler.

That may or may not be true - it depends on the power of the boiler, and
the length of the pipe run. Although beware many gas fitters seem
reluctant to actually do sums, and just go for rule of thumb answers!

(whether it is condensing or not has no bearing)

You would need to do a calculation on the size of pipe required. The
process is described in the wiy wiki, but that is offline at the moment.
However watch this space - it should be back soon.

Alternatively if you have access to BS 6891:2005 "Installation of low
pressure gas pipework of up to 35 mm (R1 1/4 in) domestic premises
(2nd family gas) €”Specification", that also describes the process.

I have put s short extract from that he

http://diyfaq.org.uk/docs/GasPipeSize.pdf

that covers the basics.

You also need to know the gas rate for the boiler - you can get that by
multiplying it power in kW by 0.09, and that will get an approximate
figure in m^3/hour.

So a 24kW boiler would be around 2.16 m^3 / hour - allow a bit for

A 15mm / 1/2" pipe can shift that within the 1mBar allowable drop for
about 5m maximum. (and that is effective length where elbows count as
0.5m of pipe, bends as 0.3m)


The routing of existing pipework cannot be followed without demolishing
about half of the interior of the house. I'm not willing to do that.

Would it be legal to run the majority of the pipework in armoured
rubber/flexible pipe?

No - although that does depend a bit on what you mean by flexible pipe.
While the normal flexible pipe used for say a cooker connection would
not be acceptable, products like Trackpipe (a stainless corrugated
plastic coated bendable gas pipe) are ok.

The last metre or two at each end would be in metal tubing. All above
ground at high level (2M) and nothing external to the house.

You can run normal copper externally, clipped to a wall. That is a
common solution to this kind of problem.



--
Cheers,

John.

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