The Wattersaver High Efficiency Electric Water Heater by ECR International is designed as a full "drop in" direct replacement for existing 50-gallon electric water heaters, but operates with an EF rating of 2.4, nearly three times as efficiently as a conventional electric water heater. With this gain in efficiency, the WatterSaver pays for itself within two to five years. The WatterSaver residential high efficiency electric water heater can be installed anywhere that a standard electric water heater can be installed. ECR International. Circle 9.