... solar energy,and heats the water inside the tube,hot water rises,cold water flows down). It ... inner tank. The hot water rises from the tube into the tank, and heats the copper coil ... with a copper coil inside),the three-high vacuum tube,bracketoptional parts:A controller----show water level, temparature ... /AL Number of the vacuum tube availabe for your choice: 18,20,24,30,36.Tube size: diamter: 47mm, 58mm ...