As a home inspector, I have inspected hundreds of bathroom fans and this is a quick and dirty guide to checking a bathroom fan that is not pulling air.
In this guide, I will go over…
- The toilet paper test for suction
- Checking the bath fan grille
- Inspecting the duct and exterior hood
- Checking for dust buildup on the motor
Toilet Paper Test
The easiest and most common way to check a bathroom exhaust fan is the toilet paper test. Simply turn the bathroom fan on, and then take a single square of toilet paper, and put it up to the bathroom fan grille.
You can also place a square of paper towel (rather than toilet paper) since it’s a bit heavier and will indicate more suction.
If the bathroom fan is working and sucking in air, then the single piece of toilet paper should stick to the grille without you touching it. Of course, this doesn’t necessarily mean that the bathroom fan is running at 100% capacity, but it is a good basic test to see if there is suction.
Bathroom Fan Cover (Grille)
If the toilet paper test failed, and the bathroom exhaust fan is not pulling air — it is a good idea to check the grille for dust.
It is pretty common for bathroom vent fan covers to get clogged with dust and debris — blocking air flow. Fortunately, bath fan grilles are very easy to clean.
Most covers are held in place with spring clips which are easy to undo. All that is required is to pull down on the cover for about an inch, and then reach behind the cover with your fingers and squeeze the spring clip on each side.
Squeezing the clips together will release the cover.
And then you can simply take the bathroom grille to the sink and clean it.
Checking The Motor
In addition to the bathroom fan cover, another important place to check is the housing and motor for dust buildup.
If the motor is caked with dust, it will cause the motor to overheat, lowering its efficiency, lowering its lifespan, and it may even result in a fire.
Believe it or not, numerous home fires are started every year because of bathroom vent fans overheating. Fortunately, newer fans have thermal safety switches that will turn off the fan if it overheats, but if you have an older bath fan you may be out of luck.
If you have an older fan that doesn’t have a permanently sealed motor, it is smart to oil the motor and shaft every few years — it can make a big difference in performance. To learn more, you can read my guide on how to oil bathroom fans.
Cleaning The Motor And Housing
Before even attempting to clean a bathroom fan motor (and housing) — you should cut off the power to the unit at the electrical panel. You don’t want to get shocked.
If the motor and housing is very dusty, you may want to try cleaning it with a can of compressed air — the things used to clean computer keyboards.
You can also just use some wet wipes to clean it by hand.
If that doesn’t work, you can try using a vacuum cleaner with a brush attachment. And as a last resort, you may need to remove the housing to properly clean it.
Exterior Vent Hood
The exterior vent hood is also an important part of the bathroom fan to inspect. This is the cover on the outside that has a flapper and possibly a screen.
If the exterior hood has a blockage or isn’t working properly, then it will severely restrict the air flow of the bath fan.
The best way to check the exterior vent hood is to first turn on the bathroom exhaust fan. With the exhaust fan turned on, check the exterior hood for strong air flow. If the air flow is very weak, then there may be an interior duct blockage preventing air flow.
Check The Flapper
Sometimes the damper flap also gets stuck due to insects, bird nests, and debris.
The flapper is supposed to open when the bath fan is on, but it should automatically close when it is turned off.
If there is no flapper, then that is also a problem because it may allow in pests and exterior unconditioned air.
If the exterior hood has a pest screen, then make sure that the screen isn’t clogged with debris impeding air flow as well. I recommend opening up the flapper, and shining a flashlight into the duct to look for obstructions.
Check The Bathroom Fan Duct
If your bathroom fan duct goes through an unconditioned area such as an attic or crawlspace, it’s a good idea to inspect the duct to make sure it’s in good condition.
Ideally the duct should go in a straight line to the outside, whether it is the roof or exterior wall.
Having as few bends and dips possible will maximize the air flow of the exhaust fan.
And if the duct is going through an unconditioned area like an attic, you want to closely inspect it for signs of water problems (condensation). If you have any signs of water or condensation along the duct, you may need to insulate the bathroom fan duct. If you want more details, you can read my guide on how to insulate bathroom fan ducts.