Gas boiler pipe size - old 15mm, new 22mm!...

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I have an old potterton wall hung boiler which has a gas pipe connection in 15mm diameter (copper).

I am thinking of upgrading to a new boiler but all new boilers seem to have a 22mm connection for the gas supply.

Does this mean the whole gas pipe from the branch conenction will have to be upsized to 22mm or can the pipe near the boiler have a reducer, 22-15mm. The meter is literally 1-1.5 metres from the boiler, we also have a gas fire which is about 2-3 meters from the gas meter.

The pipe from the meter is in steel (low carbon...) and the pipe to the boiler is in copper so it must tee off under the floor.
 
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The gas pipe size is determined by the gas requirements of the boiler.

Any gas registered engineer will know how to calculate the required gas pipe size.

The gas pipe size involves the entire run between the meter and the boiler.

It sounds as if you are contemplating an unregistered installer?

Tony
 
Hi

I am thinking of hanging the jig/connecting the flue and piping up myself and getting it commissioned by a gas safe engineer as by law.

i believe gas pipe sizing is done in sections, eg from meter to 1st tee and then from tee to boiler, so 2 sections in my case.
 
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Hi

I am thinking of hanging the jig/connecting the flue and piping up myself and getting it commissioned by a gas safe engineer as by law.

i believe gas pipe sizing is done in sections, eg from meter to 1st tee and then from tee to boiler, so 2 sections in my case.

you don't even know how to size the pipework and your gonna pipe it up yourself

good luck if you can find an rgi to commission it :eek:
 
i was just querying. i know there should be a 1mbar pressure drop MAX from meter outlet to appliance inlet. but as old boiler was in 15mm and working fine for years just qondered if i needed to re-pipe all from meter or just from tee or just at boiler connection point.
 
..I am thinking of upgrading to a new boiler but all new boilers seem to have a 22mm connection for the gas supply.

Does this mean the whole gas pipe from the branch conenction will have to be upsized to 22mm or can the pipe near the boiler have a reducer, 22-15mm. The meter is literally 1-1.5 metres from the boiler, we also have a gas fire which is about 2-3 meters from the gas meter....

Most of mine get 28 mm, but as yours is really close to the meter, 22 would suffice.
 
Hi

I am thinking of hanging the jig/connecting the flue and piping up myself and getting it commissioned by a gas safe engineer as by law.

i believe gas pipe sizing is done in sections, eg from meter to 1st tee and then from tee to boiler, so 2 sections in my case.

You obviously dont understand the requirements!

Fitting the hanging bracket, fitting the flue and certainly fitting any gas pipes all have to be done by an RGI !

The gas sizing has to be done taking into account all appliances using gas and the relative lengths of pipework.

I dont encourage unregistered gas installation work so I am not going to tell you how to calculate the sizes but its in the textbooks.

One of the forum idiots will be posting shortly to say that there is nothing illegal about calculating gas pipe sizes!

Tony
 
i might just get a gas safe reg installer in to do it now as he's gonna be in to do all the tightness testing before and comissioning it after as well.

would the boiler need 22mm from the tee (which is from the meter and goes off to the fire and boiler) or just close to appliance, ie 22mm/15mm reducer?
 
See the MI's. Some state that you must not fit the gas tail to a pipe of lesser diameter.

MI's over rule any regs.
 
i was just querying. i know there should be a 1mbar pressure drop MAX from meter outlet to appliance inlet. but as old boiler was in 15mm and working fine for years just qondered if i needed to re-pipe all from meter or just from tee or just at boiler connection point.
You shouldn't repipe anything to do with the gas.
How do you know it was working fine?
I was called out to a boiler last week that was working "fine" on a 15 mm pipe according to the owner.
It worked, but not when I left. The burner pressure was 2 mbar, in stead of the recommended 12.
The boiler was installed by a cowboy, subsequently neglected, and lethally dangerous.
Condemned, disconnected, and gas capped off.
But it worked "fine".
 
So the gas pressure was too low due to a partially/blocked injector or undersized/blocked supply pipe...?

I'd never do gas work DIY. it is not worth it.
 
...One of the forum idiots will be posting shortly to say that there is nothing illegal about calculating gas pipe sizes!

Tony
Never thought of myself as the forum-idiot, nor as the village-idiot for that matter, but I do disagree that it is illegal for a diy-er to calculate gaspipe sizes.

I doubt that the calculation will be correct in more than about 1% of cases, but that doesn't make it illegal. If the calculation was wrong, it could of course be illegal to then install the wrong pipe.
 
To calculate gas pipe size, you need to multply each length (including fitting resistances etc) by the maximum number of sections on that pipework. This ensure when all appliances are on at the same time, no more than 1mbar drop is at each appliance from the meter outlet to the appliance inlet.

Eg/ meter to tee, to boiler (2 sections)

meter to tee to fire 2 sections

meter to cooker via 2 tees - 3 sections


if the boiler was say 2 metres from the meter with 1 tee and 1 elbow, this would equate to 3 metres of equivalne tlength. multiply by 3 (3 sections maximum in installation) = 9 metres. You then need to know the gas rate for the boiler and from a chart work out which pipe size is require d (always go to the next size up)..

each section needs to be caulcated though, starting from the meter downstream.

Best to leave it to a reg installer though and then you have no worries.
 
To calculate gas pipe size, you need to multply each length (including fitting resistances etc) by the maximum number of sections on that pipework.
Not quite; 3 fires, 1 cooker and 1 boiler would mean times 5.
What sort of pipe would that give for a 37 kW boiler at 15 metres from the meter with 9 elbows, about 70 mm? :eek:
 

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