What size pipe for shower mixer

[Matt K]

Hi there!

First post, so go easy on me. Please could I have some advice? I’m over-thinking something and it seems the type of HW system has a bearing on what size pipe is best for certain applications, so what better place to ask this question than a plumber’s forum?

I have an unvented HW cylinder and system boiler setup and am looking to fit a concealed shower mixer valve in a new en-suite, situated one floor above the boiler and cylinder. The mixer valve takes 3/4 bsp for the H&C inlets, so I would guess I need to use 22mm pipe for these connections? The current bath has been plumbed with 22mm for the H&C feeds.

What do you think, should I use 22mm for the H&C feed to the new mixer valve, or reduce down to 15mm? I have a mild concern I might mess up flow rates for other outlets if I use 22mm for the new shower, is all.

The incoming mains pressure is about 6bar, with a pressure reducer to take it down to about 3bar, and the feed from stop tap up to the cylinder is all in 22mm. Cylinder has a valve to provide a balanced cold, which currently is only plumbed up to the bath tap. I intend to extend the existing hot and balanced cold up to the new en-suite.

Many thanks,

Matt

 

[Ben-gee]

Depends on what flow rate you want out of this shower and wether or not that is required when multiple outlets are in use.
A “normal” shower eg bar valve, hose, handset can usually only provide 15l/m in which case 15mm hot/cold is probably fine.
I have just fitted a high flow concealed valve that can handle 35l/m , and so that is piped in 22mm. (However at present it only runs a hose outlet of 16 l/m, but possibly an overhead will be added later...)

 

[steadyon]

I'd go with 22 mm:
1. It's in keeping with the 3/4" BSP inlets.
2. If you ever wanted to install a shower with a higher flow rate you should be able to avoid changing the pipes.
3. The flow rate is most likely to be determined by the shower, so using 22 mm shouldn't starve other outlets.

 

[Matt K]

Thank you very much, Ben Gee and Steadyon,

So far, I think I’m swayed by Steadyon’s recommendation of using 22mm. However, I am still drawn to Ben Gee’s recommendation - after all, it is only a ‘normal’ shower (single outlet mixer valve, running to a riser rail that has a diverter for supplying either a handset or monsoon head) and the outlet of the mixer valve is 1/2” BSP, so it will only run in 15mm between the valve and the shower rail. Can’t find any tech specs that say what the max flow rate is, though.

Sorry, I should have mentioned that before.

I shall go get the necessary parts for running it in 22mm, then.

Thank you again,

Matt