Shower supply where hot and cold are at different pressures

[mikesdiy]

I am not mad keen about having electric boxes in my shower and am looking for options to replace the electric shower which currently runs solely of the main cold feed.

The room does have a supply of hot water that runs from a conventional gravity hotwater tank with a header tank that will be 3+ meters above the shower height. Unfortunately it would be quite difficult to lay in a new cold water feed from the same header as it is a very old house with very thick stone walls.

I would really like to find some way to combine the existing hot and cold (which are at different pressure) in a thermostatic mixer and feed the shower that way. All the common place mixers I have seen do not seem to cater for this, has anybody got any good suggestions as to how I might do this without spending a fortune? Appreciate any good ideas - Mike

 

[chrishutt]

There is still one venturi shower on the market, the Jetstream by New Team, but it looks a bit weird. They're designed to work on cold mains and tank fed hot, although your hot pressure may be too high for it. Try Screwfix for a good price on it.

Otherwise you are looking at mixing tank fed hot with mains cold in a thermostatic shower valve which can work if the ratio between the pressures isn't too great and the cold flow is reasonably steady. I think many shower valve manufacturers specify up to 6:1 in which case if your hot is at 5 metres head your cold could be up to 3 Bar! You could easily improve the balance by fitting a Pressure Reducing Valve (PRV) on the cold supply.

You may also need to fit check valves to comply with water regulations. Mixing tank fed and mains supplies isn't really approved so you need to speak to the shower manufacturer to see what they say about it and whether they will honour their guarantee in such a case. No doubt others on this forum will say you shouldn't do it, but in your situation it may be the only practical alternative to an electric shower.

 

[Expertboy]

Yep you shouldn't do it

 

[chrishutt]

Would you like to expand on that? Why not?

 

[mikesdiy]

Chris, many thanks for your suggestions; I had never heard of the venturi system, I see the add for that now and will follow that up. As a parellel action though I would like to also look at this option of a PRV as this will possibly give me greater flexibility. I dont see anybody selling these, where can I see these so that I can find out about capability, costs etc.

Not sure the regulation thing will apply in my case as the water supply is my own, the main cold is actually Well water that is fed down to a couple of large storage tanks on a hillside some tens of meters above my house, the presure is rock solid stable but will be fairly high compared to the hot which is fed from a header tank in a loft. Whatever I do though it clearly has to work reliably and safely.

Thanks again - Mike

 

[chrishutt]

Try BES for PRVs and stuff. 5 metres head will give you a good shower, but if you want something more powerful you could consider pumping the hot supply to come closer to the cold water pressure.