Water is condensing in the tubing connecting my bathroom exhaust fan to the roof outlet. This happens in the winter when it is cold in the attic. The length of tubing is only about 3 feet long going through the attic, but water condenses in it, runs down into the fan and soaks into the ceiling sheetrock creating an ugly mess. I have not been able to find insulated tubing so am not sure what to do to solve the problem.