Solar engineering 1. Unpressurized 2. 5 years warrnaty 3. CE,SRCC,SGS,Solar Keymark ISO9001:2008 Solar engineering features1. Pressure:Unpressurized2. Heating system: Thermosyphon(Passive)3. OEM&ODM4. 5 years warrnaty5. CE,SRCC,SGS,Solar Keymark ISO9001:2008 This working principle of solar water heater is make it natural circulation between the water tank and the collector pipe