Gas supply size help

[Gasguru]

However, I can't see why a modern equivalent of the 20-30 would require a larger supply if they are meant to be more efficient.

Because the majority of existing gas pipework I see is undersized. The majority of boiler installations did not (and often still don't) comply with the regulations.

So even your existing boiler may be installed on undersized pipework; if the boiler gas valve has a test point this can be verified.

When I installed boilers if the pipework looked marginal I would install the new boiler and then check the pressure drop....if too great then I would then upgrade the pipe. You just make sure the customer understands this from the outset. Cowboy installers keep this quiet since it allows them to undercut the competition despite being illegal. The boiler may then appear to funtion correctly to the homeowner despite possible safety implications.

The gas pressure from the meter is approximately 100 times LOWER than a car tyre pressure, therefore friction within the pipe and fittings will cause a significant pressure drop if the pipework is not adequately sized. 35mm pipe is approved for domestic work and is sometimes necessary.

 

[fender]

Many thanks,

It now begins to make sense...

 

[Nixt]

Very helpful comment mate, thanks.....

I'm just interested, is that ok? - that's how you learn.

I can now see why a combi would require a larger supply, that was explained quite well. However, I can't see why a modern equivalent of the 20-30 would require a larger supply if they are meant to be more efficient.

Are you sure you just want to learn and it has nothing to do with that nasty con-merchant of an installer trying to extract your hard earned? Because you're repeating the same question that has been answered. As mentioned before you are assuming the existing installation is correct. Proving him right or wrong is going to cost, whichever way no-one can provide you with a inlet pressure test over the web to save this expense for you. Sorry I forgot it's nothing to do with that you're just here to learn.

 

[Nixt]

Sorry OP, you seem to have grasped it now so I take back my last post.

 

[fender]

Very helpful comment mate, thanks.....

I'm just interested, is that ok? - that's how you learn.

I can now see why a combi would require a larger supply, that was explained quite well. However, I can't see why a modern equivalent of the 20-30 would require a larger supply if they are meant to be more efficient.

Are you sure you just want to learn and it has nothing to do with that nasty con-merchant of an installer trying to extract your hard earned? Because you're repeating the same question that has been answered. As mentioned before you are assuming the existing installation is correct. Proving him right or wrong is going to cost, whichever way no-one can provide you with a inlet pressure test over the web to save this expense for you. Sorry I forgot it's nothing to do with that you're just here to learn.

I asked what I thought was a reasonable question because I was interested - take it or leave it!

I didn't say I thought the tradesman was trying to con. Also, if you read the post properly, the enquiry was on behalf of a neighbour.

I'm a tradesman myself, so I tend to be on thier side - I know all about penny pinching difficult customers.

 

[fender]

Sorry nixt,

Our posts overlapped!!

 

[doitall]

Still don't answer the question though.

Why does a modern more efficient boiler require a bigger gas pipe.

 

[Corgigrouch]

Thanks guys, interesting stuff.

What if she goes the non combi route?

The gas supply would still have to be matched to suit the needs of the boiler. The boiler would also have to bee big enough to heat both the house and the water.. Your installer would also have to take a closer look at your water cylinder and controls to make sure that they comply.. If the cylinder and controls need to be replaced/ upgraded then the savings of a slightly smaller gas supply may be wiped out

 

[holty]

just wandering if, from the op thread. is that if it is iron pipe the m3h gas rate is much higher than that off copper anyway. on certain runs

 

[doitall]

just wandering if, from the op thread. is that if it is iron pipe the m3h gas rate is much higher than that off copper anyway. on certain runs

True but the 15mm will only support 18Kw

 

[Spooked]

nixt.
Why the sarcasm?, this is a public forum and he can ask as many questions as many times as he likes, as i can.
If you disagree with his question or feel uncomfortable providing help, don't post.
A forum is for us laymen to get 'helpful' info.
If you can help, great, if not,....................

 

[Spooked]

fender.
No need to apologize.
Ask away, if people want to help, great .
If not, silence is the answer.
BTW, click on my user name and have a peek at my posts about pipe undersize.
I have had a nightmare with it, and it still isn't finished.
I shall be posting when it is all done to let people know that gave me help how it finished.

 

[Nixt]

nixt.
It doesn't matter that your posts 'overlapped', this is a public forum and he can ask as many questions as many times as he likes, as i can.
If you disagree with his question or feel uncomfortable providing help, don't post.
A forum is for us laymen to get 'helpful' info.
If you can help, great, if not,....................

If you could read as well as you can s*** stir, you'll see I made no objection to the question and was the first to answer the OP. My later comment was made against the usual result in posts about pipesizing where an OP continuously remains in denial despite the same answer being given by many other contributors.

If you bother to read the other posts you'll find the same pattern - OP poses question, question politely answered, OP then challenges information given ad nauseum etc.....

 

[Spooked]

nixt.
It matters not what you say.
Read your own two posts.
You are being sarcastic, the op asked for help.
There is no reason for a sarcastic answer.
I am not being nasty, you have answered me in the past, you gave me a sarcastic answer, and later you explained in usefull terms, maybe it is your nature.
I have no grief with you but when i see people asking for help, as i have, it gets annoying when those with the answers feel the need to be sarcastic.

 

[gremlin16]

fender

Theres any easy solution for your question.
A competent RGI can actually provide proof whether a gas supply pipe is adequately sized.
First of all he needs to know what the replacement boiler gas rates are, also he needs to take into consideration what other appliances are consuming gas.(Off same pipe run)
From all that he /she will be able to determine the size of pipe work needed to supply the correct volume of gas required.
Its down to basics.
More often than not experience plays an important part. If the installers decides to oversize some of the pipe work then you can rest assured he has ensures sufficient gas rate for all appliances. (especially combi boilers)
If you are still concerned ask the installer for a calculated pipe size layout.

Given the choice I personally would not opt to lifting floor boards to install larger diameter pipes, unfortunately the majority of boiler change require larger diameter pipes so we have no option but to lift boards and charge for accordingly.
To date no one has ever questioned our decision.