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

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

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.

Reply to
David Hansen

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:

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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.

Reply to
John Phillips

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> that a 15 mm pipe will deliver up to 9.2 kW total output to radiators

The rule of thumb often quoted here is a max of 6kW for 15mm pipe.

Reply to
Roger Mills

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

Duke

Reply to
Duke

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