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thescullster
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

Hi all

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of the
current boiler.
Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat input
required.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned on?

As we have concrete floors throughout and the boiler location is as far from
the meter as geographically possible, what are the alternatives (please
don't suggest moving)?

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?
Final question - if the gas supply pressure as measured is high, can I take
this into account in calculation? I believe 20mBar is the datum pressure on
which these figures are based?


TIA as ever

Phil


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Andy
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"thescullster" wrote in message
...
Hi all

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of
the current boiler.
Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat
input required.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned
on?

As we have concrete floors throughout and the boiler location is as far
from the meter as geographically possible, what are the alternatives
(please don't suggest moving)?

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?
Final question - if the gas supply pressure as measured is high, can I
take this into account in calculation? I believe 20mBar is the datum
pressure on which these figures are based?


TIA as ever

Phil


Have you seen this site?

http://www.cda.org.uk/megab2/build/pub124/sec3.htm#4.3

You need to convert BTU and kW into cu.m/hour, but you can do that from
your bill, I believe 1cu.m natural gas = 1,117 kW/h, or 1 unit ( =1
cu.foot )
=31.4 kW/H, give or take a little ( it varies with the gas content and
atmospheric pressure ).

As for your gas pressure, the usual quoted spec for an appliance at full
kilter is 20mBar +/- 1mBar, so if your gas governor gave a higher pressure
than that yes, that could work to your advantage. Remember though, the
governor attached to your gas meter only works when there is a load on i
i.e. someting is drawing gas. It will read perhaps 26mBar or higher if you
measure its output when nothing is drawing gas.

Andy.


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Gav
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

thescullster wrote:
Hi all

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of the
current boiler.
Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat input
required.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned on?

As we have concrete floors throughout and the boiler location is as far from
the meter as geographically possible, what are the alternatives (please
don't suggest moving)?

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?
Final question - if the gas supply pressure as measured is high, can I take
this into account in calculation? I believe 20mBar is the datum pressure on
which these figures are based?


TIA as ever

Phil


the easiest way to see if the installation pipework is to find the
'standing' pressure at the current appliance, then if it is 21 mbar - 1
mbar for pipework, it should be ok, any less then you may need to resize
but as yet, i think, 22mm is the standard maximum pipe size, although i
think it will be moving to 32 or 35 with the advent and realisation of
new technology
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John Stumbles
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Thu, 01 Jun 2006 20:38:36 +0100, thescullster wrote:

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of the
current boiler.


22mm copper, not 3/4" outside diameter steel, right? The latter is 1/2"
bore.

Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat input
required.


If it's 4m from the meter I'd guess (without doing the calcs for you,
which you seem capable of doing yourself, with Treloar's help) that it
won't make too much difference.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned on?


In practice, none.

As we have concrete floors throughout ...


Ahem! you say 22mm pipe, suggesting copper rather than steel. Now you say
concrete floors. Errr, it _is_ adequately protected where it's laid in the
concrete, isn't it?

.... and the boiler location is as far from
the meter as geographically possible, what are the alternatives (please
don't suggest moving)?


If you replaced accessible lengths with 28mm and/or 22mm elbow bends with
swept bends you could reduce the effective length by perhaps a few metres.

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?


Maybe. Maybe it was under-specced for that lot. Quite possibly they added
appliances without calculating & checking (shouldn't have, of course).

Final question - if the gas supply pressure as measured is high, can I
take this into account in calculation?


No. It has to be 1mBar drop in the pipework. (If the meter regulator is
high when you install the appliance and subsequently gets re-set correctly
are you going to shut down the appliance because the pressure is now below
spec?)

In practice one sees a lot of installations in which the drop is
1mBar. If I came across one I wouldn't be worried as long as the pressure
is still reasonable, and far enough above the boiler's required burner
pressure not to affect operation. However in installing an appliance one
can't take such an accomodating attitude but should do it by the book.
  #5   Report Post  
Posted to uk.d-i-y
TheScullster
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

First of all, thanks to all respondents for useful comment


"John Stumbles" wrote

22mm copper, not 3/4" outside diameter steel, right? The latter is 1/2"
bore.


Yes original 22mm copper in 1970s build.


Ahem! you say 22mm pipe, suggesting copper rather than steel. Now you say
concrete floors. Errr, it _is_ adequately protected where it's laid in the
concrete, isn't it?


Again the installation is original.
Haven't had need to expose the gas, but the heating pipes are wrapped in
hession type stuff, laid in a sand filled channel and concreted over.
Does this constitute adequate protection?


If you replaced accessible lengths with 28mm and/or 22mm elbow bends with
swept bends you could reduce the effective length by perhaps a few metres.


Unfortunately, nearly all is buried.


Final question - if the gas supply pressure as measured is high, can I
take this into account in calculation?


No. It has to be 1mBar drop in the pipework. (If the meter regulator is
high when you install the appliance and subsequently gets re-set correctly
are you going to shut down the appliance because the pressure is now below
spec?)

In practice one sees a lot of installations in which the drop is
1mBar. If I came across one I wouldn't be worried as long as the pressure
is still reasonable, and far enough above the boiler's required burner
pressure not to affect operation. However in installing an appliance one
can't take such an accomodating attitude but should do it by the book.




From the various responses and Treloar, I believe that the installation
should be OK.
Will put the onus on the installer to confirm and check pressures though.

Thanks for the comprehensive response

Phil




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Posted to uk.d-i-y
John Stumbles
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Fri, 02 Jun 2006 13:54:55 +0100, TheScullster wrote:

"John Stumbles" wrote


Ahem! you say 22mm pipe, suggesting copper rather than steel. Now you
say concrete floors. Errr, it _is_ adequately protected where it's laid
in the concrete, isn't it?

Haven't had need to expose the gas, but the heating pipes are wrapped in
hession type stuff, laid in a sand filled channel and concreted over.


Hair felt

Does this constitute adequate protection?


No, unfortunately not. At least, not by current standards - I don't know
what was required in 1978 but if I came across an installation like
that now I'd have to label it At Risk since, for all I know, the last thou
of copper might be about to corrode through and spout a leak.

The pipework should be protected by suitable wrapping tape or by being
coated with a bituminous paint. At the time of your installation a
suitable tape would probably have been grease-filled cloth ('Denso' tape).
(In the current British Standard this is no longer allowed and PVC tape
should be used instead.)

Can you carefully expose a bit of the buried pipework to see if it's
properly wrapped?


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Doctor Drivel
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"TheScullster" wrote in message
...
First of all, thanks to all respondents for useful comment

"John Stumbles" wrote

22mm copper, not 3/4" outside diameter steel, right? The latter is 1/2"
bore.


Yes original 22mm copper in 1970s build.

Ahem! you say 22mm pipe, suggesting copper rather than steel. Now you say
concrete floors. Errr, it _is_ adequately protected where it's laid in
the
concrete, isn't it?


Again the installation is original.
Haven't had need to expose the gas, but the heating pipes are wrapped in
hession type stuff, laid in a sand filled channel and concreted over.
Does this constitute adequate protection?

If you replaced accessible lengths with 28mm and/or 22mm elbow bends with
swept bends you could reduce the effective length by perhaps a few
metres.


Unfortunately, nearly all is buried.

Final question - if the gas supply pressure as measured is high, can I
take this into account in calculation?


No. It has to be 1mBar drop in the pipework. (If the meter regulator is
high when you install the appliance and subsequently gets re-set
correctly
are you going to shut down the appliance because the pressure is now
below
spec?)

In practice one sees a lot of installations in which the drop is
1mBar. If I came across one I wouldn't be worried as long as the pressure
is still reasonable, and far enough above the boiler's required burner
pressure not to affect operation. However in installing an appliance one
can't take such an accomodating attitude but should do it by the book.


From the various responses and Treloar, I believe that the installation
should be OK.
Will put the onus on the installer to confirm and check pressures though.

Thanks for the comprehensive response


Phil

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs. Then you are certain there will be no
problems. Even doing what the sizing charts say cannot be fully guaranteed
that one appliance will not affect the other. With the crap meter
regulators Transco fit and the introduction of pre-mix burners on boilers it
is best do what I advise. Keep the boiler supply separate right back to the
meter. Been there, done it, seen it all.

  #8   Report Post  
Posted to uk.d-i-y
Andy Hall
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Fri, 2 Jun 2006 15:18:36 +0100, Doctor Drivel wrote
(in article ews.net):



Phil

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs. Then you are certain there will be no
problems. Even doing what the sizing charts say cannot be fully guaranteed
that one appliance will not affect the other. With the crap meter
regulators Transco fit and the introduction of pre-mix burners on boilers it
is best do what I advise. Keep the boiler supply separate right back to the
meter. Been there, done it, seen it all.


Been doing a spot of fitting professionally?



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Posted to uk.d-i-y
Doctor Drivel
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"Andy Hall" aka Matt wrote in message
...
On Fri, 2 Jun 2006 15:18:36 +0100, Doctor Drivel wrote
(in article ews.net):



Phil

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs. Then you are certain there will be no
problems. Even doing what the sizing charts say cannot be fully
guaranteed
that one appliance will not affect the other. With the crap meter
regulators Transco fit and the introduction of pre-mix burners on boilers
it
is best do what I advise. Keep the boiler supply separate right back to
the
meter. Been there, done it, seen it all.


Been doing a spot of fitting professionally?


Matt, as you read, I said "Been there, done it, seen it all.". Do you need
a pro in your place to put things right?

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John Stumbles
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Fri, 02 Jun 2006 15:18:36 +0100, Doctor Drivel wrote:

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs.


What 'standard' is that, then?

In the UK the current standard is BS6891:2005 "Installation of low
pressure gas pipework ... in domestic premises". Appendix A of this
standards document explicitly shows how to size pipe to supply multiple
appliances _with_ tee offs.



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Posted to uk.d-i-y
Doctor Drivel
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"John Stumbles" wrote in message
news
On Fri, 02 Jun 2006 15:18:36 +0100, Doctor Drivel wrote:

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs.


What 'standard' is that, then?

De-facto standard. I know no one who know his stuff not to have a dedicated
gas supply directly back to the meter. Many of the old area Gas Boards
would not have it any other way. Now the privateers are in charge anything
goes.

In the UK the current standard is BS6891:2005 "Installation of low
pressure gas pipework ... in domestic premises". Appendix A of this
standards document explicitly shows how to size pipe to supply multiple
appliances _with_ tee offs.


Read what I wrote and take note. If you want no problems at all have a
dedicated supply.

  #12   Report Post  
Posted to uk.d-i-y
Andy Hall
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Fri, 2 Jun 2006 15:34:59 +0100, Doctor Drivel wrote
(in article ews.net):


"Andy Hall" aka Matt wrote in message
...
On Fri, 2 Jun 2006 15:18:36 +0100, Doctor Drivel wrote
(in article ews.net):



Phil

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs. Then you are certain there will be no
problems. Even doing what the sizing charts say cannot be fully
guaranteed
that one appliance will not affect the other. With the crap meter
regulators Transco fit and the introduction of pre-mix burners on boilers
it
is best do what I advise. Keep the boiler supply separate right back to
the
meter. Been there, done it, seen it all.


Been doing a spot of fitting professionally?


Matt, as you read, I said "Been there, done it, seen it all.". Do you need
a pro in your place to put things right?


There's nothing that needs to be put right, but why don't you post your
contact details for future reference.



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Posted to uk.d-i-y
Andy Hall
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Fri, 2 Jun 2006 18:02:31 +0100, Doctor Drivel wrote
(in article ews.net):


"John Stumbles" wrote in message
news
On Fri, 02 Jun 2006 15:18:36 +0100, Doctor Drivel wrote:

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs.


What 'standard' is that, then?


De-facto standard. I know no one who know his stuff not to have a dedicated
gas supply directly back to the meter. Many of the old area Gas Boards
would not have it any other way. Now the privateers are in charge anything
goes.

What a load of old nonsense.

Liberation of the gas industry from government control was in 1986.

The requirement for high capacity gas supplies to individual appliances is
largely a phenomenon of the combi era, and combis had nothing like the market
share then that they have today.



In the UK the current standard is BS6891:2005 "Installation of low
pressure gas pipework ... in domestic premises". Appendix A of this
standards document explicitly shows how to size pipe to supply multiple
appliances _with_ tee offs.


Read what I wrote and take note. If you want no problems at all have a
dedicated supply.


Clearly you know better than the industry professionals and standards
bodies....

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Ed Sirett
 
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Default Gas Experts Required - Is Supply Pipe Size OK?

On Thu, 01 Jun 2006 20:38:36 +0100, thescullster wrote:

Hi all

Looking at a replacement central heating/HW boiler and reckon I will need
something like W/Bosch 24Ri. This states a requirement of 2.67cu.m/hr of
gas.

I have a 22mm gas pipe running right across the house to the location of the
current boiler.
Assessment of length and addition of effective length for bends etc gives
23m equivalent length of pipe.
From R D Treloar, this looks to be right on the limit for 22mm dia pipe.

Also we have a gas fire tapped off this main (approx 4 m from gas meter).
This is an occasional use decorative affair claiming 6.5Kw gross heat input
required.

Does anyone know enough to comment on the viability of this install?
What would the effect be if the boiler were running and the fire turned on?

As we have concrete floors throughout and the boiler location is as far from
the meter as geographically possible, what are the alternatives (please
don't suggest moving)?

Also I note that previously it would have been likely that this main would
serve:
Valor Homeflame gas fire
Landing gas heater
Gas cooker
CH boiler 50,000 Btu

Surely this lot would put as much if not more load on the supply?
Final question - if the gas supply pressure as measured is high, can I take
this into account in calculation? I believe 20mBar is the datum pressure on
which these figures are based?



By the book it usually possible to correctly design the pipework. In
practice the pipework in _most_ houses and flats (that I come across)
drops more than 1 mBar between meter and appliances.

The installer can't usually take the risk to reuse undersized (but
functional) pipework because the monitoring and inspection
process has real teeth.

By the book the meter supplies gas at 19-23 (used to be 20-22) mbar.
The pipework should take no more than 1 mbar so leaving 18mbar + at the
appliances.

The W/B will insist on 18mbar minimum inlet working pressure in the manual.
IIRC this is a forced premix burner so will not readily tolerate poor
inlet pressures.

In practice the meter will almost certainly be giving 22 to 20 mbar at the
outlet depending on the rate of gas flow. This means that you will almost
certainly get your 18 mbar even with the fire on at the boiler. So you
have a functional but irregular installation just almost like everyone
else.




--
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

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Doctor Drivel
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"Andy Hall" aka Matt wrote in message
...
On Fri, 2 Jun 2006 18:02:31 +0100, Doctor Drivel wrote
(in article ews.net):


"John Stumbles" wrote in message
news
On Fri, 02 Jun 2006 15:18:36 +0100, Doctor Drivel wrote:

It is standard practice to have the boiler gas supply dedicated to the
boiler only and no tee offs.

What 'standard' is that, then?


De-facto standard. I know no one who know his stuff not to have a
dedicated
gas supply directly back to the meter. Many of the old area Gas Boards
would not have it any other way. Now the privateers are in charge
anything
goes.


What a load of old nonsense.

snip lots of ill-informed Mattness



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Posted to uk.d-i-y
TheScullster
 
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Default Gas Experts Required - Is Supply Pipe Size OK?


"Ed Sirett" wrote


By the book it usually possible to correctly design the pipework. In
practice the pipework in _most_ houses and flats (that I come across)
drops more than 1 mBar between meter and appliances.

The installer can't usually take the risk to reuse undersized (but
functional) pipework because the monitoring and inspection
process has real teeth.

By the book the meter supplies gas at 19-23 (used to be 20-22) mbar.
The pipework should take no more than 1 mbar so leaving 18mbar + at the
appliances.

The W/B will insist on 18mbar minimum inlet working pressure in the
manual.
IIRC this is a forced premix burner so will not readily tolerate poor
inlet pressures.

In practice the meter will almost certainly be giving 22 to 20 mbar at the
outlet depending on the rate of gas flow. This means that you will almost
certainly get your 18 mbar even with the fire on at the boiler. So you
have a functional but irregular installation just almost like everyone
else.


Thanks for the concise, informative response Ed.
Of course, the onus will be on the installer to check all this, but I didn't
want to go too far down a blind alley with my planning process.

Phil


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