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Old September 28th 08, 07:18 PM posted to uk.d-i-y
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Default How do I calculate gas pipe size?

Folks,

In the process of installing a new boiler, but am not really sure how I
should calculate the gas pipe size to the boiler.

The gas meter is just under 5 meters away (as the pipes will run) and this
will be the only gas appliance in the house (the Kitchen is the opposite
direction to the boiler too, so if any gas is needed or there, it won't need
to branch off of the run the the boiler)

Can someone possibly help me understand how to calculate this!?

(There will need to be two bends in the pipe, I assume swept bends are going
to be preferable here?)

Many thanks!


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Old September 28th 08, 08:30 PM posted to uk.d-i-y
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Default How do I calculate gas pipe size?

Toby wrote:
Folks,

In the process of installing a new boiler, but am not really sure how
I should calculate the gas pipe size to the boiler.

The gas meter is just under 5 meters away (as the pipes will run) and
this will be the only gas appliance in the house (the Kitchen is the
opposite direction to the boiler too, so if any gas is needed or
there, it won't need to branch off of the run the the boiler)

Can someone possibly help me understand how to calculate this!?

(There will need to be two bends in the pipe, I assume swept bends
are going to be preferable here?)

Many thanks!


I'm no expert in these matters but we have a similar setup in our house and
we have 18mm up to about 1m away from the boiler where it reduces to 15mm.


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Old September 28th 08, 08:38 PM posted to uk.d-i-y
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Default How do I calculate gas pipe size?

Toby wrote:

In the process of installing a new boiler, but am not really sure how I
should calculate the gas pipe size to the boiler.


You need two things - the maximum gas flow rate (in m^3/hour) the boiler
will draw (this will depends on its max power input). and the tables
from this document:

http://www.cda.org.uk/megab2/build/p...tallations.pdf

The gas meter is just under 5 meters away (as the pipes will run) and
this will be the only gas appliance in the house (the Kitchen is the
opposite direction to the boiler too, so if any gas is needed or there,
it won't need to branch off of the run the the boiler)

Can someone possibly help me understand how to calculate this!?


Basically assume the boiler needs at least 20mBar dynamic pressure at
its input. The governor at the meter will be set to supply at 21mBar,
therefore your pipe needs to drop no more than 1mBar dynamic pressure.

(There will need to be two bends in the pipe, I assume swept bends are
going to be preferable here?)


From memory, an elbow counts as an equivalent length of 0.5m of pipe,
and a bend as 0.3m equivalent. So if you have five meters of pipe with
two bends, then that is an effective length of 5.6m.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Old September 29th 08, 12:05 AM posted to uk.d-i-y
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Default How do I calculate gas pipe size?


"John Rumm" wrote in message
et...
Toby wrote:

In the process of installing a new boiler, but am not really sure how I
should calculate the gas pipe size to the boiler.


You need two things - the maximum gas flow rate (in m^3/hour) the boiler
will draw (this will depends on its max power input). and the tables from
this document:

http://www.cda.org.uk/megab2/build/p...tallations.pdf

The gas meter is just under 5 meters away (as the pipes will run) and
this will be the only gas appliance in the house (the Kitchen is the
opposite direction to the boiler too, so if any gas is needed or there,
it won't need to branch off of the run the the boiler)

Can someone possibly help me understand how to calculate this!?


Basically assume the boiler needs at least 20mBar dynamic pressure at its
input. The governor at the meter will be set to supply at 21mBar,
therefore your pipe needs to drop no more than 1mBar dynamic pressure.

(There will need to be two bends in the pipe, I assume swept bends are
going to be preferable here?)


From memory, an elbow counts as an equivalent length of 0.5m of pipe, and
a bend as 0.3m equivalent. So if you have five meters of pipe with two
bends, then that is an effective length of 5.6m.


Okay, thanks for that, on reading the link, you are quite correct, an elbow
is 0.5m and a bend is 0.3m.

The boiler is a Vaillant EcoTEC 837, which is 37Kw. According to the manual
needs up to 4M3/hour

It actually says "Connected load (if needed, related to stored charge/water
heating) at 15 °C and 1013 mbar"
Would that be the max it needs, as I can't see any other gas requirements
listed?

If I am understanding this correctly, a 6m run of 22mm will give me 5.8 m3/h
at 20mbar, so that's going to be fine. Even if the length was 9m, the
delivery would be 4.6M3/h at 20mbar, so I am well within tolerance here.

Toby...

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Old September 29th 08, 01:33 AM posted to uk.d-i-y
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Default How do I calculate gas pipe size?

Toby wrote:

From memory, an elbow counts as an equivalent length of 0.5m of pipe,
and a bend as 0.3m equivalent. So if you have five meters of pipe with
two bends, then that is an effective length of 5.6m.


Okay, thanks for that, on reading the link, you are quite correct, an
elbow is 0.5m and a bend is 0.3m.

The boiler is a Vaillant EcoTEC 837, which is 37Kw. According to the
manual needs up to 4M3/hour


Well if you take a m^3 of gas as 38.2MJ, then 37kW will require 133 MJ/h
or 3.5 m^3 ish. So 4 sounds like a generous top limit to work to.


If I am understanding this correctly, a 6m run of 22mm will give me 5.8
m3/h at 20mbar, so that's going to be fine. Even if the length was 9m,
the delivery would be 4.6M3/h at 20mbar, so I am well within tolerance
here.


Yup, that sounds plausible. When I did my boiler it was 35kW and IIRC
the max run of 22mm I calculated I could use was 12m. In reality I only
needed 6, which I did in mostly 22 and only dropped to 15 at the union
on the boiler. Dynamic pressure was fine.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/


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