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Bathroom vent fans must be vented to the out of doors. Venting this fan into the attic is simply asking for problems. The excessive moisture will cause condensation on the roof members, insulation and eventually cause mold.
Considering this, do exhaust fans need to be ducted?
To put it simply, if you have a colourbond, flat or narrow pitched roof or sarking (silver paper insulation) in your ceiling space then you will need to have a 'ducted' exhaust unit installed. The recommended air flow rate of exhaust fans state they should be between 50 – 100L/s.
Similarly one may ask, how much does it cost to vent a bathroom fan outside?
Cost to Install Bathroom Exhaust Fan Through Roof A bathroom exhaust fan costs between $15 and $300. With labor, expect to pay $60 on the low end and $500 on the high end. This cost depends on the fan price and the project difficulty. You can also redirect air and moisture outside with a roof vent.
To prevent condensation from happening, it's best to insulate the outside of the pipe. I'd give serious consideration to using foam core PVC pipe as the vent pipe for your fan. The fittings can be glued and any water that might form in the pipe will never leak onto your ceiling or down a wall.