I just moved into my first home, and the bathroom fan is 100% ineffective. I can hear the motor run when I turn it on, and I remember going into the attic with the home inspector and tracing a flexible duct from the fan fixture out to a port on the side of the house. The fan was installed when the previous owners renovated the bathroom three years ago, so it's unlikely it's worn out from age.

But when I turn it on, it has absolutely no effect on the moisture in the bathroom. Water collects on the ceiling and fogs up the mirror and window. The only way to dry the bathroom out after the shower has been used is to open the window or open the hall door - both of which are very slow.

If I hold up a piece of tissue to the fan fixture, it doesn't blow around at all.

What can I do to fix this? Do I simply need a new fan fixture?

  • What is the volume of the bathroom (Length x Width x Height)? Do you know the cubic feet per minute (CFM) rating of the fan? Does the flexible duct sag at all?
    – Tester101
    Commented Jan 6, 2016 at 17:07
  • To make sure the fan is working at all... Rip one square of toilet paper. Turn on the fan. Hold the square of TP against the inlet, and let go of it. If the TP stays in place, at least you know the fan sucks.
    – Tester101
    Commented Jan 6, 2016 at 17:09
  • 1
    Does the port on the side of the house have a flap? If so, does the flap open when the fan is on, or can it be pulled open by hand? Commented Jan 6, 2016 at 17:16
  • 1
    @DanielGriscom Should I try to turn it on then see if I can see the flap move from the ground?
    – Bill
    Commented Jan 6, 2016 at 17:17
  • 1
    Are you able to get back to the attic and the fan? You could disconnect the duct from the fan and try running it then with the toilet paper test. If it sticks, your duct is the problem. If it still doesn't, then it's the fan. I'm sure pulling apart the system isn't the best solution, but hey.. if you're going to possibly replace the fan anyway.
    – TFK
    Commented Jan 6, 2016 at 17:23

3 Answers 3


Various things to check:

  • Is there a way for air to ENTER the bath? A fan will expel air, but only when there is makeup air to replace it. Make sure there is a sufficient gap under the bathroom door. (An easy way to test this issue is to run the fan with and without the door open and see if there is a difference)

  • as others have stated, make sure the fan is clean.

  • as others have stated, check the flexible vent pipe

  • consider replacing the flexible vent pipe. Flexible pipes aren't very efficient in that they add a lot of resistance to the airflow and also snag lots more debris. Consider replacing with rigid vents.

  • as others have stated, make sure the vent on the outside isn't clogged (e.g. bird nest in pipe).

  • consider a larger fan. It could be that the fan is simply under-powered for the size of the room and length of the vent pipe.

  • 1
    I had an electrician put in a 100CFM fan (used to have a 40CFM fan). This did the trick, but I forgot to update the post.
    – Bill
    Commented Feb 5, 2016 at 18:50

Bath fans accumulate lint on the blades. Hair spray and other aerosols exacerbate this. It's inevitable.

I remove the motors from mine every few years and scrape the thick layer of gunk off them, which makes the blades round and not nearly as effective. It's usually a very simple task to pull the cover and the motor plate--as little as one screw holds it in place. Most fan motors have cord plugs that allow easy detachment from the fan housing.

If that's not the issue, remove the plate and determine that the air flap on the fan housing functions as expected and is not obstructed.

  • 1
    Downvoter, care to comment?
    – isherwood
    Commented Jan 7, 2016 at 16:51

The tissue should suck up & stick to the grill. If it doesn't, then remove the grill or cover to see if the plug's cord isn't secured & caught the fan blade &/or spin the fan manually. Then, go down & turn the switch on again to confirm the fan actually spins.

Don't put the grill or cover back on yet, I'm not nearly done.

If the tissue does stick nicely then you'll need to check the actual vent path as thoroughly as you can. Go back to the fan & remove the plug & screw that holds the fan in place. You should see a large hole with a plastic flap & the flap should swing open freely.

Your choice here, you can remove the screws that hold the fan-box up & into the ceiling or you can go up into the attic. Take the box down, remembering or marking its position on the ceiling, & remove the fan-box from the vent hose or duct to visually inspect for a clog of some sort.

If no clog then get a much taller ladder, if you've been standing on the toilet all this time, & get a vacuum with a long hose. Leave the vacuum off & feed the hose as far as it will easily go into the duct. If you meet resistance, then turn on the vacuum & slowly pull out the hose, trying to feel if you caught something at that point & can pull it all of the way out.

If nothing at all & you're like 5-feet into the duct, then you'll have to do this further up in the attic. Compress the duct to get your vacuum hose out to the outside vent head or at least closer to it & suck-up any blockages.

If you still couldn't reach the outside vent head, then get a long pipe to tape to the vacuum & get to that vent head. If all's clear & especially was clear the whole time, then you'll have to check, clear or replace the vent head outside & you might as well get a new fan for the bath after all of this effort.

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