Gas pipe sizing

[splinterdream]

Having been a service engineer for 20 years and have now started working for myself full time I need to get involved in some installs. I went to price one up today, a G/W 18HXI which has been condemned because burner seals have gone and melted everything. The gas has been fitted on 4/5 meters of 15mm from the gas meter. I told the customer this would need to be upgraded to 22mm but i dont think they believed me as G/W have been in and mentioned nothing and they want to spend very little as theyre selling up. Tried ringing G/W but couldnt get through.

Even though they admit some rads dont get up to temperature and they think the boiuler is too small (11 rads) they dont want the gas pipe altering even though i've advised this maybe the reason for poor output.

What would you do? Also does the vertical flue fit on the ultracom if anyone knows? thanks

 

[REDSAW]

what do the mi's state on pipe size?

 

[splinterdream]

Nothing Redsaw, just the usuall 'you need to get 20mbar at the boiler' stuff. On the Worceter 15ri it does say 15mm gas supply may be used as long as suffiecient gas pressure achieved.
How do you gas pipe size as a rule of thumb? At college it was a complicated diagram and equation. i've never needed to quote for myself before and with combi's it's a definate upsize but I'm not sure on the heat only's

 

[REDSAW]

Gas Pipe Sizing

 

[plumber0808]

Heat onlys will need a 22mm supply, gone are the days of 15mm gas supplies to boilers.
worcester 15kw say you can use 15mm but unless its 22 right next to it you will not get the required drop from meter to boiler.

 

[AWheating]

the gas pipe size has nowt to do with the manufacture apart from the nut and olive size at the boiler. use your ccn1 notes or corgi book and do some cals. Its the only way to get it right or put in 28mm

 

[kozak1968]

Got an android phone ? go to G.B gas pipe sizing (£4.99) Its worth it if your not to confident with the long hand method.

 

[buckley plumb]

http://www.ukcopperboard.co.uk/lite...ion-Tips/Domestic-gas-planning-and-sizing.pdf

i use this one

 

[GrahamM]

It depends on many variables if the 15mm supply will suffice, but I think any more than a few meter run it will be pushing it.
What boiler are you fitting, how many bends upto it etc.

 

[vern]

Heat onlys will need a 22mm supply, gone are the days of 15mm gas supplies to boilers.
worcester 15kw say you can use 15mm but unless its 22 right next to it you will not get the required drop from meter to boiler.

Used to be pal, 12 or 15 Ri on 15mm, 18 or 24 Ri on 22mm not any more WB have just sent out an addendum so yo can fit them all on 15 mm Subject to boiler being within 3 to 4M of gas meter and inlet pressure is per MI's, obviously common sense applies if meter is piped from 15 mm and there are gas fires, cookers it does not take away the responsibility of the GSR to do his gas calcs etc.

This is great for boilers near the meter which is 22 mm outlet with a 15 mm in the wall on a branch, we have an estate like this where I have had to run outside or hack tiles of etc, makes it much easier, plus ain't had any gas inlet problems, even on the 24 Ri

 

[Reg Man]

4m straight pipe might squeeze in your differential. So looks like 22mm pipe.

 

[splinterdream]

Thanks for all the replys, came to an arrangement with the customer and all signed on quote, if not at least 18mbar working pressure at boiler on completion, they would have to pay a fixed fee for me to come back and upgrade gas pipe at a late date.
Also downloaded Mr Combi gas sizing app, its a close call but has suggested 22mm.

 

[kirkgas]

Be careful agreeing with a customer to supply 18mb at the appliance, first of all make sure you measure the supply on the pipe NOT at the boiler gas valve so fit a test point as your last fitting, and remember that with 21mb working pressure you should have 20mb at the appliance of its under piped, only when your working pressure at the meter is 19 will you be allowed 18 at the appliance
Don't confuse the MI stating an acceptable min working pressure as it being ok to have a pipe with more than 1 mb across the carcass

 

[Reltub]

I agree with Kirk, but why can't he do a working pressure at the gas valve? I personally have never seen a pressure test point fitted on the carcass of a gas supply, or heard of any1 doing this?

 

[Reltub]

So if you cant't achieve a 1mb difference between boiler and meter at time of install you are going to isolate the boiler until you upgrade the supply?

 

[vern]

I agree with Kirk, but why can't he do a working pressure at the gas valve? I personally have never seen a pressure test point fitted on the carcass of a gas supply, or heard of any1 doing this?

On WB due to resistance of inlet pipe and valve, also suction effect on inlet test point from the fan! It will read 1 to 2 Mbar less at SIT gas valve inlet, than if you had a test point in the pipe carcass just before entry to boiler.

 

[buckley plumb]

On WB due to resistance of inlet pipe and valve, also suction effect on inlet test point from the fan! It will read 1 to 2 Mbar less at SIT gas valve inlet, than if you had a test point in the pipe carcass just before entry to boiler.

same with vaillant 1.5mb

 

[Reltub]

So what you saying, on them boilers a test point is required on the carcus?

 

[vern]

So what you saying, on them boilers a test point is required on the carcus?

No just follow the fantastic MI's on the WB it even has pictures now, and is so clear you can understand the principle without reading! Just looking at the pictures......

 

[GrahamM]

I agree with Kirk, but why can't he do a working pressure at the gas valve? I personally have never seen a pressure test point fitted on the carcass of a gas supply, or heard of any1 doing this?

As mentioned as long as you take the individual allowance for difference in supply pressure between entering the bottom of gas valve and your reading at P1 you should be ok. Worcester state a difference of 1.5mb in general.
If you want to be really thorough then pipe in a gas cock with test point bellow boiler.

So if you cant't achieve a 1mb difference between boiler and meter at time of install you are going to isolate the boiler until you upgrade the supply?

If you are fitting new boiler you should have already checked this and advised on gas pipe upgrade.
You cannot fit a new boiler if it contravenes current standards; can you?:uhoh2:

 

[Reg Man]

The best way to avoid concern, is pipe size correctly in the first place. having said that; the working pressure from end to end does not only confirm the pipe size for correctness, but also for restriction caused by debris crushing ect. So a test point just before the boiler is a consideration although not necessary; especially as VERN said WB boilers have a natural restriction through the equipment.

 

[Reltub]

If you are fitting new boiler you should have already checked this and advised on gas pipe upgrade.
You cannot fit a new boiler if it contravenes current standards; can you?:uhoh2:[/QUOTE]

Does a special force come down and physically stop you installing the boiler if it thinks you might get more than a 1mb difference?

 

[GrahamM]

If you are fitting new boiler you should have already checked this and advised on gas pipe upgrade.
You cannot fit a new boiler if it contravenes current standards; can you?:uhoh2:

Does a special force come down and physically stop you installing the boiler if it thinks you might get more than a 1mb difference?[/QUOTE]
The special force may not come down on you from above for that, but if you are ignoring the absolute basics, what else are you ignoring.

 

[Reg Man]

No half way house? Like some think.

 

[giarc00007]

g/w 18 hxi at full rate requires 2.00 m3/hr

15mm pipe at 6 metres with no elbows/bends you will get 1.9 m3/hr i would say needs upgrading to 22mm