If you are going to have 2 electric showers you will need to have them "interlocked" at the consumer unit - this is to prevent both showers being in use at the same time. Each shower could be 9.5 or 10 kW each which means that if both are on at the same time, they would overload the supply coming into your house.
But are you really talking about 2 electric showers? You mentioned a combi boiler - is the existing shower supplied with hot water from a hot water cylinder - in which case it is just a mechanical mixer and not electrical at all.
J, March 2008
