The pre-heated solar water heater adopted copper coil as the heat exchanger,can supply hot water with high quality, clean water copper coil pre-heat solar water heaterDetailed Specifications:Copper coil: diameter 12mm,thickness 1mm ... :1. The pre-heated solar water heater adopted copper coil as the heat exchanger,(as the copper can purify the water),so it can supply hot water with high quality, clean ...