A water heater is typically the third largest consumer of energy in the home, accounting for about 13 percent of the gas, electric, or oil bill. New hot water heaters, particularly the on-demand type , are much more efficient than the older tank types - and even those have improved greatly in recent years, but hot water heaters last 10 to 15 years so you may still get to spend a lot more expensive time with yours. According to the U.S. Department of Energy, if you aren't in the market to buy...