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I am currently renting a flat, which prevents me from making modification to the walls. However, I still would like to run ethernet cables between rooms. Between all the rooms, there are AC vents connecting them together. Assuming that the ducts are simple air ducts without any moving parts inside (need to check), would a normal ethernet cable "survive" the conditions? I think the maximum air temperature would not exceed 60 degrees celsius.
Lastly, the the building is located in Spain.