extending a central heating system


13 Nov 2003
Reaction score
United Kingdom
Hi and thanks in advance for any input / solutions.

We bought a pair of flats that were halfway done to becoming a single house, the central heating system is in and working but only upstairs. I have checked the capacity of the boiler and hung the appropriate radiators downstairs, measured up and bought piping, fittings etc.
Heres the thing!
I was originally gonna just extend from the 15mm piping upstairs with 15mm piping to downstairs and therough to all radiators, however a friend has pointed out that I should extend the 22mm pipe from the boiler and take that downstairs then reduce to 15mm pipe, erm... That would cause me great difficulty sighting where the 22mm runs and ends(reduces to 15mm) upstairs and where i want to take the pipes downstairs! (im getting confused writing this!)
I can't (nieve) see the point of doing this, he says it will increase the flow, but if i reduce to 15mm when its downstairs then surley the flow is only increased very sliightly, can I use my original plan, or is it back to the drawing board for me?

A; 15mm extending downstairs from the upstairs 15mm loop.

B; 22mm extending downstairs from the upstairs 22mm.

Thanks again

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If you're clever you might get it to work with 15mm throughout. I would take notice of your friend and use 22mm until you can go down to 15mm. This isn't just hit and miss, you need to have pipes to carry the amount of water needed to move the heat. If you can move more water, you have some margin. It will also not give you so much rouble when you neglect the system, as you will.

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