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Small Drip, Awkward Location

What to do when a ceiling vent dribbles into the bathroom

Ask This Old House Crew
Photo by Matt Kalinowski

During the winter, tiny drops of water fall from the fan in our bathroom ceiling. The good thing is that they drip into the toilet. The bad thing is that anyone using the toilet gets wet. The drip isn't constant, but seems to occur after we've showered, when the fan has been on for a while.
— Lowell, Rawson, OH


Tom Silva replies: If your exhaust duct runs through a cold attic, moisture is probably condensing on its inner surface and dripping out the fan grate. This is more than a nuisance, because water running back into the fan unit can lead to problems there. Luckily, the fix is easy.
First, make sure that the exhaust cap isn't clogged or blocked. Then insulate the exhaust piping with fiberglass batts or duct insulation. Another thing that might help is to run the fan for several minutes before you turn on the shower; that will increase the temperature of the duct just enough to minimize condensation.
Even if the duct isn't running through a cold space, however, it should be sloped slightly toward the outside of the house so that moisture doesn't roll back toward the fan. Also, try to run the fan for at least 15 minutes after your shower to encourage any moisture to leave the room. That's the reason all the bathroom fans in my house are on timers.


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