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Bathroom exhaust fan problems

About a year ago I installed a bathroom ceiling fan,  Recently I have paint starting to bubble on the ceiling next to the fan.  It appears that the moisture is collecting in the vent pipe and running back down to the fan and not escaping the house.  This is the second time I have had this problem.  The fan is double the CFM required for  the size of the bathroom and the exhaust pipe is clear. 


Any help resolving this would be appreciated.

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Posted 2011-01-30T16:58:57+0000  by home_diy_guy home_diy_guy

Hey DIY GUY.  Welcome back to the community.


   Is the "bubbled" paint new or has it been happening for a while now? Also, look for discoloration around the area of the vent (dark yellow water stains). It is possible that either the vent pipe has separated from the exhaust fan or that there might be a leak in the roof around where the pipe exits. One more possible cause would be if the shower is located right under the exhaust  fan then it could become "overloaded" with moisture. These fans are mainly used to vent air through the room which aids in circulation and reducing humidity.


water stains.jpg




   It may be something as simple as cracking a window or door open a little bit while the shower is in operation until the initial steam subsides.   


I hope this helped you out a little. Check it all out and get back to me so we can tackle it together.

Posted 2011-01-30T18:16:54+0000  by Kevin_HD_ATL

Thanks for the response.

My home was built in the 50's and has plaster walls, except where I have renovated.

The bubbling of the paint appears to be a build up over a relatively short period of time. 

There is not any discoloration of the paint, the plaster just slowly absorbs the moisture until it pushes the paint free.

Then it will dry and the bubble blends back in with the ceiling surface.

I have checked both the attach point and the exit and they are tight, not water tight, but there are no obvious gaps.

The exhaust pipe has 2 turns in it to get to the exit point and it looks like the water condenses on the inside of the pipe and runs back down to the fan.  Then slowly leaks out through the joint where the pipe meets the fan.

I have tried to wait to run the fan until the bathroom door is open, but it does not seam to help.

I even run the fan for a half our or more after a shower to help provide more air movement to dry the pipe.


I am not sure how to correct this problem, but in a small bathroom like mine moisture is a problem if I don't have an exhaust fan.

Posted 2011-01-30T19:51:34+0000  by home_diy_guy

   The moisture is getting in from somewhere... The fan should act as a direct flow from fan to pipe to outside. I recommend sealing anywhere you see space around the inside of the fan housing. If the gaps are very large, then try using expanding foam. If the gaps are small - use silicone to seal all edges. Lastly, prime any exposed plaster still visible inside the fan housing and seal the "bubbled up" areas as well. This should do it.


Keep me posted :smileyvery-happy:

Posted 2011-01-30T20:01:24+0000  by Kevin_HD_ATL

Thanks,  I'll look into sealing the joints.

Posted 2011-01-30T20:25:43+0000  by home_diy_guy

Is the vent pipe running through an unheated attic space? The warm moist bathroom air may be cooling too quickly in the pipe and the condenstion is what is running back to the fan. You could try to insulate the exhaust.

Posted 2011-02-11T17:25:15+0000  by ebourke
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