Replumbing Whole House and Flow Rates
Drainage and wastage systems and plumbing help, advice and answers

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Joined: Sun Nov 10, 2019 7:54 am

Replumbing Whole House and Flow Rates

by Stripee » Tue Dec 10, 2019 2:46 pm

Here's the situation: we're mid-renovation of a late 50's ex-council house. We've had various work done so far mostly upstairs, with downstairs scheduled for spring.

Work done includes:
+ new water mains connection from the street, previously lead, shared supply (25mm mdpe to new main stop cock at the downstairs bathroom at the back of the house).
+ new worcester bosch 38cdi classic combi in utility
+ new rads, keeping some of original pipework. Heating working well.
+ upstairs hot/cold replaced with John Guest speedfit with as many swept bends as possible.

outlets do / will comprise of:

Upstairs bathroom
basin with mixer tap
combined thermostatic bath filler / shower mixer

Downstairs bathroom
basin with mixer tap
electric shower

washing machine

Other info
+ H/C supply runs up to the loft with end caps for potential future loft conversion
+ there's still a fair amount of unknown original hot/cold pipework downstairs behind tiles and boards from various eras which we plan to replace with new JG speedfit.
+ Mains enters at the bathroom and feeds through to the rest of the house via some unknown pipework behind walls and tiles which become a "known" in the new year.
+ 1x Outside tap @ rear.
+ May also add an outside tap @ front.
+ boiler feed & outlet is all 15mm.
+ Spec of the boiler hot flow rate capacity is 14l/
+ Our builder set us up with 22mm cold feed which currently is fed via the old "unknown" probably 15mm copper pipework hidden behind the downstairs bathroom walls.
+ the upstairs bath, basin and kitchen sink currently are supplied by 15mm JG which spurs off the main 22mm pipe
+ Current COLD flow rates at the garden and original kitchen tap are coming out about 18-20l/ min
+ Current HOT flow rate is a feeble 6l/min ish from the same kitchen tap.

Clearly this hot flow rate isn't right. I'm pretty confident it's not the boiler at fault, but something to do with the existing pipework set up. we won't know for sure until we rip out old bathroom to reveal existing pipework. It has been suggested by someone that the 22mm is causing the system to be unbalanced and everything should be in 15mm.

The question
I fear this may be an age-old question.... in order to optimise flow rates, should we have 15mm hot & cold throughout the house or combine multiple diameters (eg 22mm cold feed, 10mm for toilets & Washing machine etc)? What does a perfect "balanced" system look like? I've yet to find an "industry standard" for what constitutes an ideal combi set-up, but have equally discovered there's quite a bit of "opinion" on the interweb. Worcester Bosch technical advice line were helpful to a point, but i didn't get the definitive answer i was hoping for.

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