Plumbing for loft pipe sizes

[Simmoz]

Hi All,

Have 40s mid terrace supplied by lead pipe.
About to add plumbing for a new loft bathroom with toilet basin and electric shower.

Hw is supplied by greenstar 30i down stairs in kitchen.

Should the new feeds be run in 22mm to maintain pressure up there or will 15mm suffice

I assume it’s best to keep runs as short as possible
So I can just tee off at the closest point?

 

[Madrab]

15mm will still deliver the same pressure as the 22mm though it's all down to flow and that is dictated by the mains pressure and pipe size. if you have good mains pressure >2bar dynamic then 15mm would be fine, especially if the boiler and HW is 15mm.

 

[Simmoz]

I think pressure is ok. Getting 14litres min on the jug test. HW is all 15mm and existing non electric shower is perfect. I’ll go with 15mm then thanks

 

[Madrab]

Only issue you may get with 15mm is that the running water sound can get noisy when the water runs at more than 1.5m/s - 15mm can still deliver large amounts of water, it just has to run faster to do it, so anything over 1.5m/s then you start to hear the water running in the pipework. That why if there are high flow outlets with a good mains pressure and flow then increasing the pipe to 22mm will still deliver that flow but at a lower velocity, therefore less noise and friction on the pipework/fittings.