Solar Water heater Technical Specifications Inner tank shell is made of SUS3042B food grade stainless steel plates, welded by automatic argon arc. Water is pure and drinkable. Heat insulation of water tanks adopts polyurethane foam, thickness is 55mm. Silicon rings to connect and seal them. The tubes and supports are adjustable, power bearing is average, and can assure the vacuum tubes to use long time. Whole glass vacuum tubes adopt super hard borax and silica glass. Absorb rate: =93%, thermal radiation rate: =6%(100) Resist 25mm hail, using life can last 15 years. Temperature when exposed to sun without water: 250, 2.5hours to boiling if using single tube. If you use electrical appliances to aid heating, to switch off the power supple before bathing. To test the water temperature before using, in order to avoid scalding.