Ecosmart® SMART SPA 5.5 Smart Spa Electric Inline Heater 1 Phase 5.5 kW 220V. Ecosmart Spa Heaters operate by utilizing the latest flow sensor technology instead of the traditional pressure switch activation and contactors to reduce the risk of burned elements, which increases functionality and reliability. The Smart SPA Series comes with a digital thermostat control so you can set the temperature exactly where you want. Ecosmart Spa Heaters are compact and easy to install for a new system or to replace any existing spa heater, including Hayward and Ray-Pak