Instantaneous water heater with thermostatic shower?

[PG77]

Hello

I would like to replace my electric immersion water tank with a 12kW instantaneous water heater (for example a Stiebel Eltron DCE-X 10/12 Premium, or similar) to servce kitchen and bathroom (one bed flat, no gas).

I currently have a concealed thermostatic shower (one handle to regulate flow, one handle to regulate hot/cold).

I have read different opinions on whether an instantaneous water heater could work with a thermostatic shower.

I am no expert and don't really know how these systems work, hence could anyone please explain, based on personal experience, why it would or would not work?
What would be the cons?
How do you regulate water temperature? from the heater? or from the shower handle? or both?

Thank you
PG

 

[oldbutnotdead]

If the cylinder is modern (directly insulated rather than those red soft things thrown over it) I'd recommend keeping it.
Reasons- a shower from a 12kw flash heater will range from ok in the summer to a bit rubbish in the winter (when incoming water is colder). Turn the kitchen hot on at the same time and you'll get a chilly shower.
Have a look at your consumer unit. Does it have RCDs or RCBOs in it?
How easy is the cable route from CU to where you're planning to put the flash heater?
Just had a quick look at the specs on that heater you mention. They suggest it will deal with 1 shower OR 1 kitchen sink.
Max delivery rate is 6l per minute of 38° (warm) water.
The 'precise temperature control'- the documents imply that you can precisely set the maximum temperature BUT if your required flow rate is higher than the volume per second that can be heated to that temperature then the maximum temp will not be achieved (so don't think there is internal throttling to maintain temperature).
In short, they are ok if you are desperate. But your existing setup is a better way of delivering hot water.
If the cylinder doesn't have an integral foam insulation jacket, get it replaced with one that does. Modern cylinders hold temperature very well so your dhw energy costs will not be much greater than the bill from your flash heater

 

[PG77]

Hello @oldbutnotdead thank you for your reply. my cylinder is 20 years old I want to get rid of it both because it's old and not functioning well, and also to create space in the flat.

Assuming I am fine with the electrical side of things, what I am trying to understand is whether or not that electric water heater will work with a thermostatic shower (assuming max delivery of 6l/min at 38 is ok for me) or if there are particular cons, because I have read different opinions around this - some say that those heaters would only work with manual showers.

Also apparently the specs say that it works with either 3 basins or shower+basin or shower+kitchen sink so that should be fine. thank you

 

[oldbutnotdead]

Your thermo shower won't function as it does now because the incoming water temperature will be lower. As long as that water heater isn't an open outlet type (which it doesn't appear to be) it will deliver hot water to the shower valve.
Provided cold and hot pressures at the shower valve are similar, the valve will prevent the shower going over temperature (unlikely to happen) but it can only deliver a max temperature of whatever the flash heater is supplying so you'll no longer be able to have a deluge of hot water.
6 litres per minute of lukewarm water isn't very good. Consider- it'll take a minute to get enough warm water in the kitchen sink to wash some plates.
How much useful space is the cylinder and tank occupying? I'd still suggest upgrading the cylinder rather than ditching it.
I have a smaller (3kw) type in the garage. It is absolutely fine for occasional use but as a long term sole supply of hot water would be very irritating

 

[ianmcd]

post pics of your existing HW cylinder and pipework so we can see what your existing set up is

 

[PG77]

Thanks @oldbutnotdead . @ianmcd attached is my setup. I have a loft above, that's where the pipes run. Thank you

 

[ianmcd]

OK so you have an unvented HW cylinder , so a unvented water heater as you suggest will work, but with that rainhead shower that you have you will be extremely dissapointed with the outcome, the flow rate will be extremely poor, I wouldnt advise doing it to be honest, you say you are having problems with the existing cylinder, what exactly is the problem with it ? they are usually pretty reliable and a far better set up than what you are planning to replace it with

 

[PG77]

Thanks, I would easily replace that showerhead with one that would improve the flow - assuming these exist.

I'm also wondering if I could set up two electric units, one for the kitchen one for the bathroom but not sure if these would have electricity implications (eg could they be ran at the same time?)

The current tank doesn't really work (bad insulation) but most of all I want to get rid of it to create space. Also I like to have hot water on demand rather than heating it and storing it as I may not use all that much.

 

[oldbutnotdead]

You'd have to ditch that rainhead showerhead, max flow from a 12kw flash heater will just sort of dribble out of it. The handheld head on the flexi- yes you could swap that easily enough.
No, 2 x 12kw water heaters would be a very bad idea. If both were on at the same time you'll be pulling 100amps- which is probably the maximum your CU is rated at and might be outside the service fuse limits (possibly 60a HRC in there).
The space you are going to win is not in my opinion a reasonable return for losing your current (good quality) shower experience. If you were going to win an extra bedroom then fair enough but you're not.
As I suggested earlier, you'll get much better value for your money by replacing the cylinder with a more modern one with modern standard insulation.
Do you own and occupy the place or are you a tenant or landlord (should have asked this earlier).

 

[Madrab]

Don't do it, as suggested you will extremely disappointed with the outcome, you really will be dancing about the shower trying to get wet. Also the thermovalve will struggle with dealing with such a low inlet temp on the hot side, they really are designed to work properly when mixing reasonable volumes on hot and cold, you couldn't be sure how it would behave. Thermovalves can be tempramental when not working the way they're designed. Not to mention how restrictive that concealed shower may be to flow.

The 12Kw heater is as large as they get without going 3 phase so will put a lot of load onto your CU and will need seriously large cabling to the unit.

The cylinder you have isn't that bad TBH, the Santons are an ok bit of kit, even the old ones.