Instant electric water heater for shower and sink

22 Jan 2011
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United Kingdom
Without boring you with all the details I do not have a hot water boiler or hot water tank in my house and I don't intend to install either.

I have an electric shower in the bathroom (which needs replacing) and a boiling water tap in the kitchen. The only thing I am missing at the moment is hot water in the bathroom sink.

My original intention was to install a small in-line instant water heater under the sink to provide enough warm water for washing hands, shaving etc.

Then I thought as the shower needs replacing why not replace it with a bigger instant hot water heater and use it to supply both the shower and bathroom sink?

Is this a stupid idea or am I on to something?

The shower has it's own 40A CB in the consumer unit. There is space to install the heater in the wall behind the shower (and use the shower electric and water supply). I would have to install a mixer valve in the shower of course. And there probably wouldn't be enough flow to use the sink and shower at the same time which I'm not concerned about.
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Only thing you can do is put a long hose on the shower and use it to fill the basin... which defies regs BTW! :LOL:
Won't keep up the supply for a shower
Why wouldn't it? An electric shower is just an instant hot water heater with a shower head on the end.

I'm looking at this one at the moment: It specifically says it can supply a shower and bathroom sink. Bizarrely it says it is not for kitchen sinks or baths. I can only assume they don't want to guarantee it to supply large volumes. I'm pretty sure a shower uses as much water, probably more, the a full kitchen sink.
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You might get away with an in-line instantaneous water heater around 9.5kW although the shower performance is going to be very limited.

You wiring may need to be upgraded though.

Link to 10.8kW - definitely need to upgrade your circuit -

Why would a 9.5kw water heater be limited in its performance but a 9.5kw shower not? The shower and the water heater are the same thing inside. Yes the flow rate needed for the shower is lower but the water heater is going to supply a flow rate the same as the shower. So there's no difference?

No wiring upgrade required. The supply needed for a 9.5kw heater is the same as for a 9.5kw shower.
Not at all helpful, but when my boiler was broken, I often used my shower to fill up my sink, was just as quick as turning the tap on.
Out of interest I just tested my current shower and it supplied 3L in 1 minute. I suspect that is on the lower side of normal (I'm on a private water supply, the pressure varies, the pressure is low at the moment, I suspect I'd get a higher flow rate when the pump recharges, yes I do know the difference between pressure and flow!). I couldn't measure the temperature but I suspect it is about 41 degrees because it's one of those safe showers deigned for commercial use and is limited to 41.

The Redring heater I posted is rated to supply 4L/m at 39 degrees.
Why would a 9.5kw water heater be limited in its performance but a 9.5kw shower not?

They're both limited in terms of flow and temperature rise but you may be satisfied with the performance. If you're happy with a shower delivering 3-4 l/min then you may well be satisfied with the performance of an instant water heater.

39 degrees
That may be the temperature at the head - it will cool significantly as it becomes individual droplets.

No wiring upgrade required.
Assuming it's to spec at the moment then no upgrade needed - hopefully it's on an RCD protected circuit.

If you are currently satisfied with the performance of your current shower then there's no reason that you won't be able to install an instantaneous water heater.
As most of the above comments- 9.5kw heater will give you a tolerable shower rather than one you'll happpily spend 10 minutes under. It'll do the bathroom sink all right as well (but not at the same time as someone is having a shower)!
Advantage of going that route as well is it becomes non-notifiable work (you're not installing electrical items in a special location) as long as you pay attention to the requirements (cable size, cable installation method, safe zones, RCD protection on any new buried cable)
Unvented, believe that needs a g3 ticket to install so not a diy job
Okay thanks.
I'm surprised 9kw showers are only seen as tolerable or limited. I've never had any complaints with those I have used - including the one currently installed in my house.

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