I've been trying to find an answer to this problem for over 2 weeks now.
Here is the situation:
2 newly installed panasonic 80 cfm bathroom exhaust fans(the kind that fit in a 2x4 joist space) in two different bathrooms. These fans have their own internal flapper.
Bathroom 1: 8 x 4 x 8 Bathroom 2: 8 x 5 x 8
I'm using 3" sheet meal ducting(the kind you have to "snap" together) going horizontally out the side walls instead of going straight out the roof. They duct out to exhaust hoods which also have a flapper on them. I also have put insulation on the whole duct run.(not tried putting insulation on the fan housing yet due to mold concerns.) The duct runs are about 4' each from the exhaust fan and slope downward from the start of exhaust fan to the wall, so you would think condensation would just drip out towards the wall. You can go outside while the fan is running and seems like its pushing out plently of air. The fans are mounted in between the shower and the vanity right above the toilet. The are mounted at a downward angle since the sheetrock ceiling has a downward shape that matches my open beam ceiling slope patter. My whole house is all open bean ceilings, there is no attic. The duct run is made above newly installed sheetrock and the open beam ceilings, with a 4" space between the sheetrock and the open beam ceiling. My open beam ceilings are vaulted going downward towards the side wall, so the ducting runs down the similar open beam downward slope. The ducting is not bent at all in the larger of the bathrooms, and has a slight bend in the smaller of the two bathrooms going out the side wall. When I take a shower in the smaller of the two bathrooms, after about 5-6 minutes, condensation starts leaking from the fan housing thru the grille. I thought it was due to it being pretty cold outside, but today was fairly warmer and the same results happended. In the larger of the two bathrooms, it takes slightly longer to condensate when taking a hot shower since its a bigger room, but it happens in that bathroom as well.
Can anyone shed some light as to how I should go about solving this issue, as I am out of ideas.