Gas supply size help

[Spooked]

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

 

[Nixt]

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.

I always give a factual answer to questions about pipesizing to laymen. The silliness starts only if the said laymen change their mind
and suddenly become pipesizing experts upon suggestion that their installer might be correct and money may need to be spent. In my experience in the field I've heard them all from 'it might be 28mm under the floor' to 'my neighbour's chap said he fits combi's that only require a 15mm gas pipe'. Then there's the one about 'manufacturers put a 15mm inlet so it only needs 15mm supply' excuse.

As said by a previous poster this issue is often overlooked by cowboys to undercut the reputable.

 

[Nixt]

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

If you read about pipesizing you'll find what you've just decribed, in the above, is the rule.

Pipesizing doesn't make Corgi any money, people who pay their fees do. But if you are, as you describe, a layman that won't include you.

 

[fender]

Ok,

Let's try to clear some things up....

1. Spooked, thanks for your support.
2. Thanks to all those who answered my questions
3. I have no concern over extra costs - the enquiry is on behalf of a neighbour.
4. Neighbour is not quibbling over extra costs, she simply posed the question, which the engineer made little to no attempt to answer.
5. I now understand why a combi requires a larger supply - thanks, that was answered in a simple understandable fashion.
6. I've not become a pipe sizing expert, I'm not in denial, and I'm not challenging any replies. I'm simply asking a question because I'm interested.

 

[Nixt]

Neighbour is not quibbling over extra costs, she simply posed the question, which the engineer made little to no attempt to answer.

The installer's attitude would be inexcusable in that case.

 

[fender]

Neighbour is not quibbling over extra costs, she simply posed the question, which the engineer made little to no attempt to answer.

The installer's attitude would be inexcusable in that case.

I agree.....

 

[gremlin16]

Spooked wrote

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

I totally agree with his reply, that is what we have to abide with. As long as your appliances have correct pressure at test point then I cannot see a problem.

WB 15Ri regular boiler requires 1.63M3 /hr gas rate, where as the 25Si combi needs 2.7m3/hr on max. The combi does normally need a larger dia gas pipe. Although the boiler can modulate down to 7 Kw on heating, it will still require max of 2.7m3/hr on hot water, this normally requires a larger gas supply pipe dia.

 

[fender]

Spooked wrote

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

I totally agree with his reply, that is what we have to abide with. As long as your appliances have correct pressure at test point then I cannot see a problem.

WB 15Ri regular boiler requires 1.63M3 /hr gas rate, where as the 25Si combi needs 2.7m3/hr on max. The combi does normally need a larger dia gas pipe. Although the boiler can modulate down to 7 Kw on heating, it will still require max of 2.7m3/hr on hot water, this normally requires a larger gas supply pipe dia.

Thanks Gremlin,

Believe me, I'm not trying to argue here, just trying to make sense of things through pure interest and I can only do that by posing questions.

The existing system is indirect and has worked perfectly for 25 years - no probs with water, heating or cooker etc.

As stated, the pipe is iron (about 25mm) to within 3m of the boiler. It then tee's into 15mm. One to the cooker (500mm away) and the other to the boiler (3m away with 3 bends)

I don't know the capacity of the existing boiler, but for arguments sake, lets say it's 30kw. If it's replaced with a modern equivalent (not combi) of 30kw, why would it need a larger supply if it's meant to be more efficient?

Is the pressure drop in a run of 15mm pipe over 3m with 3 bends that significant?

If the original supply was underrated, why has it worked perfectly for 25 years?

Do you see my point?

Sorry, not arguing, just inquisitive!

 

[Nixt]

Spooked wrote

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

I totally agree with his reply, that is what we have to abide with. As long as your appliances have correct pressure at test point then I cannot see a problem.

We all know this is the case. Spooked seems to believe that pipesizing diagrams/charts are rules when they are simply worked examples of how you can design to ensure the above is achieved. The same as 2 x 50p = £1 doesn't mean there's a rule against any other permutation to arrive at the same amount.

 

[doitall]

Spooked wrote

From my experience, as long as there is the right working pressure at the meter, you test each appliance with all appliances running at full pelt.
If each appliance stays within it's specified working pressures then the damn pipes big enough.
Too many rules and regs that make many people, namely corgi big wigs, too much money.

I totally agree with his reply, that is what we have to abide with. As long as your appliances have correct pressure at test point then I cannot see a problem.

WB 15Ri regular boiler requires 1.63M3 /hr gas rate, where as the 25Si combi needs 2.7m3/hr on max. The combi does normally need a larger dia gas pipe. Although the boiler can modulate down to 7 Kw on heating, it will still require max of 2.7m3/hr on hot water, this normally requires a larger gas supply pipe dia.

And I totally disagree with both of you.

Thats how clients get ripped off.

An honest tradesman will work out what is needed and price according, as had the OPs engineers.

Sticking any old boiler in then surprising the customer that they need a bigger gas pipe, and charging what you like as an extra, is the work of a cowboy, so if the hat fits wear it.

Then you have the cowboy customer, who's had two honest engineers both say the pipe ain't big enough, and still don't believe them.

 

[Nixt]

If the original supply was underrated, why has it worked perfectly for 25 years?

Because you are confusing the volume required for burner pressure (which is all it needs to function) with that for working pressure (which is what it needs to ensure safety).

 

[fender]

Thanks Nixt,

Interesting stuff. Anyway, off to bed. Catch you guys later.......

 

[Nixt]

I don't know the capacity of the existing boiler, but for arguments sake, lets say it's 30kw. If it's replaced with a modern equivalent (not combi) of 30kw, why would it need a larger supply if it's meant to be more efficient

In this instance you are confusing efficiency with gas pressure and flow.
Pressure and flow are worked using the boiler consumption input rate. Efficiency is a matter of how much of that energy is converted to useable heat and how much is lost out of the flue. The more efficient appliance will spend less time running at full pelt to satisfy demand. The potential rate it can burn at regardless of how short a period for will determine pipe size.

Now the installer may not have explained but everyone here has and I have to admit if you were to come out with any more of the classic old chestnuts we may be no better off. All this is open information and it might help you to read the GSIU regulations.

 

[Nixt]

Sorry OP, in mid-post missed that you had logged off. In case you come back I'll recap in layman's terms.

When renewing a boiler select one for your needs. Then it's gas rate and working pressure manufacturer's data must be observed. From there it is possible to work out the pipe size combination required (taking into account other appliances and future needs). Oversizing is not a problem. Bannish all other thoughts of past boilers, efficiencies, water flow rates etc.. they are about as relevant to this part of the job as Elton John's sex life.

 

[Agile]

To the OP.

Perhaps I can explain the situation to you?

Many older boilers were installed some time ago before CORGI existed.

Since then it has become a legal requirement for anyone working on gas to be registered with CORGI.

CORGI require their registered gas people to conform quite strictly with the gas appliance manufacturers requirements for a minimum gas supply pressure at the appliance inlet with all other gas appliances working.

In addition CORGI expect their registered people to generally conform with the relevant British Standard for gas pipe sizing which lays down a mimimum pressure loss from the meter to the appliance of just 1 mB or 5%.

So, to sum up, CORGI installers are now required to fit gas supplies to a higher standard than previously. This will often involve upgrading to a larger gas supply pipe size.

Its just stricter enforcement !

Tony