H/C valve shower pressure query

[Deansplit]

Hi

I have a dilemma - I'm installing 2x showers. Originally I was going to go electric but have changed to the H/C water system. My supply is from a pressurised un-vented cylinder.

The facts:
En suite 1 is 6m from the cylinder (a further 3m to the shower), about 1.5m higher and is currently fed with 15mm pipe. En suite 2 is virtually directly below en suite 1 so lower than the cylinder and a similar distance away from it, however, the easiest way to get H/W to it (currently only cold feed) is to tee off after 5m on the 15mm pipe.

My query:
Will 2 showers have adequate power/volume of water (I wanted one to have body jets) or should the feed to en suite 1 be 22mm thereby teeing off from there. There's a big chance both showers will be used at the same time. Or will these need pumps (although I've already posted a Q regarding that - not sure if they made for mains systems?)

Many thanks for any help.

 

[mysteryman]

You need to check that your incoming water main can satisfy all simultaneous demands. The bigger shower may need 22mm pipes. You must take the cold feed to both showers from the balanced pressure cold outlet on the unvented safety kit upstream of the cylinder, and this must be used only for mixers or showers, not cold taps and WCs.

 

[Deansplit]

Re 'balanced pressure cold outlet on the unvented safety kit upstream of the cylinder' - what's this? Does this mean 'after' the pressure relief valve?

 

[mysteryman]

Yes, that is more or less it.

Your installer should know about this.

 

[Deansplit]

Presumable the PRV maintains an even pressure then? Is it essential - I think one shower with thermostatic control tees off before this and shares the same pipes as the WC and sink which you stipulate mustn't happen!??

 

[mysteryman]

They will work much better if installed correctly.

Remember that the limiting factor is the capacity of your cold main.

 

[Deansplit]

Yeah I know - is there any way of finding out(free of charge) what the pressure is? ie. is there such thing as a website which tells of all the pressures?

 

[mysteryman]

You need to measure the flow rate against a back pressure of, say, 2 bar and see if that is as much as the combined shower flow rates plus ...

 

[TicklyT]

I would be tempted to specify one thermostatic and one electric shower, so you have a backup if one system is unavailable for any reason.

 

[Deansplit]

Well, there's 2 other H/C water supply showers in the house so originally these other 2 were to be electric for that reason. Been put off by the fact that the cable isn't larger enough -= a lot of floor lifting let alone 40 quid for the 10mm cable - I already have the elec shower bought! Mmmm, dilemma city! Just also discovered pressure here is 2-3 bar and a 6 jet shwr will struggle? - does that make any odds?

 

[mysteryman]

You still need a good mains supply, however the water is heated.

 

[Deansplit]

is 2-3 bar poor then? Previous showers were all electric - worked fine, but were 7kW as opposed to the 9.8 one I have ready to install (if I decide to!)

 

[mysteryman]

You need to look at your required flow rate and check if your main can supply it.