15 mm supply to 22 mm for shower/bath combination

[nickbot]

Apologies if this has been addressed previously (long time lurker, first time poster!)

I'm currently replacing a shower cubicle with a bath/shower combination, using a thermostatic bath/shower valve and bath filler (from bathstore), all of which use 3/4 BSP fittings. I know it may split opinion, but I'm intending to use plastic pipe and speedfit fittings (perhaps compression behind stud walls), but this is not the direct focus of my query. It seems that for 3/4 BSP fittings, the standard "interface" is 22 mm diameter (i.e. from Google searches, no 15 mm to 3/4 BSP seem to exist).

Currently, the shower (now removed and capped off) is fed by hot and cold 15 mm dia copper pipework. I know there are "22 mm to 15 mm reducers" available from Speedfit (and others), but I would be using these as a 15 mm to 22 mm "increaser" if you see what i mean! I know that physically there should be no issue in using such hardware to join 15 mm Cu pipe to 22 mm plastic pipe, but I was just wondering if there are any issues (pressure/flow drop perhaps?) in taking a 15 mm hot/cold supply and increasing it to 22 mm dia to use for a shower and bath?

Many thanks in advance for any help anyone can offer, and thank you retrospectively for such a useful forum!

 

[swbjackson]

IT depends on your water source. If mains fed 15 will be fine. If cistern fed you will get a reduced flow rate.

 

[swbjackson]

You can get 15 x 3/4 speedfit tap connectors.

 

[david17uk]

If you've got a combi boiler it will work fine.

If you've got a cylinder it should really be in 22mm pipe.

 

[nickbot]

Thanks for your help so far guys...

The source is an unvented hot water system, so hopefully the pressure should be adequate (states 3.5 bar operating pressure). The shower valve requires a 3/4 BSP (non taper) male threaded fitting (i.e. the valve has 3/4 female threaded ports) and I haven't had any luck in finding such a fitting with a 15 mm input,...I'm therefore inclined to go for 22 mm throughout after the 15 mm Cu pipe comes up through the floor - hope this is ok!

 

[swbjackson]

Go to www.bes.co.uk

Item number 6577 will convert to male thread and then item 7088 15 x 3/4 speedfit tap connector.

 

[tincup]

Hi


screwfix do this Quote No: 82086
http://www.screwfix.com/prods/82086/Plumbing/Compression-Fittings/Flowflex-Male-Coupler-15mm-x#

HTH

 

[nickbot]

Many thanks once again guys

So, in your opinion, should I stick with 15 mm pipe throughout (now that sourcing of fittings isn't a problem thanks to the links supplied)?

 

[david17uk]

15mm pipe will work, you'll just have a slower flow rate.

 

[nickbot]

15mm pipe will work, you'll just have a slower flow rate.

Thanks david17uk, that's got me thinking that 22 mm is perhaps the way forward, but the source supply into the bathroom is still 15 mm, so whilst the flow will be increased by increasing pipe diameter to 22 mm, the pressure will drop I presume? I'm hoping on my 3.5 bar system that pressure won't be a big issue (fingers crossed!)

 

[david17uk]

You can't change pressure by changing pipe size.

It always confuses people - pipe size can only change flow rate.