Undersized gas pipework

[darren bastin]

Hi. I was horrified to come across an installation where two 28 combis and a 15kw cooker are fed off 22mm pipework all, the way from the meter. One of the combis and the cooker are within 3 meters of the gas meter. The other is some 35 meters away and has 22mm copper to it. Needless to say there is a problem.
My question is this . Am I correct in thinking that taking variation factors into account a domestic meter can cope with 71 kw ? and that the pressure loss if the last leg of the carcass was taken in 28 would be (effective length 39.5m ) less than 1 mb. I have to give a quote to replace the gas pipework and plan to use 35mm to the second t . Any advice would be appreciated, apologies for being a bit flakey on my maths.

 

[mutley racers]

What is the pressure at the meter when all appliances are running? If it is a u6 metre then it's max capacity is 6m3. Probably could do with a u16 in. Why are there 2 combi's in the same house

 

[Gasmk1]

if all appliances were on full rate it would need just under 243 cubic feet the u6 will probably just about do that but should really have a U16. and uprated supplies each boiler taken from the meter and also supply to cooker.

 

[ShaunCorbs]

You commercial gas reg ?

 

[darren bastin]

No I am not commercial registered. i think as a domestic gas fitter we can use 35mm, i have it in the back of my mind that purge volumes come into play. There are two combis as one does half the heating plus a cloakroom hot. The problem has not come to light as the hot water usage on the far boiler is minimal, but there is a problem.
The demand on the meter with everything running at max gas rate would be 6.6m3hr, however in practice this does not happen.The inference from one of the replies is that i would need to have the commercial ticket? if so it will save me time number crunching.

 

[darren bastin]

The working pressure remains stable at the meter at 20 mb with everything on. The fact that the far combi does not work under this scenario (on hot water, does on heating) is the issue.i

 

[ShaunCorbs]

well work out your purging volumes if over .035 you need your commercial

 

[ShaunCorbs]

The working pressure remains stable at the meter at 20 mb with everything on. The fact that the far combi does not work under this scenario (on hot water, does on heating) is the issue.i

but whats your pressure loss from the meter to the appliance ?

 

[darren bastin]

With nothing else running it 13mb at the far boiler at max rate. With everything running it goes to lock out !!

 

[ShaunCorbs]

With nothing else running it 13mb at the far boiler at max rate. With everything running it goes to lock out !!

too much max its allowed 1.5 mbar drop so 18.5mbar with everything rubbing etc

 

[darren bastin]

Yes mate. Its a mess. i am now having to do all sorts of maths just to see if I can do the job. Purge vol .03217 assuming 2m 35, 1m 0f 22m and 39.5 m of 28. just got to crunch the pressure loss now. This has turned into a revision excercise

 

[Fowlersrs]

Golden rule is much more than a metre of 35mm and your munching on commercial territory door. But calculate volume of pipework as you have done is the best way and u can see ur mighty close. Anything over 0.035m3 us commercial spec.

Your defiantly right in saying that it needs uprating, questions is will the new pipework fall into the commercial category because of its size..

 

[cdodds2004]

run a 2nd 22mm gas pipe alongside the original and tee back in by the boiler?