This International Standard specifies definitions and test methods for durability and performance of heat-pipes for solar thermal application. This standard is applicable to all heat-pipes for use with evacuated tubes, including glass-metal sealed evacuated tubes and double-glass evacuated tubes, as well as with flat plate collectors. This standard provides test methods for determining durability of the heat-pipe, including high temperature resistance and freeze resistance. This standard also provides test methods for measuring performance of the heat-pipe, including starting temperature, temperature uniformity and heat transfer capacity of the heat-pipe. This standard is only applicable to gravity heat-pipes.