... 0.31mm5,Insulation:foaming polyurethane thickness:50mm or 55mm6,Optional electric heater:220v-240v 1500w/3000w7,frame material :202 stainless steel8, ... the vacuum tube2,The hot water rise in the top of the water tank ,and the cold water sink to bottom,then heat ... valve will open its valve,the tap water flow in the tank ,if the water is full,it will close the valve automatically solar water heater