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Pipe size to combi boiler question

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Discuss Pipe size to combi boiler question in the Boilers area at Plumbers Forums

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Steelej

Hi Guys,I recently had british gas out to my flat to look at fitting a new combi boiler, they've come back to me today and say they can't do a combi becuase i have a 22mm pipe from my meter and new building regulations say that it should be 28mm. My flat is on the 2nd floor of our building and the meters are at ground level all together for all the flats in my little block.I've also had a quote from N-power who say this won't be a problem and the 22mm pipe will be just fine and they can fit a combi no problem, so the question, who's right?Thanks for any info.John.
 
It depends on the length of the run and how many bends and elbows
 
They simply said it was building regulations, inititally the engineer thought it would be fine but then said on checking they couldn't do it. They didn't check any pressure etc they just said it had to be 28mm from the meter. My neighbour has a 28kw combi boiler working fine using the 22mm pipework from the meter which is located in the same place as mine.Has anyone heard of this though, that building regs state it must be 28mm?John.
 
Not sure of the building regs but the pipe must be big enough to supply gas to the appliance with a maximum pressure drop between the meter & appliance of 1mbar with the appliance running at full pelt. Give it a few hours and some of the more experienced lads on here will probably give you the exact info re. building regs
 
Steelej said:
They simply said it was building regulations, inititally the engineer thought it would be fine but then said on checking they couldn't do it. They didn't check any pressure etc they just said it had to be 28mm from the meter. My neighbour has a 28kw combi boiler working fine using the 22mm pipework from the meter which is located in the same place as mine.Has anyone heard of this though, that building regs state it must be 28mm?John.
Click to expand...

with all due respect you dont KNOW your neighbours boiler is working fine, if the gas pipe is too small and or too long it will not operate at maximum performance but the way your neighbours uses the boiler may be masking this, give us a quick measure of the run including number of bends he has and we can calculate whether the gas pipe is right or not
 
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kirkgas said:
with all due respect you dont KNOW your neighbours boiler is working fine, if the gas pipe is too small and or too long it will not operate at maximum performance but the way your neighbours uses the boiler may be masking this, give us a quick measure of the run including number of bends he has and we can calculate whether the gas pipe is right or not
Click to expand...
You're absolutely right i don't know that it's working fine, but from his information it heats his flat, costs him less than his old boiler and gives him all the hot water that he needs which is all i'm looking for in a boiler. I'm not a heating engineer and there's no way for me to give the info required on the pipework, it's all completely hidden, but the meter is 2 floors below where my flat is located so probably somewhere in the region of 15-20 metres from my flat.Thanks for the responses so far.John.
 
Kirkgas, i see you're in Coatbridge, are you a gas installer? If so do you fancy coming to my flat to give me a quote as i'm in Glasgow? :)John.
 
when you consider that the tappings that come off a regular meter are in 22mm pipe it would defeat the purpose piping from the meter defeats the purpose unless you up grade the meter.
 
i can pritty much guarntee 22mm is adequate for most combi's espically for a flat as you would need no more than a 30kw and that would be a over kill, how far away is the meter? 28mm on a 22mm connection isnt great anyways, my college tutor told me to tee into 2x22mm feeds then back to one is better for long distance runs as you get a better volume of gas, although i have never ran 2x22mm
 
mrplumberman said:
when you consider that the tappings that come off a regular meter are in 22mm pipe it would defeat the purpose piping from the meter defeats the purpose unless you up grade the meter.
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You're wrong. Upgrading to 28mm after the meter will make a difference.
 
as previously stated the pipe size should be ascertained by calculation, the name of the formula escapes me at the mo but most gas techs will use tables anyhow. I don't know where or even if gas pipe sizing is detailed in the building regs, if you could get a citation from them I'd genuinely like to know
 
I'm in Glasgow I can give you a quote if you want to arrange a time, I'm quite busy though at the moment

what type of boiler do you have at the moment ? and how old ?
 
Steelej said:
You're absolutely right i don't know that it's working fine, but from his information it heats his flat, costs him less than his old boiler and gives him all the hot water that he needs which is all i'm looking for in a boiler. I'm not a heating engineer and there's no way for me to give the info required on the pipework, it's all completely hidden, but the meter is 2 floors below where my flat is located so probably somewhere in the region of 15-20 metres from my flat.Thanks for the responses so far.John.
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If you are talking in region of 20 meters as you estimate above then the BG engineer sounds like he is on the ball. By my reckoning that would be right on the limit to provide the gas for your average boiler. You have not mentioned any other gas appliance, which would increase the gas demand even more, reducing the max length of pipe run further. British Gas will not knock back a potential sale without good reason. Trust me on that. I would be inclined to listen to their advice on this. There is always a first. :smiley2:
cdodds2004 said:
i can pritty much guarntee 22mm is adequate for most combi's espically for a flat as you would need no more than a 30kw and that would be a over kill, how far away is the meter? 28mm on a 22mm connection isnt great anyways, my college tutor told me to tee into 2x22mm feeds then back to one is better for long distance runs as you get a better volume of gas, although i have never ran 2x22mm
Click to expand...
You can't guarantee anything without actually sizing up the pipe runs and demand.
 
24kw boiler, 20metres 22mm tube and 5 bends with no further appliances has a 0.75mb drop which is less than the 1mb limit
 
Steelej said:
Kirkgas, i see you're in Coatbridge, are you a gas installer? If so do you fancy coming to my flat to give me a quote as i'm in Glasgow? :)John.
Click to expand...

haha i'm not a real worker anymore, i just teach it for a living, far easier to talk about it rather than do it, send me a PM with an email address and i might be able to get someone to look at it for you
 
Steelej said:
You're absolutely right i don't know that it's working fine, but from his information it heats his flat, costs him less than his old boiler and gives him all the hot water that he needs which is all i'm looking for in a boiler. I'm not a heating engineer and there's no way for me to give the info required on the pipework, it's all completely hidden, but the meter is 2 floors below where my flat is located so probably somewhere in the region of 15-20 metres from my flat.Thanks for the responses so far.John.
Click to expand...

i wasnt having a dig that you didnt know, merely stating that the neighbours use of the boiler may mask the gas pipe being too small/far from the meter, but if you fit yours the same way your use might show up the deficiences and you will be disapointed
 
stani said:
24kw boiler, 20metres 22mm tube and 5 bends with no further appliances has a 0.75mb drop which is less than the 1mb limit
Click to expand...

you can run a 24kw boiler on a 30m equivelent pipe run (actual pipe length + 0.5m per bend)
 
kirkgas said:
you can run a 24kw boiler on a 30m equivelent pipe run (actual pipe length + 0.5m per bend)
Click to expand...

yea realised that , its just to give an idea of a boiler size and length of pipe for a small flat,
 
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