extending a central heating system


13 Nov 2003
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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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Post this in the plumbing section for a quicker response............

Masona is right but i have moved it. (MODERATOR)
Basically you can think of the heating system a bit like the human body. The 22mm pipes are the arteries supplying hot water from the boiler (the heart) and is supplying a number of radiators via reduced 15mm pipes (veins) i.e. you want the veins comming off the artery, not a vein supplying a load of other veins else you have a bottle neck.

Basically if you were to take the 15mm pipe down stairs and run a load of rads off it, you would have a bottle neck and will be limiting the max number of rads you could take off this 15mm pipe. However, my central heating at home is exactly like this, think it was put in a long time ago, by some billy bodge it council contractors? and it seems to work okay?

What a load of old waffle. Basically, i think, you shouldn't run the 15mm downstairs to supply your rads but many people do? Best wait for one of the experts to respond, as i know nothing ;)

here's the science http://www.diydata.com/planning/ch_design/sizing_pipes.htm
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When I did mine I didn't use any 22mm downstairs. It's a lot easier to tap off the 22mm upstairs. You will have to lift a few floor boards, find the 22mm as close as possible to the wall where the downstairs rad is sited, then branch off the 22 pipe, through the ceiling and down the wall. As mentioned before, you want to try and minimise the amount of rads you run off a 15mm pipe, although you could probably get away with 2 or 3, it's best to keep them all branching off the 22 pipe.

Good luck!
[it all depends how big your boiler is (kw)
if you have 15mm pipe coming off 22 you are able to run 15kw which is normally 3 big rads, when you start running 15 from upstairs to downstairs your not going to get the heat to all the radiators.
My best opinion to you would be to exstend the 22 as you will be able to supply heating to all the downstairs.

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