Electric shower available as 9.5kW or 10.8kW

They are the same 0.185 ohm resistive element. The 10.5kW one is rated at 240V supply and the 9.5kW one at 230V supply.

What you actually get out of it will entirely depend on your supply voltage at the meter and the resistance of the the cable that supplies the shower.

Thought they had to assume 230V now?

They also come in multiple versions at different wattages, eg:

- see p4:

The nameplate rating is for 240V, but the instructions say what you get at

(UK electric showers aren't sold in countries where the voltage is actually

Yes, it's possible your supply could cope with a 7.5kW shower (32A MCB required) where a 9.5kW (needs 40A) or 10.5kW (needs 45A) might exceed the diversity calculation. eg if you were on a 60A supply then 45A would eat most of your current capacity. If you had say storage heaters on together you could trip the supply.

Theo

Do upou think the kW ratings may simply be the Imperial equivalents of some esoteric SI values (in integers)?

PS: My advice is to buy the lower-rated item so that you are less likely to have to get out of a tripped-out shower, hurriedly get partially dried and dressed and get down to the garage to reset the consumer unit before continuing with that hot shower.

No. They're the highest ratings that can be achieved with a given MCB: (within tolerance)

If the electrics are correctly designed you should never trip the MCB. Doing so is a faulty installation.

Electric showers are weedy at the best of times, so higher is better. However it also depends on your water flow rate - if you're fitting a dumb shower in a low flow situation, dumping 10.8kW into a trickle of water could be uncomfortably hot. The dumb showers don't modulate, they just have two heating coils and you turn on 0/1/2 coils and then throttle the water flow to set the temperature. If the full-bore water flow is too low such that 2 coils makes the water too hot, you can only use one coil and the second coil is wasted.

So it's better to size them based on the measured flow rate, although that needs the manufacturer to publish the temperature/flow curve. Or find a 'digital' (non-mixer) shower with proper modulation (ie a big dimmer circuit for the heating coil), which will avoid throttling the flow rate too.

Theo

Since I am spoilt with a power shower, I would suggest get the highest rated item that is compatible with the current house wiring sizes and MCB rating.

YMMV

Oh dear. I see you have unilaterally repealed Ohm's law.

Only Ed Milliband is allowed to do that.

'Hot' shower from an instant electric shower in mid-winter ?

I'm not sure how any Imperial unit could come into play in this matter.

We used to have a Mira - I think a 10.8kW- and it would give a hot shower in winter.

I a previous house, we’d had another make - I don’t recall - but 7 kW. That could disappoint in cold weather and was sensitive to variations in supply. If the flow to it dropped, it cut power to the heater and you got a cold blast.

The Mira seemed immune to this.

We now have pumped ‘power’ showers. Better as showers go but you need to heat a tank of water.

My advice would be don't bother with an electric shower! :-)

However if you must, fit the biggest most powerful you can get away with, and install appropriate circuit protection and cabling so that tripping is never a consideration.

Yup.... so long as you are happy with 4 lpm!

That would draw nearly 1,300A, and give you a >300kW shower.

We have a 10.8 kW shower, but I always run it on the 'intermediate' power setting - except perhaps during an extended sub-zero period of weather lasting for a week or more.

I do that because I don't like the 'tropical deluge' my wife insists on. A modest flow of water is enough to get wet and doesn't involve flooding the bathroom[1].

What do you mean?

Watts and kilowatts are Imperial measure, surely?

My bad, wrong units. That's the conductance 0.185 Siemens.

Should be 5.4 ohms.

Probably, and the Imperial watt = the SI watt.

Indeed.

Nothing beats a tankful of hot water at 60°C plus thermostatic mixer for a shower