I know that has been answered a long time ago, but I can't find the thread.

So, please, what is the maximum wattage shower heater I can use?

Thanks.

45A at 220V is 9900 Watts.

We have two 7kW water heaters and 4 aircons on a 15/45, running both heaters and all the A/C (total 22kW) will open the incoming 50A breaker (it's pulling about 100A), but in reality we rarely go anywhere near the limit.

To our OP, 7kW (31A) shouldn't be an issue.

And the next question is... When you are running that new big draw heater at max what is your voltage drop? Depending on the distribution system in your area the voltage drop could be big. If so, be sure to turn of you fancy new air con units and other motor loads when you shower. Except for the poor overheating water pump of course....

Thanks for the answers. I'll probably not be getting the max size water heater, but a bit stronger than the present 3.5 will be nice.

My pal has all the latest gizmos but non work after 5pm, 180 volts.

Nothing wrong with going with the biggest size heater your service allows. I would recommend it actually, I found my 6000W undersized at the peak of some cool seasons. But it would be a good idea to crank on a few of your biggest loads and perform a voltage check at a receptacle. Often in the evening at my place with two A/C units running and half the lights on I could be floating between 195 - 200 V. This will nose dive if I now crank on the biggest water heater. So I now have a routine of turning off all motor loads possible before showering..... until the PEA shows up at my doorstep to save me.....been waiting a couple years now.

Thanks for the contributions. I picked up a 4.5 kw heater on special today, and the MIL will be getting the old 3.5, which is the largest that her meter will allow.

Thanks for the contributions. I picked up a 4.5 kw heater on special today, and the MIL will be getting the old 3.5, which is the largest that her meter will allow.

Is she insured. ...................................

It is not practical if renting, but a big boiler electric hot water system (need hot water plumbing) only draws typically at max about 2000W when it is on, so for some people this is actually a good solution.

Or put in 3 Phase and triple what you get.

Voltage drop and the size of the consumers mains are the important factors. Your voltage on load should not be less than 198VAC max. this is 10% below the nominal 220. the smaller the heater in kW the better, make sure you have good water pressure. A 20A heater is ample for showers, temp set at 60C max.