Water heaters are commonly measured by the volume of water they're capable of holding. In the United States this is based on gallons, while the measurement is given in liters in other parts of the world.
Other measurements include the width, height, depth and the recovery rate of the unit. The recovery rate of a water heater is defined as the volume of water it is capable of heating to a target temperature within a period of one hour. It's common to find 40 to 50 gallon water heaters in a three-bedroom, two-bathroom home, though larger units are available. When shopping, consumers may also consider fuel types and configurations, such as tankless water heaters or those that rely on natural gas or solar energy to heat water instead of electricity. Finally, it's also important to consider energy efficiency, which is often provided as a rating from a third party organization. These ratings give information regarding the costs associated with operating the water heater annually. The rating is an estimate based on averages, and the final cost depends on the cost per kilowatt-hour charged by a municipal utility provider and the volume of use that a particular unit sees after installation.