Leaking bathroom fan...nothing fixes it!!!
We have installed a new Nutone 80 cfm bathroom fan in our 7'x10' bathroom. We used solid ducting to vent it out the roof with an flappered roof vent made for bathroom fans. We started with a 90 degree elbow, added about 2' of straight ducting and then used about a 30 degree turn to hook into the roof vent. All seams were taped shut. There are two doors to the room. One door has about .25" gap under it and the other has about .5" gap.
The first time we used it, it dripped onto the floor after 5 minutes in the shower. It only drips when we run the shower.
1. We thought there wasn't enough insulation, so we added more blown-in insulation on top and throughout our attic. We insulated the ducting and the housing (10" on top of the housing), R-7 around the ducting. Its about 55 degrees today, but it doesn't seem to make a difference how cold or hot the temperature is outside. Still drips! We removed the blower assembly to see that water was collecting on the top and side of the housing, running down the sides (including over the electric plugs) and onto the floor. It was actually fairly dry inside the ducting.
2. So, we got a 110cfm assembly to go into the same housing, as suggested by the manufacturer. 5 minutes, still drips.
3. So, we tested the circuits. 120 volts feeding the motor. We had a timer switch on it, so I changed it to a regular light switch. 5 minutes, still drips.
4. I took the flapper off the roof vent. 5 minutes, still leaks.
5. There is really no room to reroute the ducting as the roof vent sits just down from the pony support wall top plate and stud (It's literally backed into a corner).
I am at a loss...do you think one elbow at the beginning would slow it down enough to back it up like that and make all the moisture condense in the housing or am I, and everyone I have talked to so far, missing something?