Tankless or on demand hot water heaters are not quite the boon they have been promoted to be. While they will reduce the amount of energy required to heat a given amount of water by 10 to 30 percent (depending to a certain extent on the age of your existing tank model and the efficiency of the tankless unit), there are several big drawbacks to the product. As we said earlier, they are more expensive than traditional hot water heaters, but are still competitive. The difference between tank and tankless...