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Discussion Starter · #1 ·
Hello,

the ceiling area around my bathroom exhaust fan has been getting soaked because of the condensation of the hot showers and the cold winter air from the attic. I did fix this issue somewhat by going into my attic and replacing the old cracking duct with an insulated one. However, I am still getting water dripping down from the exhaust fan.

I pulled down the exhaust can cover and did notice gaps around the exhaust fan box. Perhaps this is the culprit.
Just wondering, what is the best way to seal up those gaps? Expanding foam sealant, such as "Great Stuff"? Or silver sealing tape for HVAC purposes? Or both?
I have attached some pictures here:
https://goo.gl/photos/zWX9LDVFYJEUHkNE8
 

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Did you clear any blockages from the exit point, often things accumulate there and block some of the air flow.

Is the exhaust fan being ran long enough after showering to rid the system of any moist air?

Run the fan an extra 10 minutes after finishing, this will send all the moisture away.

As for sealing the gaps, either of your ideas will work, Myself I would use a minimal expanding foam.


ED
 

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Discussion Starter · #3 ·
Hi Ed,

thanks for your reply. No blockage at the exit point as it's a new vent the roofers installed when I got my shingles replaced a month ago. I even checked by going up on my roof to see if there are indeed any blockages. I also checked to see if the seal around the vent and duct were intact and they looked fine.

Yes, I am running the exhaust fan for more than 10 minutes after every shower.

Is Great Stuff the best stuff to use or is there another expanding foam that would be better for this application?
 

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Bath fans often have an internal damper which open under air pressure to exhaust the air. Unfortunately, it may also be opening slightly due to normal house pressures allowing a trickle of warm air into that exhaust duct. A trickle is worse than running the fan because that air cools before it exits thus leaving the moisture behind.

They make inline dampers that work well in a vertical position. If your duct run is horizontal then keeping it flat and sloped to the outside may help.

As for sealing, you can build a simple box with drywall and caulking around it and then bury that in insulation. Sometimes easier to seal it by encapsulating the entire fan assembly than sealing the assembly to the drywall. If code will allow, build the box out of rigid foam.

Bud
 

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From the attic I would cut some pieces of ridged foam or sheet rock and lay it on the sheet rock and extend it over the gap and butt it against the fan housing.....seal the joint with flexible caulk. You can use expanding foam but it goes all over the place and it may be tricky to fill the gaps. If you want the sheet rock fix to look really neat after spanning the gaps around the fan housing attach pieces of sheet rock from the bathroom side. Also, is the ductwork from the fan to the roof vent insulated? Check the exhaust fan instructions or contact the manufacturer to check insulating instructions.
 

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Seal the gaps and unused holes with aluminum HVAC tape (NOT 'duct tape'). Use expanding foam to seal the crack between the fan housing and the top of the bathroom ceiling. Build up insulation around the fan housing. Use more of whatever kind of insulation is in your attic now.

From the inside, with the grill off the fan housing, use more aluminum tape to seal the inside of the housing to the ceiling, keeping inside the footprint of the grill.
 

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Think you are trying to solve the wrong problem. Sounds like the fan is not pulling air out of bath.
Turn fan on and hold tissue or paper towel up to grill. If fan is actually pulling air out it will hold tissue up against grill.

Having door open helps exhaust humidity from the room.
 
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