Body Spray Jets - System/Unvented vs Highflow Combi?

[BHI]

Hi y'all,

Advice required for body spray jet flow-rates please... Alas money is not unlimited, but would rather get it right first-time around!

Incoming MCW pressure seems good. Boiler install in loft of 3-bed house to feed kitchen sink, downstairs WC basin, utility room sink and two bathrooms:

- Family - Basin, bath and separate shower (including body jets - see below)
- En-suite - Basin and shower (including body jets - see below)

Shower mixer valves (3/4" inlets / 1/2" outlets) are thermostatic 3-way diverters. Both showers will have:

- Fixed overhead ceiling spray head.
- Hand-held spray head.
- Body jets - which is proving difficult to specify boiler type:
... at 0.5 bar = 4.1 l/min flow rate.
... at 1.0 bar = 5.2 l/min flow rate.

Therefore:

- Best case (if only fit 4 x body jets) at 0.5 bar requires 16.4 l/min flow rate.
- Worst case (if fit all 6 x body jets) at 1.0 bar requires 31.2 l/min flow rate.

Will probably be rare that both showers would be used at the same time.

SO THE BIG QUESTION - system boiler and unvented cylinder, or highflow combi to provide the desired showering experience?!

Many thanks in advance...

 

[Roger Welton]

At 32lmin no combi will do that!

 

[BHI]

That was my concern too Roger when I asked about the flow-rates!

So please forgive my ignorance... But are the body-jets too much for any set-up? (Hence considering only fitting 4 rather than all 6)

Would an un-vented cylinder be able to provide 32 l/min flow-rate?! The basic maths works out at only 6.5 mins from a 210l cylinder or maybe 8mins from a 250l... Although that doesn't take in to account the reheat rate of displacement MCW, etc.

To be honest, I suspect that the jets won't be used that long anyway - more of a rinse off / occasional thing. (But those are the valves we've got, so might as make the most of them...)

 

[dancinplumba]

32lm is for both hot and cold thro shower,
probs more cold than hot

 

[BHI]

Valid point Dancin'...

...especially since thermostatic valves tend to require a hot feed around 50 degrees to work best? So are you suggesting that a balanced hot and cold from the loft could work from a combi too?

Anyone got any personal experience of this? Nervous spending so much money!

 

[dancinplumba]

Valid point Dancin'...

...especially since thermostatic valves tend to require a hot feed around 50 degrees to work best? So are you suggesting that a balanced hot and cold from the loft could work from a combi too?

Anyone got any personal experience of this? Nervous spending so much money!

not sure what you mean hot and cold from the loft ??
but this all depends on incoming supply pressure and flow rate,
there are combis that produce high flow rates try atag boilers.
there are positive and negatives for both systems.
have you considered thermal store ?
but it's all down to flow and pressure
imo

 

[BHI]

Just understood that with a system boiler / unvented cylinder, the incoming MCW needs to be routed up to the boiler in the loft where a pressure balancing valve splits hot and cold domestic feeds?

Haven't looked into thermal stores yet... Will research now! Many thanks.

 

[ecowarm]

You can get that flow rate through a Megaflo HE and the like but only if you have suitable flow rate and pressure on the incoming water main. You would need minimum 3 Bar and 40l/min

 

[NickH]

I would never contemplate a shower with that sort of water usage , its just crazy. If you had 6 jets going (31 litres) and an overhead, say another 15 or so, and you'll be using 46 litres a minutes. Thats just not sustainable except with the biggest water system. You could run out of hot water in minutes.

 

[PlumbBobBob]

i hope you're not on a water meter with that sort of usage would work out rather expensive! i would forget about the body jets and just go for the overhead shower.

 

[Howsie]

Unvented all the way.

Body jets, 6 over kill, four ample, two just fine.