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i am fitting the pipe work for my central heating system and using 22mm from the boiler.
What is the recommended or maximum distance i could run 10mm feeds to the radiators from the 22mm main flow and return pipes.
The system is a dual zone, with flow and returns for upstair and downstairs.
The boiler will be a keston with a 300 litre megaflow.

thanks for your help
simon

First you need to establish the heat losses for the rooms.
Second establish the size of the radiator/radiators required.
Then work out the sizes of pipes needed taking into account the heat required, the water speed through the pipe, the distance from the boiler (heat loss). The smaller the pipe diameter the cheaper the pipe the harder the pump will work. Larger pipe equalls less pressure, less noise but, more water to heat and greater heat loss.
Summing up 10mm pipe will not suit every situation, a large radiator running nearby, a small radiator further away. Once you know the heat required, the boiler temperature, the heat loss per metre, friction costs, then the length falls into place.

Keston - very nice, sounds like it will be a good system.

Presumably it will be an S plan configuration with the indirect cylinder in parallel with the central heating. Don't forget the bypass valve for when both 2 way valves are closed.

Also if you're not using a pressurised heating loop, Keston often recommend a sinle 28mm pipe to the expansion tank instead of a more normal 15mm +22mm configuration.

Bit concerned about the use of 10mm in this particular sysytem as, with the indirect cylinder in parallel, the central heating could be struggling to get a share of the hot water from the boiler when there is simultaneous demand for hot water. Might be best not to go below 15mm.

ain You will