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Default Central heating system - acceptable use of 15mm pipes?


About ten years ago, I installed a central heating for two one-bed
flats in my house. The boiler is in the loft and the flats are
respectively in the ground floor and 1st floor. The only 22mm pipe I
used was the feed and return from the boiler to each of the central
heating circuits. The pipework within each flat's circuit is all 15mm.

I later learned that I should (according to the conventions) have used
22mm pipe for the 'rings' of each circuit too, with 15mm pipe used
only for the short spurs going to and from each rad. Nevertheless, the
system has worked perfectly for ten years.

I now want to give the Ground floor flat its own combi boiler, and
isolate that circuit from the rest of the house. In view of the fact
that the entire system has worked fine for ten years, is there any
point in adding any 22mm pipe to the ground floor circuit when I add
the new boiler? Can I simply use 15mm for the feed and return from the
new boiler? The furthest radiator will be just under twelve meters'
pipe-length away from the new boiler.

Thank you,

Duke D
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Default Central heating system - acceptable use of 15mm pipes?

On Tue, 15 May 2007 17:37:16 +0100 someone who may be DukeD
wrote this:-

About ten years ago, I installed a central heating for two one-bed
flats in my house. The boiler is in the loft and the flats are
respectively in the ground floor and 1st floor. The only 22mm pipe I
used was the feed and return from the boiler to each of the central
heating circuits. The pipework within each flat's circuit is all 15mm.

I later learned that I should (according to the conventions) have used
22mm pipe for the 'rings' of each circuit too, with 15mm pipe used
only for the short spurs going to and from each rad.


15mm pipe can feed a few normal house sized radiators without great
problem. Beyond that the flow velocity necessary to transport the
necessary amount of heat gives rise to noise.

Conventions tend to be conservative.

I wouldn't do anything to the pipework if changing the boiler.


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David Hansen, Edinburgh
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Default Central heating system - acceptable use of 15mm pipes?

On 2007-05-15, DukeD wrote:
I now want to give the Ground floor flat its own combi boiler, and
isolate that circuit from the rest of the house. In view of the fact
that the entire system has worked fine for ten years, is there any
point in adding any 22mm pipe to the ground floor circuit when I add
the new boiler? Can I simply use 15mm for the feed and return from the
new boiler? The furthest radiator will be just under twelve meters'
pipe-length away from the new boiler.


I'm not an expert but what I think matters is that you have an acceptable
flow rate in the pipes. For any particular pipe diameter the upper
limit (there is a lower limit too) is determined by pipe erosion (and
flow noise).

For 11 C drop across the radiators the CDA (Copper Development
Association) seems to say in table 2 of:

http://www.cda.org.uk/megab2/build/p...ng-systems.pdf

that a 15 mm pipe will deliver up to 9.2 kW total output to radiators
(that's 0.2 kg/s of water flow - beware of some fairly obvious incorrect
tabulation in table 2).

I suspect that may possibly be a little high from the noise POV. In my
recent upgrade to a small CH system I used 15 mm pipes where the total
power carried was 6.5 kW or less, and 22 mm elsewhere. It's adequately
quiet at that level.

--
John Phillips
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Default Central heating system - acceptable use of 15mm pipes?

In an earlier contribution to this discussion,
John Phillips wrote:

On 2007-05-15, DukeD wrote:
I now want to give the Ground floor flat its own combi boiler, and
isolate that circuit from the rest of the house. In view of the fact
that the entire system has worked fine for ten years, is there any
point in adding any 22mm pipe to the ground floor circuit when I add
the new boiler? Can I simply use 15mm for the feed and return from
the new boiler? The furthest radiator will be just under twelve
meters' pipe-length away from the new boiler.


I'm not an expert but what I think matters is that you have an
acceptable flow rate in the pipes. For any particular pipe diameter
the upper limit (there is a lower limit too) is determined by pipe
erosion (and flow noise).

For 11 C drop across the radiators the CDA (Copper Development
Association) seems to say in table 2 of:

http://www.cda.org.uk/megab2/build/p...ng-systems.pdf

that a 15 mm pipe will deliver up to 9.2 kW total output to radiators
(that's 0.2 kg/s of water flow - beware of some fairly obvious
incorrect tabulation in table 2).

I suspect that may possibly be a little high from the noise POV. In
my recent upgrade to a small CH system I used 15 mm pipes where the
total power carried was 6.5 kW or less, and 22 mm elsewhere. It's
adequately quiet at that level.



The rule of thumb often quoted here is a max of 6kW for 15mm pipe.
--
Cheers,
Roger
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Default Central heating system - acceptable use of 15mm pipes?

On Tue, 15 May 2007 17:50:55 +0100, David Hansen
wrote:

Conventions tend to be conservative.

I wouldn't do anything to the pipework if changing the boiler.


Many thanks for the replies. For once I made a mistake that turned out
to my advantage!

Duke

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