... non pressure solar system 1.Certificates: CCC,ISO,CE,KEYMAEK 2.lifetime:15 years , guarantee:5 years compact non pressure solar systemWorking ... steel 1.5mm5. insulation layer : polyurethane foam 55 mm 6. heat preservation: 72-80 hours 7. hail resistance: 25mm8 ... . Optional: heat exchanger (red copper), electric heater (1.5kw, 2kw, 2.5kw, 3kw), assistant tank( 5L, 8L, 12L, 15L), magnesium ...