electric shower

Any advise on the following
Would a shower head controlled by a manual mixer tape supplied by 12kw instant water heater provide the same output as a 12kw electric shower. The instant water heater will also supply a basin tape but not at the same time as the shower
This would save me having to purchase a separate electric shower if the water heater can perform the same as an electric shower

i dont see any reason why it wouldn't

If the heater regulates wtaer temp the same way as a shower does (restricts water flow)
then watts the difference?

did you see what i did there? me so funny

Certainly possible, some of those heaters are designed for that exact purpose.
Check the manufacturers specifications however, as some heaters might not be suitable for that, or they may require the use of a specific type of shower valve.

I agree Flameport. Some instant water heaters need a venting type of tap.

Maybe worth getting advice on the plumbers forum, they aren't that bad!

Just imagining a situation where the temperature regulation is by flow rate, as in many electric showers......

Say your shower head delivers 10 litres per minute, and the heater heats a flow of 10 litres per minute to 50 degrees.

You want to set your mixer to 40 degrees, so you reduce the hot flow to 6 litres per minute by adding 4 LPM of cold water at 20 degrees.

But reducing the flow through the heater increases the temperature of it's output - that' s gone up to 70 degrees - so the temperature at the shower head is now.... 50 degrees

So you tweak the mixer again. The hot flow slows, so the hot temperature goes up to, say, 80 degrees, so the shower temperature is now ..... 50 degrees

One more tweak, and the hot flow is so low, the heater shuts down, and you get a cold shower

If the temperature regulation is done ONLY on flow rate, AND the flow rate through the shower head is fixed, the water temperature is also fixed, because no matter how you tweak the valve, you will always be adding 12 KW of energy to 10 Litres of water, whether you heat all 10 litres a moderate amount, or allow a small trickle of water through the heater and inject superheated steam into the mixer valve to mix with cold water.

purpose built electric showers INCREASE the flow rate to reduce the temperature. Most mixer valves REDUCE the hot flow rate and add cold water to reduce the temperature.

Good point. So in theory you will not be able to reduce the temperature by the mixer tap as you will only be reducing the flow therefore increasing the temperature, if you was to increase the cold water flow at the mixer tap supplied by the same mains pressure/pipe as the hot water, would this reduce the temperature or will it also reduce the hot flow therefore increasing the temperature, or would the temperature remain the same as the increase in the cold flow will counteract the increased heat but reduced flow to the hot

How would the instant hot water systems work that specify they can be used with a shower head, such as caravan installations?

The model I illustrated assumed the temperature was ONLY regulated by flow. If there are other means of regulation in the heater, stabilising the temperature over a range of flow rates, then a mixer will work.

If the water heater manufacturer has taken the cheap 'n' cheerful route to the extreme, and relied solely on the user setting the flow to control the temperature, then the above could occur.

Instantaneous heaters suitable for caravans are more likely to be gas powered, something more akin to a combi boiler with all it's usual control mechanisms.

Electricity supplies to caravans are usually of limited capacity, often no more than 4KW. That would just about support a very low powered version of an instantaneous electric shower.

Instantaneous electric showers usually have just a single cold water feed, and all the water flows through the heater. The temperature control valve regulates the water flow. The faster the flow, the cooler the shower.