vacuum tube solar water heater color steel CCC,CE,SGS,ISO9001,Solar Keymark OEM service vacuum tube solar water heaterCCC,CE,SGS,ISO9001,Solar KeymarkInner tank ... system is non-pressurized, water flow depending on gravity water head.This system matched with vacuum tube solar collector. Water flow inside and complete ... given pressure, which is how the name comes from. vacuum tube solar water heater