Electric tank hot water heaters are actually very efficient, more efficient than gas tank hot water heaters. Gas HW heaters need to be vented and lose heat through the venting process. Electric HW heaters are like giant double-walled thermoses. Once the water gets up to the right temperature, it takes very little electricity to keep it there because the new HW heaters are so well insulated.

Stay away from electric on-demand HW heaters, though.