Iron gas pipe

[DursleyDonkey]

I'm changing my boiler for a high power combi (37 kW). The house is about 35 years old and the gas is in an iron pipe under the floor screed. The pipe is about 6 m long and about the same diameter as 22 mm copper (I think that's 3/4"). The plumber says he'll have to test it for leaks - if it's sound he can re-use it, but it will eventually need replacing.

My question is how long would you expect a pipe of this nature to last - should I replace it now or could it have many years of useful life left in it? Would it be able to run such a big boiler.

 

[JohnD]

if the external size is 3/4", then the internal size is 1/2", which is like 15mm copper.

it is too small for a large boiler, although you may get away with it if it is a short branch from a larger pipe. 37kW is large.

additionally, if the pipe is iron, it might be old, and have rust and dust inside it

be prepared, you will probably need a new pipe from the meter.

 

[DursleyDonkey]

Thanks John. Is 35 years old for a gas pipe? Can you test the capacity before the work is started, or do you just wait till the job is done and find it doesn't work?

 

[JohnD]

the clever guys can work out the size required by the length of the pipe, the number of elbows, and the demand of the boiler.

With luck one of them will be along soon.

How far is the boiler from the meter?

I expect your installer will work it out and insist on changing it to a size that works.

 

[spacethegas]

How far is the boiler from the meter?

thats the question.

 

[DursleyDonkey]

The iron pipe is about 6 m to where it would join on. Then we're going to need another 5-6 m of copper to the boiler.

 

[spacethegas]

then the iron pipework is redundant.

 

[DursleyDonkey]

then the iron pipework is redundant.

Sorry, not sure what you mean by "redundant". Are you saying we shouldn't reuse it, or are you saying it won't matter?

 

[Softus]

the clever guys can work out the size required by the length of the pipe, the number of elbows, and the demand of the boiler.

Clever?

That would appear to be disingenuous.

 

[spacethegas]

the iron pipework cannot be used as part of the supply to the boiler.

 

[JohnD]

correction

the non-disingenuous guys who know about out gas volumes and pipe resistance (i.e. not me) can work out what diameter pipe you need, knowing the boiler, length of run, and number of elbows.

 

[Softus]

the non-disingenuous guys who know about out gas volumes and pipe resistance (i.e. not me) can work out what diameter pipe you need, knowing the boiler, length of run, and number of elbows.

Anyone could work it out, whether or not they're sincere, and whether or not they're clever. However, it would be unwise for a non-RGI to give that advice on the forum.

I don't think you had a good motive for calling RGIs clever.

 

[JohnD]

put that goad away.

 

[Softus]

I don't think you had a good word for using a motive that will be unfamiliar to a substantial proportion of readers.

 

[Paul Barker]

nothing wrong with material or longevity not a hope in hell of ensuring the minimum 1 mbar drop across pipework to your prospective boiler. You need some 28mm pipe and very little 22mm pipe. Or get a storage combi or something cobbled together of your own like a low output combi and a small unvented cylinder organised by someone more clever. For instance a person capable of pipesizing should work it out.