... -pressure solar water heaterWorking Principle:Compact Non-pressure Solar Water Heater relies on desity of the water, cold water down, ... plate3. Heat preservation: 55mm,60mm imported PU4. Vacuum tube: single target vacuum tube, coating: AL/N/AL, or Three-target ... sheet or strip8. Daily efficiency: above 50%9. Optional electrical heater: 1.5kw/2kw/3KW10. Heat Preservation: 72hours11. Hail resistance: ...