Just to note that that can be deceptive, heaters arn't on all the time, only when the temperature drops to a certain point then it kicks in and then turns off when the water reaches a certain temperature. Though with the weather we are having now I'm noticing mine is on more often than not .
agree with the other up there. it would also use 0.1 amps if your in the UK as long as the heater is on. It might be a little more however due to the neon. which ever way it wont cost much to use