The E55R works differently than other water heaters because you’re not consuming the 55 gallons of water stored in the tank. Instead, this “static water” acts as heat storage. When you draw hot water, the domestic water is run through the heat exchanger, where the heat from the water in the storage tank is instantly transferred to the domestic water, giving you hot water from the tap.
The tank is only filled once—during the unit’s initial installation—and the water remains in there throughout the life of the water heater. And because it’s built of polymer composite, scale cannot form inside the tank. This increases the life of the tank by decades as well as extending the life of other key components like the heating elements.