Gas pipe

[PM]

I want to extend a gas pipe, the existing pipe is 15mm but the length of the new pipe is such that I will need to use 22mm pipe for the extension.

Will it cause a problem if the gas travels through the 15mm pipe first then into the 22mm pipe via a reducing coupler, or should the whole length be

22mm? The present length of pipe is approx 3m (including adjustment for bends and elbows), the extended length is approx 12m.

There will only be one appliance served.

Thanks

Pete

[Lobster]

Which is what, exactly? If it's a hungry combi, it will need 22mm all the way from the meter.

David

[John Rumm]

While that may well turn out to be true, it would probably be better to do the sums and see what it actually does require. Much depends on the flow rate requirement of the appliance in question.

Data tables here:

[Lobster]

That's what I meant actually - I didn't mean that if it was a combi it would *by definition* need the 22mm pipe!

David

[tarquinlinbin]

You cant fit a 10 gallon hat on a two pint head...now which song is that from? Is it Johnny Cash?

Remove antispam and add 670 after bra to email

[PM]

It will be a condensing non-combi boiler, don't know which one yet.

In general, assuming that I can use 3m of 15mm and 9m of 22mm, can I do what I want to do?

[Antony]

The pipe causes a pressure drop depending on it's size, length, number of bends and the rate of flow. Use the CDA doc that John linked to to do the proper calculations - don't make assumptions. The problem you're likely to have with a small pipe and the start of the run, is that is where the highest flow rate is (i.e. before it branches off to the cooker, fire, boiler), so you'll get a very high pressure drop. Current regs only allow a 1mbar drop at any appliance when all appliances are running at maximum power, which is very hard to achieve without 22 or

28mm pipe (except on very short runs).

-Antony

[PM]

I realise all that, and have used a similar calculator to work out that I need to run at least some of the pipe in 22mm. Bearing in mind I am running just one appliance, there is only one gas supply rate requirement over the whole length of the pipe.

Perhaps a better way of phrasing my question is:

When a single run of gas pipe with no tees is partly 15mm and partly 22mm, does it make any difference if the run is gas meter to 15mm pipe to 22mm pipe to appliance, or gas meter to 22mm pipe to 15mm pipe to appliance?

Thanks Pete

[John Stumbles]

No: it's like resistances in series (if you're familiar with basic electrics). The overall resistance will be the same whichever order your 2 individual resistors are connected in.

Aesthetically, however, it stinks :-)

[John Rumm]

Don't think it makes any difference... it is the overall flow resistance that counts, the sequence of where the restrictions are does not matter.

(otherwise an elbow at the start of a pipe run would have to count differently than one at the end)

[PM]

Aesthetics isn't an issue, all the 15mm pipe is buried in concrete and the

22mm will be mostly under the upstairs floor with the exception of a floor to ceiling length which will be in a cupboard.

Thanks for the answer

Pete

[PM]

That ties in with what I thought, having read that the restriction is down to friction between the gas and the wall of the pipe. I thought it best to be sure though.

Thanks for the answer

Pete