Gas pipe size

[beseeinyou]

Hi,

Anyone help with this?, I am in a 22 yr old house and am currently obtaining quotes to change my existing regular boiler / cylinder / loft tank arrangement to a Worcester Bosch combi system, above the utility room where it is sited there is a loft area where you can see the gas pipe and heating pipes, the gas pipe coming from the meter is a steel pipe which is then jointed to a 15mm copper pipe in this loft space and the 15mm copper then goes to the boiler, I've attached a link to a photo of it which hopefully works:

https://photos.app.goo.gl/ap35NEHT4hjri8c4A

First guy says the steel pipe is 22mm and they only have to fit a new 22mm copper up to the steel pipe, second guy says that the steel pipe although looking bigger is actually a steel 15mm pipe and that this can't be used and a completely new 22mm pipe has to be installed from the meter to the boiler which is a real hassle due to the location of the meter being at the completely opposite end of the house to the boiler.

Anyone know about this at all?

Beseeinyou

[jfgw]

Comparing the sizes of the copper and the steel pipes in your photograph, I determined that the steel pipe is approximately 21.6mm outside diameter. 1/2" steel pipe is 21.3mm outside diameter which is, to within the accuracy of my measuring, the same.

Your steel pipe is 1/2" or "DN15" so, regrettably, the second guy is correct.


Julian F. G. W.

[dspp]

Comparing the sizes of the copper and the steel pipes in your photograph, I determined that the steel pipe is approximately 21.6mm outside diameter. 1/2" steel pipe is 21.3mm outside diameter which is, to within the accuracy of my measuring, the same.

Your steel pipe is 1/2" or "DN15" so, regrettably, the second guy is correct.


Julian F. G. W.

But what's the ID, and for that matter the pressure rating ?

- dspp

[88V8]

What size is the boiler?
We ran a 80000 bthu off a half inch pipe. Plus a four-burner gas hob.

V8

[jfgw]

But what's the ID, and for that matter the pressure rating ?

The ID of half inch steel pipe is about 16mm.
15mm copper tube is 13.6mm ID.
22mm copper tube is 20.2mm ID.

I'm not sure of the pressure rating without looking it up but it will be a few hundred times that of the gas.

Julian F. G. W.

[dspp]

But what's the ID, and for that matter the pressure rating ?

The ID of half inch steel pipe is about 16mm.
15mm copper tube is 13.6mm ID.
22mm copper tube is 20.2mm ID.

I'm not sure of the pressure rating without looking it up but it will be a few hundred times that of the gas.

Julian F. G. W.

Thank you JFGW.

It seems to me that what the second guy is trying to talk about is the steel pipe's ID, as that is what determines the pressure drop and flow rate, but the message got somewhat scrambled either in his brain or in the recounting.

I am not a plumber, so I don't know what regulatory norms they have to work to, but I have designed somewhat larger gas pipes in my time. My opinion is that for domestic pressures & flow rates either solution is going to be sufficient from a narrow technical perspective. However the plumbers need to work to their regulations and so my advice would be to get both to quote you, including fully signing off the job and providing you with the correct paperwork. To do this they will need to be registered on the Gas Safe Register:

https://www.gassaferegister.co.uk/find-an-engineer/
http://www.hse.gov.uk/gas/landlords/saf ... whocan.htm

I am very happy to defer to a plumber regarding UK norms ........

regards, dspp

[jfgw]

I am not a gas fitter but understand that a maximum pressure drop of 1mbar is allowed. Combi boilers are much more powerful than most non-combi boilers so use gas at a higher rate. The OP mentions a long pipe run so I would be very surprised if the existing pipe is sufficient. Galvanised pipe shouldn't be bent so there may be a few elbows, although swept bends are available which cause less pressure drop.

Julian F. G. W.

[beseeinyou]

"What size is the boiler?"

The boiler is either a Greenstar 38CDi Classic or Greenstar 42CDi Classic, not too sure what you mean by size exactly, it is stated as 30KW ?

Both surveyors are from Worcester's accredited installers list, as will the others who have still to look at it, so no concerns about Gas Safe register etc.

Worcester's installation guide states "Under no circumstance should the size of the gas supply pipe be less than 22 mm" so I guess the only question would be is if that steel pipe qualifies, so far one guy thinks it does and one guy doesn't, next guy is due this afternoon.

That's interesting too Julian about maximum pressure drop, again Worcester's installation guide states "The pressure at the boiler must not be less than the pressure read at the meter minus 1 mbar", I fished out my last service sheet and the guy recorded 23mBar at the meter and 19.5mBar at the boiler, a drop of 3.5mBar, so clearly that won't satisfy Worcester's requirements, it looks very much that a new pipe will have to be installed as I'm thinking I wouldn't have much faith now in just hooking it up to the existing steel pipe.

Beseeinyou

[88V8]

"What size is the boiler?"

The boiler is either a Greenstar 38CDi Classic or Greenstar 42CDi Classic, not too sure what you mean by size exactly, it is stated as 30KW ?

100,000 bthu.
Quite big. Way bigger than we needed for our 1850 sq ft house.

Dunno what this is costing, but it you're only changing a (working) system for reasons of economy, as this is a Financial site I'll mention that you should factor in the cost x 5.5% which is the current yield on Prefs, and minus that off the alleged annual savings.
There's a lot to be said, imho, for a simple old boiler not saddled with a complexified collection of electronics.

V8

[beseeinyou]

3rd guy out this afternoon and as soon as he looked at the steel pipe he declared it as the steel equivalent of 15mm copper and that it could not be used.

Beseeinyou

[jfgw]

I fished out my last service sheet and the guy recorded 23mBar at the meter and 19.5mBar at the boiler, a drop of 3.5mBar...

That's a big drop. What power is the boiler?

Julian F. G. W.

[Mike4]

Julian is correct, a maximum pressure drop between meter outlet and boiler inlet of 1.0mbar is permissible.

Sadly achieving this usually requires gas pipes the diameter of drain pipes so few plumbers bother getting it dead right, preferring to insist on 22mm copper pipe all the way from the meter to the boiler then blaming unknown factors when the pressure drop is still 2 or 3 mbar.

There are sizing charts we use for working out the diameter of copper tube needed based on length from meter to appliance and number of bends etc. but even these give unpredictable results in my experience.

Using the 1/2" steel pipe (21mm external diameter approx) will probably result in massive pressure drop completely unacceptable to GSR so I'd go with one of the bods advising replacing it. If once done you invite GSR to come and do a safety check on your installation, this is one of the tests they will carry out. If they find a pressure drop of more than 1.0mbar they will issue you with a Warning Notice not to use the installation until rectified.

These pressure drop charts can be easily found on the net so you can have a bash at doing your own calcs and see if 22mm ought to be big enough, or if you need to go to 28mm or even bigger.

The boiler you are removing will undoubtedly be far lower in gas demand that the new one you are planning so the existing gas supply is highly unlikely to be adequate.

[beseeinyou]

The existing boiler is a Glowworm Ultimate 80FF which I believe is about 23 / 24 KW ?

Both guys spoke about the new pipe possibly being 28mm so far then dropping to 22mm but they would calculate it in advance if they are awarded the work.

I have it in my mind now that using the existing pipe is not going to happen and I wouldn't have any faith in the company who's surveyor didn't know that, another company coming out on Monday and I hope to get one more to quote too, four other companies so far haven't phoned back.

Beseeinyou

[Mike4]

The existing boiler is a Glowworm Ultimate 80FF which I believe is about 23 / 24 KW ?

Both guys spoke about the new pipe possibly being 28mm so far then dropping to 22mm but they would calculate it in advance if they are awarded the work.

I have it in my mind now that using the existing pipe is not going to happen and I wouldn't have any faith in the company who's surveyor didn't know that, another company coming out on Monday and I hope to get one more to quote too, four other companies so far haven't phoned back.

Beseeinyou

So your 38 or 42 kW Worcester is way bigger!

Yes 28mm most of the way then final connection in 22 sounds probable.

The four who haven't called back might simply be too busy. No excuse but that is what happens when its a solo gas bod and there is no office staff. At some point in the day one has to get off the fone and actually go out and get some work done!

Or maybe they don't like installing Worcesters. Some gas bods love them, others refuse to have anything to do with them. Marmite boilers.