My Ch is built on a 10mm system .Just a thought .Would there be any problems in systematically changing this to 15mm room by room to avoid having to do it all at the one time ..I know that the pipes from the boiler meet in the hall where there is a manifold and the 10mm pipes lead from that to each of the rads in the hall,l/room,two b/rooms and the bathroom.The trv's are all 15mm. Stuart
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I can't see why there should be any technical problems - but I'm somewhat baffled as to just why you would want to do it! Hell of a lot of work and, in addition to changing all the pipework (and manifold) you will also have to change all the radiator valves. 10mm systems work perfectly efficiently and the pipework is smaller and neater than 15 mm. Why change?
Kev
You're right Kev ..I don't really have any reason .If ,as you say,10mm systems are ok then I'll forget it but why,in that case do people use
15mm systems ..My valves are 15mm as I said so it would be the pipework that would be getting changed .Stuart
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Each time you make a change, you will have an effect on the overall system balancing.
For each radiator, the flow is determined by the combined resistancce of the pipework, the lockshield valve and the TRV.
If the pipework is not significant in that - for example if the main limitation to flow is the lockshield and TRV, then swapping that radiator to 15mm will not make a big difference. That will tend to be the case for radiators with short 10mm pipe runs.
For those further away, it is likely that the lockshield valve is more open and more of the resistance comes from the pipework. Changing these pipes will increase the flow and you may need to compensate by closing the lockshield a little.
Up to a point, the TRVs will even out the balance of flow, although you may get an effect that some radiators get all the flow and heat their rooms first, followed by their TRVs reducing the flow and directing flow elsewhere. You might want this behaviour but probably not.
Balancing radiators is time consuming and tedious. What you could do is to do a few changes and then rebalance if you notice a problem, or simply close the lockshield a bit on anything that has a short pipe run.
This does beg the question of why do you want to change the pipes....
Because sometimes it's more convenient to run all the pipework to a central point, and sometimes it's more convenient to have main pipes with radiators off.
A bit like the difference between ring and radial socket circuits. Depends on the application.
Owain
There's no magic or fundamental difference in any pipe size. The main criterion is the max flow rate that can be achieved through a given diameter of pipe without excessive noise and turbulence.
The copper tube suppliers recommend no more than 1.5m/sec for this. You can work out everything else from there. A radiator is sized based on compensating the heat loss for the room - so many watts are required. In order to achieve this output, for a given temperature drop, which is also known, you can calculate the mass of water per second that needs to flow. From that, you can determine the pipe size from tables of data.
A rule of thumb is that 8mm pipe will support 1.5kW over typical domestic distances of a few metres and 10mm will support 2.5kW. As long as the radiators are under that size, then all will work OK.
The installation techniques are somewhat different. 8 and 10mm tube is typically used with a manifold (but doesn't have to be), and 15mm is done as branches normally from a 22mm run. It is often possible to run two or more radiators from a single 15mm pair of pipes from a 22mm main run - one has to do the sums to work out the flow. With 8 and
10mm, the tubes are normally run back to the manifold fo each radiator.If you want to read up on how this is done, the web site of the Copper Development Association has some useful information and design papers.
I have a system that is based entirely on 8mm tube. Some of the larger rooms have multiple radiators of 1.5kW or less.
This all works fine, so there is no reason to change a working system.
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