With copper coil heat exchanger,passed EN12976 performance testing,more than 2.5M2 heat exchanger area,5 years warranty Specifactions of close loop Pre-heating solar water heater1, Main tank is non-pressure, Inter copper coil can bear 6~8bar work pressure.2. The material of inner tank is SUS304 2B food grade stainless steel with 0.4mm thickness.3. The material of outer tank is SUS304 stainless ...