Open loop water heater 1. 5years warranty 2. CE,SRCC,SGS,Solar Keymark,ISO9001:2008 Open loop water heater features:1. Stable and reliable perfor mance,well resistance2. Easy plug-in installation3. Economical goods4. The life of the vacuum tubes is 15 years5. Anti-freeze-55 degrees.6. Resists 25mm hail