Gas supply.

[Dave Plowman (News]

Mate has an 1980s terraced 2 bed small house. Still on the original non room sealed boiler. Stored HW. Originally all cooking by gas - now just a gas hob.

Intends having the boiler changed to a combi. 30Kw by the spec. BG says they need to run in a new gas main. The original buried in the concrete base - so will be run surface inside up to the roof void, then surface down to the new boiler.

BG didn't do a flow test before specifying the new feed. Other thing is pal is considering a loft conversion.

Any comments?

[Andy Burns]

I think they always say that, tried it on Dad, except he used to be gas board district supervisor, told them to show him the calcs to demonstrate it needed

22mm, they did them and suddenly the original 15mm pipe was deemed ok ...

[Harry Bloomfield, Esq.]

Dave Plowman (News) laid this down on his screen :

Combi boilers need much more gas to heat the water from cold, than stored water boilers, so often the pipe size will need to be increased. Having said that, boiler installers do often suggest the pipe is too small even when it is not - Our last but one boiler swap, the installer wanted to fit a combi, which I didn't want, and to install a new larger pipe right round the outside of the house. Even when it was made clear that he wasn't going to be fitting a combi, he was still insisting the pipe was too small. I had done the calcs it was fine, so I asked him to actually do the calcs - they proved the pipe was adequate.

The existing pipe was 22mm all the way, apart from the final 1m, feeding gas fire in the middle, hob and double gas oven. Tests once completed, confirmed the calcs.

Ask the engineer to show you his calcs..

[Andy Burns]

this was for a system boiler, not a combi.

[Fredxx]

I read somewhere that Gas Safe instruct their fitters to use 22mm on Combis, they seemingly have little or no confidence on their members can do the calcs. Many boiler have the inlet sized at 22mm too as is my system boiler.

[Tricky Dicky]

When you say gas main surely you not referring to the pipe coming into the meter? These are must be about 40mm already. Any meter I have come across has had a 22mm outlet. If it is the pipe from the meter then I know most boiler manufacturers recommend a 22mm feed to the boiler, but this sounds to me like they simply want to take the simplest route convenient for them.

Our bungalow originally had a back boiler in the lounge which had a 22mm feed routed under the floor reducing to 15mm for the last metre. When the previous owner installed a combi in the airing cupboard the fitter capped off the original pipe work and left it in situ. The new feed was installed as in your case with the feed running up inside a pantry across the loft down into the airing cupboard. The only advantage I can see to that route was there was no necessity to lift any floorboards. Not that it required much of that anyway as the airing cupboard sits along side the back boiler opening. When we did the kitchen and demolished the pantry that left an unsightly pipe that would have come through a worktop. I had a gas fitter remove that pipe, reuse the original pipe work passing 22mm through the wall all the way to the boiler. Mind you I already had floorboards up for electrical work and had made an opening in the wall so he was happy to piece in the necessary pipe work.

Richard

[Dave Plowman (News]

I've not been round to look, but mate says the pipes from the meter (inside the house) appears to be the same iron barrel in and out. And it's a small house. I can't see any reason why the pipe from the meter doesn't run direct to the kitchen. So perhaps fewer bends than you'd get in many installations.

Rather than calcs, which might be difficult if you can't see the buried pipe run, is there not a meter that can measure the flow to see if it's adequate?

[Harry Bloomfield, Esq.]

Fredxx pretended :

There is an online calc somewhere around, makes it easy.

[Tim+]

Whilst flow is what you?re trying to guarantee doesn?t a measure of pressure at the boiler whilst all gas appliances are on tell you enough (in theory)? If the required inlet pressure is maintained under those circumstance one can infer the the flow must be adequate surely?

Tim

[Dave Plowman (News]

I dunno, Tim.

It just seemed odd to me 'they' decided a new supply was needed without doing any tests.

My mate has the same hate as me for surface run services. Apart from the extra costs.