28mm gas fitting for combi??

[Doug99]

I have been advised that new condensor boilers require a 28mm gas feed. My installer has said that he intends to increase the current 22mm pipework from the meter in the garage to 28mm but the pipework from the garage to the boiler (under floorboards to the airing cupbard are 22mm). Will this be a waste of time if a 22mm section remains in place?

Surely the gas flow rate is limited by the narrowest diameter within the gas feed.

 

[JPC]

its common to start a gas run in 28mm now and at a point reduce it to 22. this will feed more gas to the appliance. it also compensates for elbows.

there are calculations for all this. it determines the gas requirements.

i'm not corgi, so cant be too technical, but it sounds right and i have done/seen done runs like this (when in company with my corgi mate(for all the eye brow raisers))

 

[ollski]

no it don't work like that its the overall resistance of the pipe measured on the length and fittings to supply a give volume of gas. There is a calculation mehod I guess might be floating on the net somewhere.

 

[ChrisR]

QUIte often there's a nasty old iron gas pipe buried in concrete which we're obliged to use because of the cost of replacing it. They can be pretty resistive so can mean that all the rest of the pipe has to be 28, which is fine. We'll be using 35mm on domestic soon - bring it on!

 

[Paul Barker]

What's that Chris we going to be let loose on bigger pipes?

 

[cowboyplumber]

Who's using 'proper' 28 meter unions, and who's using inverted 28-22 reducers? anyone noticed any difference using either?

 

[ChrisR]

Yes Paul my corgi inspector was on about it, and I saw a reference on the ARGI site. Will be useful for all those 70kW combis?

Yes CC I have used 1" to 28mm connectors on a meter (lucky, cos so may have 3/4" outlets). Had to break the law though - cut the slot bigger on the meter mounting plate to get the thing in. (After that I had 2 x 28mm feeds to 2 combis, each with their input iso valves replaced with full flow ones, and slow bends only. Theoretical pressure drop 1 mbar, actual 2mbar, and the meter dropped 2mbar on full flow. OK overall as the regulator was set to 23mbar (how DO you think it got to 23mbar??))