Solar water heater with SOLAR KEYMARK,ISO,CE,SGS - Automatically controlled - Highly efficient insulation with polyurethane low pressure olar water heaterMaterial:Inner tank: stainless steel SUS304/2B, δ0.41mmOuter tank: galvanized/color ... - Can be used together with auxiliary electric device or gas heater- Long service life, can be used as long as 15 years low pressure solar water heater