... bathing 8) Meeting the demand of well-to-do familiesType: Evacuated TubePressure: UnpressurizedCirculation Type: Direct / Open Loop (Active)Heating System: Thermosyphon ... and stable, easy to install.Tube quantity is optional, from 24 tubes to 36 tubes. solar water heater(SRCC,SOLAR KEY MARK,CE,ISO9001,CCC)