I'm remodeling my 10 year old bathroom. The current bath fan is undersized and is vented about 18' to vent in ventilated soffit over the attached garage. There is a water stain in garage where the vent goes out. I want to install a110cfm fan to replace the 70cfm. The 110cfm has a 6"vent pipe where the old 1 was 4". I can vent to the roof thru the attic which about 12' vertical rise. What would be the best vent pipe to use to prevent any condensation in the attic or the pipe? THanks.