Soldato
Whats a 3kWh heater?
Efficiency is conversion of energy to its use(heat), it's not about heat transfer. Not sure what you are on about with pumping, an immersion heater simply sits, immersed, in water within the tank. Im confused about what you are talking about to be honest if we are talking about a hot water tank with stored hot water. Its not an inline heater.
Exactly I have no idea what hes waffling on about
As you say unless you are converting the 3kwh of energy being consumed by the immersion to some other form of energy/radiation by default its converting that to "heat energy"