Solar hot water heater, 30m copper coil inside of tank, which could bear high hydraulic pressure. specification ... Vacuum tube: Tri-elements coating, 58mm×18m.Accessories: Water auto-feeding tank, electrical heater. Copper coiler: For heating exchanging, Ø12mm×30m, ... you will enjoy more fresh and high hydraulic hot water out from the coiler. Solar hot water heater& 30M copper coil for heat exchange