The above mis-leading advice is the reason threads get locked , had you of given the correct advice Ianmcd would have had no reason to question it.
Advice from non professionals like yourself would be the reason these threads get locked.
The advice you gave the OP was incorrect , whether it is understood is neither here nor there.
I clearly understood what you said regarding the max load for 15mm tube being 3kw...I also understand that what you said was complete and utter nonsense.
Hopefully you will exactly understand what I have said.
I detect a bit of animosity here.
Excuse me for asking but with regards to my original query is it okay or not?
I'd appreciate a layman's answer if possible.
It'll work, just about. It's pushing it though. You'd be best doing a separate run for each radiator if you can. You may well have to balance other radiators to get the new ones to heat up well (see the FAQ at the top of this forum).
The "debate" above is because a pipe can only flow a certain amount of heat (energy) - proportional to the amount of, and temperature of water that flows through it. If the temperature is relatively fixed (the boiler's flow temperature) then that amount of heat is proportional to the velocity of water through the pipe. The velocity goes up the harder the pump pushes, but so does the noise. The longer the pipe run, the more resistance to flow their is and the slower the water will go.
It's quite complex fluid dynamics. That's why there are "rules of thumb" which are based on experience of what works and what doesn't. However, it is completely and utterly irrelevant what kind of boiler you have.
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