Gas feed to Combi

[simonbalaam]

Hello.
So now deciding we have to finally bite the bullet and replace our old boiler.
At the moment our old boiler has a 15mm gas feed. Now I know that more modern Combi Boilers need a larger bore feed. I have been told by someone (not that I think he knows) that only a certain part of the feed needs a larger bore up to the boiler and not the whole pipe from the meter. If this is true then great as ours is basically running n through the core of the house! If not then a new feed from the meter to the new boiler needs to be installed. Either way it is what it is. Just would like a heads up on what to expect.
Cheers
Simon

 

[DP]

Any boiler, not just a combi, needs the correct amount of gas to output designated power.
It is impossible to answer your question as pipe run, ( bends and bends and branches etc) power required for each appliance determines the pipe bore at different points

 

[Deleted member 267285]

As per @DP - it needs to be adequately sized - discuss this with your installer - they should be able to advise better than us.

 

[simonbalaam]

That’s fair enough. Thanks

 

[bernardgreen]

Now I know that more modern Combi Boilers need a larger bore feed.

Some modern non combi boilers may be OK with the existing 15 mm supply pipework.

 

[simonbalaam]

Some modern non combi boilers may be OK with the existing 15 mm supply pipework.

Yeah we will be probably replacing Combi with Combi.

 

[Harry Bloomfield]

Probably best to start by working out the route of your existing pipework, the sizes, where it changes size, and the bends. Then insist anyone quoting for the work, does the pipe size calcs, and produce a copy for you to see they have done the calcs. Many installers may not want to be bothered, but will err on the side of fitting new, larger pipe work.

 

[DP]

At the moment our old boiler has a 15mm gas feed

Is present boiler a combi?
15mm pipe would seem undersized unless boiler is close to the gas meter

 

[simonbalaam]

Is present boiler a combi?
15mm pipe would seem undersized unless boiler is close to the gas meter

Currently have a Baxi 133 HE plus. Would like something with similar specs.
Only Gas appliance in the house is the boiler and it’s no where near meter as it’s in the loft!!

 

[Deleted member 294929]

I'm a bit lazy when it comes to this so I generally run a 28mm at least to the tee for cooker and boiler.

 

[ianmcd]

testing working pressure gas boiler - Google Search

 

[bernardgreen]

similar to when you turn a water tap on....

There are significant differences between a gas supply and a water supply.

The first one is that gas is compressible and water is not compressible.

The gas main feeds a pressure regulator which feeds the meter, hence the pressure of gas in the house at the meter is fixed by the setting on the pressure regulator. The amount of gas being used does not ( normally ) affect the pressure of the gas at the meter as the regulator will control the pressure by altering it's valve according to gas flow required.

 

[dilalio]

But pressure needs to be measured with all appliances on full load

No it doesn't!

 

[DP]

See #6

Perphaps you need to read #9
Gas meter is ‘miles’ away. 15mm would suggest a heat only boiler. Not the first time a poster has confused a heat only boiler for a combi and called the cylinder a boiler

 

[old duffer]

Its a simple maths calculation which is created using set values for each bend and pipe run and take-off.
This will help you https://www.gb-gas.co.uk/clc/pipesize/GasPipeCalculator.htm