More in Ventilation

Failing Exhaust Fan

Q: What's wrong with my bath fan?

Save the Bay Tom Silva

The fan in my bathroom doesn't seem to operate properly. The motor works (though it's loud), but after a shower, the walls, cabinets, and mirrors are wet. Even the medicine cabinet is rusting. Also, the fan seems to blow out a lot of dust. What's wrong?
— Susan, Eugene, OR


Tom Silva replies: Well, it could be several things. Perhaps the exhaust duct is clogged or disconnected, or the flapper in the exhaust vent hood is jammed (see Homeowner's Handbook). Or maybe the fan is too small for the size of the room, or it might be that there isn't enough air coming into the room to make up for all that the fan is trying to suck out of the room.
But the fact that the unit is blowing dust makes me wonder if it's even hooked up to an exhaust duct at all. Maybe you have one of those recirculating fans, which have no ducts to get rid of moisture; they only filter out odors. To find out, remove the fan grille. A recirculating fan contains filters; an exhaust fan doesn't. Cleaning or replacing the filters will stop the dust.
Now, if you see an obvious connection to a tubular duct when the grille is off, and the vent hood flap is clear, you'll have to find and loosen a blockage in the duct. Don't use anything sharp like a coat hanger; it will poke holes in the duct. Instead, get one of those brushes designed for cleaning dryer ducts, and work from the inside out. When the clog is gone, there should be enough airflow when the fan is on to hold a tissue tightly in place over the grille. And just to make sure the duct is attached at both ends, hold a plastic bag tightly over the outside vent hood while the fan is on; it should inflate in a matter of seconds.


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