the only way to get around not storing water is to go for something like a rinnai water heater... but then you will have two boilers, one for hot water, one for CH.(the rinnai can be fitted outside though)
but even a 54kw water heater is not going to do 4 showers at once....
but even a 54kw water heater is not going to do 4 showers at once....