If this fan goes straight up to the ceiling than you should check where it goes at all. I have seen them ending in the attic instead of ending outside via a special roof tile. This could be against the building regs though I'm not sure about . At least it is idiotic to cover the roof in a vapour barrier and then blowing steam into it. If it does not end in the open then talk to the builder. Not only that cables could oxidise but the timber could start to rot, most modern houses have no treated timber at the inside any more.
The fan could indeed be to weak and the pipe should be insulated, preferable been made of flexible plastic and not of flexible aluminia. You need as well an air entrance for the fresh air going into the in suite to replace the expelled air, usually at the bottom of the door. No fan would manage to blow out air ad infinite if there is a vacuum created.