I just recently purchased my first house and we want to make it as energy-efficient as possible.  We don't have a ton of money to spend so will be taking small steps at a time.  One thing that I'm very interested in right now is replacing our standard tank water heater with a tankless, however everything in the house is electric.

They only electric tankless heaters I've found have been small ones to heat enough water for say, the bathroom sink.  Are there whole-house electric tankless heaters, or it that too inefficient?  Should I buckle down and work on replacing the electric with gas first even though it will take a while to save up for that improvement?