New bath/mixer shower pipe sizes?

26 Jul 2005
Reaction score
United Kingdom
Will be installing a new bath and mixer shower (currently have just an electric shower in a cubicle).

Just want to know whether it is best to plumb in 22mm copper pipe to bath and mixer with 15mm branch to wash basin or just go for 15mm throughout. Will I get better pressure/flow with 22mm or will it not make any difference?

What are connections on an average thermostatic mixer - 15mm, 22mm, 1/2" or 3/4"? And what about for bath taps?

Thanks in advance
Sponsored Links
FOr gravity supplies use 22mm, if it's a combi then 15mm.
Bath taps are 3/4", basin 1/2", though basin mixers can have flexy tails.

Shower mixers can be either size, or even compression nuts for 15mm which looks horrible (eg new Bristan)

Remember all the shower water shares the hose, so no point going overboard about big pipes.
Thanks ChrisR.

I actually have a DPS GXV thermal store/heat bank. This gives me mains pressure hot water, so effectively both CW and HW will be at mains pressure. From your reply I take it that 22mm would be overkill for the shower (since it all has to go through the shower hose - good point!). What about the bath though? Should I use 22mm if they are separate taps and 15mm if it is a mixer?

Depends what you're connecting to as much as anything - the bath tap/mixer will be 3/4". If it's a long way there would be some advantage in using 22mm pipe, but not much. No harm using 22mm if that's what's there already. 22mm Speedfit/Hepworth plastic pipe and fittings is easy to use if you don't try to bend it much. Better than braided flexies.
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local