Choosing a Water Heating System
The most common type of home water heater is the conventional storage water heater. It ranges in capacity from 20 to 80 gallons of hot water and can operate on a variety of energy sources. This type of system, although the most common, is generally not the most efficient as it continually heats a large quantity of water whether it's needed or not.
There are a number of choices beyond the conventional storage water heater, including demand (tankless) water heaters, heat pumps, solar heaters, and tankless coil and indirect water-heating systems. Choosing the best water-heating system for a home requires an understanding of how each type works and the comparative advantages of one system over another.
Additional information on hot water systems and criteria for selection and purchase is available from the Department of Energy.