Lordshandyman, If I remember correctly, if your running 110 volts to the hot water element, your only using about half the watts, as the rating on it.
If you didn't take that into account, then your using even less electric then you thought...


Here's a video of what some folks are doing with hot water heating elements. Some are even using stainless steel elements...
http://www.youtube.com/watch?v=_DMiYSoffBA