... the same as water at sea level, 0oC (32oF). Because the heat pipe is located within ... 14oF) will not cause the heat pipe to freeze. Plain water heat pipes will be damaged by repeated ... pcs / 3 pairs8 pcs / 4 pairsHeat pipe Specification: Item No.SpecificationDiameter of solar tubeLength of ... Collector Tube with Heat Pipe (SOLAR WATER HEATER,ISO9001,SOLAR KEYMARK,CE,SRCC,EN12975)