From the United States of America? - Checkout our specific plumbing forum for you:USA Plumbing Forum

Discuss Bathroom plumbing advice - secondary hot circuit in the Plumbing Forum | Plumbing Advice area at

Afternoon all.

After a bit of advice/guidance.

I'm currently refurbing my 1st-floor bathroom and the ancient plumbing system in the house whilst I'm at it.

It'll have a shower, toilet, basin and a standard size bath. I'm planning a secondary circuit (in copper) for hot water (22mm in and a 15mm return) as currently, it takes around a minute to reach the bathroom in the loft and nearly as long to reach the bathroom I'm refurbing.

There is a loft bathroom directly above, currently fed (using JG) by tee-ing into existing 15mm (both hot and cold) off a mish-mash of 15 & 22 + a bit of galvanized steel which I'm going to replace - the mish-mash that is (not the PEX feeding the loft bathroom).

I'm currently on a combi with 15mm hot outlet, but this is soon to be replaced with an unvented system with a 28 or 32mm feed from the street, into 22mm - pressure into the property is 3bar, current flow rate around 14lt per min.

I'm planning on building 2 copper manifolds for hot and cold with isolators to serve the refurb bathroom and loft bathroom using 22mm copper and taking 15mm branches (in PEX) 1 for the shower, 1 toilet, 1 basin and 1 for the loft for the cold and 22mm off the manifold in PEX to the bath.

The second manifold (again in 22mm) for the hot, 1 shower, 1 basin, 1 for loft and again feed the (standard size) bath off that in 22mm PEX and return from the manifold to the cylinder in 15mm copper.

My question is: Am I wasting my time running to the bath in 22, would 15mm PEX off the manifolds be sufficient? I'm not bothered about a few quid saved given what it's costing I just don't want to waste the pipe/money/effort if I'm not going to fill the bath any quicker!

Also, am I wasting effort with the secondary hot water given that I will be reducing the length of pipe runs significantly? They'll probably be around 7 metres to the refurbed bathroom and around 12 to the loft bathroom. Hope that makes sense!

Shout if you've any questions.

cheers, Chris


Staff member
S. Mod
Gas Engineer
22mm if your planning on doing a return loop else it’s 15mm to save wastage of water

secondary return loop is a good idea but needs to be done correctly eg timer or pir


@ShaunCorbs - thanks for the reply - much appreciated. Was considering return loop, was planning on using a PIR if I go that route.

cheers, Chris

Reply to Bathroom plumbing advice - secondary hot circuit in the Plumbing Forum | Plumbing Advice area at Plumbing questions, answers, tips and tricks.

uHeat Forum Sponsor - - Electric and Water Underfloor Heating Systems
This official sponsor may provide discounts for members

Plumbing and Plumbers

Plumbing Workwear

Shower Power Booster

Plumbase Spares - Plumbing Supplies and Spare Parts

Water Underfloor Heating

CORGI Direct for Plumbers

The Wetroom Store

Plumbase Spares

New Posts Threads Members