CH pipe sizes

[Stephen]

Hello,

I have 22mm pipe that goes from the boiler to a tee where it is reduced into two 15mm branches: one branch serves upstairs front radiators; the second branch serves the upstairs rear radiators. It's the same set-up for the downstairs radiators: 22m pipe tees to 15mm for the front and another 15mm for the back. And finally there's a

22mm pipe that goes to the hot water cylinder.

I'm having a bit of a rearrange of pipes ready for my new boiler and I wondered if all three feed pipes go upstairs (to pump and valves in airing cupboard) will one 22mm return pipe be sufficient to carry the combined returns? Logic suggests if three pipes carry water up, I would need three pipes to bring the water back down? Or would the one

22mm pipe cope, the flow in the return pipe just being faster than in the individual feed pipes?

I'm thinking of bringing the pump and valves downstairs to the boiler, to create space in the airing cupboard and reduce the noise at night.

Thanks, Stephen

[The Medway Handyman]

Dunno, but the cross sectional area of a 22mm pipe is just over twice that of a 15mm pipe if that helps, so presumably 1 x 22mm can carry slightly more that 2 x 15mm?

[Michael Chare]

I am note sure that I fully follow what you propose, but if the flow and return to the boiler are both 22mm pipe at the moment then I would not expect you to need a larger pipe anywhere in the system - given a normal sized house.

If you don't have a sealed system, then you need to ensure that the header tank feed and the overflow are always unobstructed.