My daughter is getting in some quotes for a new boiler in her flat: a
Worcester-Bosch 24i combi rather than the present Ideal(?) sealed
cylinder system.

Latest to quote has said that the 22mm gas supply needs to be replaced
by 28mm. None of the others have mentioned this.

There's around 16M of pipe and 10 or 12 elbows between the meter and the
boiler. Does the need to increase from 22mm to 28mm sound plausible?

If it does, does it need to be the full 16M?

TIA

--
Frank
(Beware of spam trap - remove the negative)

"F" wrote in message
...
My daughter is getting in some quotes for a new boiler in her flat: a
Worcester-Bosch 24i combi rather than the present Ideal(?) sealed cylinder
system.

Latest to quote has said that the 22mm gas supply needs to be replaced by
28mm. None of the others have mentioned this.

There's around 16M of pipe and 10 or 12 elbows between the meter and the
boiler. Does the need to increase from 22mm to 28mm sound plausible?

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do your own
calculation

If it does, does it need to be the full 16M?

ball park, pretty much so, but do your own calculation

Jim A

On 03/02/2007 12:16 Jim Alexander wrote:

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do your own
calculation

Thanks: just what I wanted.

It looks like the effective pipe length is 22.5M and the boiler + gas
fire will need 3.1M3/hr. At that rate the maximum run of 22mm is ~18.5M.

I'm stuck for how to calculate how much of the 22mm would need to be
replaced by 28mm to get the required flow.

Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers the
3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run be
28mm and 2/3 22mm?

Any help gratefully received!

--
Frank
(Beware of spam trap - remove the negative)

"F" wrote in message
...
On 03/02/2007 12:16 Jim Alexander wrote:

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do your
own calculation

Thanks: just what I wanted.

It looks like the effective pipe length is 22.5M and the boiler + gas fire
will need 3.1M3/hr. At that rate the maximum run of 22mm is ~18.5M.

I'm stuck for how to calculate how much of the 22mm would need to be
replaced by 28mm to get the required flow.

Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers the
3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run be
28mm and 2/3 22mm?


Doubt its a simple ratio because the the first pipework section will carry
fire+cooker+boiler and so there will be more allowable pressure drop in that
section. As a guide, taken from my spreadsheet calculation, no guarantees
although it worked out OK in practice, for a 28kW boiler, fire and cooker,
50% of the allowable pressure drop occurs in the first effective 4.5m of
22mm compared with effective 11.1m of 28mm. Not what your gut feeling is
though I stand to be corrected.

Jim A

In an earlier contribution to this discussion,
F wrote:

On 03/02/2007 12:16 Jim Alexander wrote:

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do
your own calculation

Thanks: just what I wanted.

It looks like the effective pipe length is 22.5M and the boiler + gas
fire will need 3.1M3/hr. At that rate the maximum run of 22mm is
~18.5M.
I'm stuck for how to calculate how much of the 22mm would need to be
replaced by 28mm to get the required flow.

Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers
the 3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run
be 28mm and 2/3 22mm?

Any help gratefully received!

It's best to turn the calculation upside down and work out pressure drop per
metre for both 22mm and 28mm pipe at your required flow rate. You can then
work out the total drop for various combinations, and find one which keeps
you within the required 1mB.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Sat, 03 Feb 2007 12:16:37 +0000, Jim Alexander wrote:

"F" wrote in message
...
My daughter is getting in some quotes for a new boiler in her flat: a
Worcester-Bosch 24i combi rather than the present Ideal(?) sealed cylinder
system.

Latest to quote has said that the 22mm gas supply needs to be replaced by
28mm. None of the others have mentioned this.

There's around 16M of pipe and 10 or 12 elbows between the meter and the
boiler. Does the need to increase from 22mm to 28mm sound plausible?

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do your own
calculation

If it does, does it need to be the full 16M?

ball park, pretty much so, but do your own calculation


Agreed. It's quite difficult to install truly compliant pipework.
See BS 6891 linked below.
Inspection and monitoring although not frequent has real teeth.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Sat, 03 Feb 2007 16:14:31 +0000, Roger Mills wrote:

In an earlier contribution to this discussion,
F wrote:

On 03/02/2007 12:16 Jim Alexander wrote:

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do
your own calculation

Thanks: just what I wanted.

It looks like the effective pipe length is 22.5M and the boiler + gas
fire will need 3.1M3/hr. At that rate the maximum run of 22mm is
~18.5M.
I'm stuck for how to calculate how much of the 22mm would need to be
replaced by 28mm to get the required flow.

Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers
the 3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run
be 28mm and 2/3 22mm?

Any help gratefully received!

It's best to turn the calculation upside down and work out pressure drop per
metre for both 22mm and 28mm pipe at your required flow rate. You can then
work out the total drop for various combinations, and find one which keeps
you within the required 1mB.

There is also a method shown in BS 6891 (linked below) where by each
segment is allowed a proportion of the 1mbar pipe work loss.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

"F" wrote in message
...
My daughter is getting in some quotes for a new boiler in her flat: a
Worcester-Bosch 24i combi rather than the present Ideal(?) sealed cylinder
system.

Latest to quote has said that the 22mm gas supply needs to be replaced by
28mm. None of the others have mentioned this.

There's around 16M of pipe and 10 or 12 elbows between the meter and the
boiler. Does the need to increase from 22mm to 28mm sound plausible?

If it does, does it need to be the full 16M?

No.

"Jim Alexander" wrote in message
...

"F" wrote in message
...
On 03/02/2007 12:16 Jim Alexander wrote:

yes, see http://www.cda.org.uk/megab2/build/pub124/sec3.htm and do your
own calculation

Thanks: just what I wanted.

It looks like the effective pipe length is 22.5M and the boiler + gas
fire will need 3.1M3/hr. At that rate the maximum run of 22mm is ~18.5M.

I'm stuck for how to calculate how much of the 22mm would need to be
replaced by 28mm to get the required flow.

Is it a simple ratio? At 15M 28mm delivers 7.0M3 while 22mm delivers the
3.4 needed, ie roughly 2:1. So, on that basis, should 1/3 of the run be
28mm and 2/3 22mm?


Doubt its a simple ratio because the the first pipework section will carry
fire+cooker+boiler

Boilers should have their own dedicated supply back to the meter.

On Tue, 06 Feb 2007 17:20:36 +0000, Doctor Drivel wrote:

Boilers should have their own dedicated supply back to the meter.

http://groups.google.co.uk/groups/se... earch+Groups

"John Stumbles" wrote in message
news
On Tue, 06 Feb 2007 17:20:36 +0000, Doctor Drivel wrote:

Boilers should have their own dedicated supply back to the meter.

http://groups.google.co.uk/groups/se... earch+Groups


Yep. A dedicated supply back to the meter. Simple. Anyone whop say
otherwise doesn't know this business.