If we installed a new electric hot water heater would this work safely with the existing boiler? Would it also?

we do the same thin shut off the hot water to save money an it does cut the bill way down. turn up the tepature of the hot water heater so it gets hotter and stays hot longer. we usually turn it on for 15 to an hor when the watr is no longer hot but it wont work if the water temp is low