Water heater capacity is the number of gallons the electric water heater holds in a storage tank for future use in the household.
Finding the Gallon Capacity
On the side of the water heater, there is a tag that will indicate the number of gallons in the heater. This is the capacity of hot water the tank holds. If you are unable to locate this tag on the side of the heater, look in the owner's manual that came with the tank.
Hot water tanks generally run in sizes of 40, 50, 65 and 80 gallons. Smaller tanks are used for apartments or small condominiums, and medium to larger size tanks are used in duplexes and homes. Extremely large hot water tanks of 100 to 120 gallons are more often installed in older apartment complexes or dormitories.
Tankless Water Heaters
An alternative is the tankless water heater, also called a “hot water on demand” system. This type is considered a more eco-friendly alternative because it does not constantly use power to heat stored water. Instead, it heats the water as needed and as it flows through the tank.
Hot water is measured in amounts of water heated per minute or gallons per minute. Commonly, tanks are installed in several locations around a residence where hot water would typically be needed, including the kitchen, bathrooms and laundry room.