condensing boiler gas supply is 15mm ok

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wennners

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Hi Gents can you please answer a question for me, we are having our old combi boiler replaced with a new condensing combi.

The old gas supply to the boiler is 15mm and we have been told the supply needs to be in 22mm? Is this correct?

If so the gas pipe runs underneath the bathroom flooring to where the boiler is in the bathroom and would therefore need to be ripped up including the removal of a shower enclosure and floor tiles?

Thanks in advance for your advice
 
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Almost certainly 22mm at least, don't know why it couldn't run externally though.
 
15mm could also be okay. Providing you have the correct inlet pressure at the appliance (per manufacturers instructions) and are within your permissable pressure loss tolerances......who gives a stuff??
 
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What boiler is being fitted?...this isn't a RGI whim, its defined by length of gas pipe run (pipe sizing based on gas requirements per appliance) and manufacturers instructions. There are some boilers still out there that accept 15mm gas supplies but they are in the minority now, most need 22mm........
 
Why second guess your Plumber

do you think he is incompetant?

If we had agreed with you would you have taken the word of people you dont know from t'ternet over that of someone whos bona fidas you could actually check??
 
corgiman said:
Why second guess your Plumber

do you think he is incompetant?

If we had agreed with you would you have taken the word of people you dont know from t'ternet over that of someone whos bona fidas you could actually check??
Click to expand...

Because, as I've said before, the facts about pipe sizing, amongst many punters, is taboo to the point where if it were endorsed by everyone from Matt Allwight to David Beckham, they would sooner take advice from Robert Mugabe if it meant keeping the existing 15mm supply.
 
The reason for asking is that we have been advised different things by different people. some times its hard to know what to believe, therefore it is beneficial to ask the question on here and to get an answer which is not tainted by having a vested interest on how much you can charge. It’s not a case of taking yours over other views but more backing up what we have been told.

Believe it or not i have found that by reading responses to questions on a web site like this you tend to get more honest answers as you answer the question asked and have no thoughts on any other issues. Plus if someone give a bogus answer there usually is someone who rebuke what they say.

corgiman said:
Why second guess your Plumber

do you think he is incompetant?

If we had agreed with you would you have taken the word of people you dont know from t'ternet over that of someone whos bona fidas you could actually check??
Click to expand...
 
Regardless of what anyone says, if your boiler is supplied with a 22mm tail for the gas connection, then all MI's usually state that you must not connect to a gas supply that is smaller than the tail they have supplied.

What boiler is it?
 
as already mentioned...cant it go on the outside of the house and through the wall near the boiler...or up into the loft and down to the boiler (albeit more elbows etc, but a few more lengths of 28mm will be cheaper than taking shower out and tiles )
 
A 35KW combi boiler on full demand will require 3.7m3/h of NG therefore you can probably only use about one mtr of 15mm with no elbows or tees and no other appliances connected to deliver this amount of gas (3mts of 15MM delivers 2.9m3/h).

However you can run 12mtrs of 22m (3.9m3/h) without bends or tees and other appliances or 30mtrs of 28MM (4.7m3/h) in the same way/setup.

Each elbow and tee adds 0.5mtrs to the pipe length with a swept elbow adding 0.3 mtrs which reduces the amount of gas that can pass through the pipe.

EG, six elbows and two tees equals 4mtrs so the 22 mm pipe length becomes 16mtrs which can pass only 3.3m3/h approx thus requiring 28mm pipe to be used to deliver the 3.7m3/h of NG.
 
I daresay tonybhoy is spot on with his numbers.

But anyone who installs knows that the tables are miles out. Then the outlet of the meter is usually small, etc etc.
I usually work it out, then go the next size up!

FOr example, I just put in a 28kw combi.
20metres of 28mm pipe, all completely deburred, 10 elbows, and a little 22mm coming off the meter.
Drop shows the pipe is undersized. Go figure.
 
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