The Eco 11 is designed to heat up to 2 gallons per minute and is optimal for the weather of 67 F and above. When sized correctly your tankless water heater will provide you with endless on-demand hot water - rather than storing it like a tank-type water heating unit. It's compact and wall-mounted so you save valuable storage space for your new closet! Ecosmart tanks only turn on when you need warm water, saving you up t to 50% in water heat loss. They are also the only electric. Eco 8 is one of the smallest electric tankless water heaters from EcoSmart. It can handle one sink in colder climates, and up to 1 shower and 1 sink simultaneously in warm weather. The 18 is the mid-range model that can heat over 2.5 gallons per minute. A higher range unit that heats 3 psi can handle 2 showers simultaneously without running out of hot water. This unit is designed for use in hot or cold environments.