Your bathroom exhaust fan is running but the mirror still fogs up and the humidity never seems to drop. Or maybe the fan isn’t running at all. Either way, something’s wrong — and a non-functioning bathroom fan leads to mold, peeling paint, and wood rot in your ceiling over time.
Here’s how to figure out what’s going on and whether you can fix it yourself.
Case 1: Fan Won’t Turn On At All
Check the Switch and Breaker
Start simple. Is the wall switch working? Try toggling it a few times. Then head to your electrical panel and look for a tripped breaker. Bathroom fans are often on a shared circuit with lights — if the lights still work, the fan may have its own circuit or the fan motor may have failed.
Test for Power at the Fan
With the power off, pull the fan grille down (it usually snaps off or has two small wire clips). Look at the wiring going into the fan housing. If you have a non-contact voltage tester, restore power temporarily and check whether voltage is reaching the unit. If it is, the motor is dead and you need a new fan. If power isn’t reaching it, you have a wiring issue.
Case 2: Fan Runs But Doesn’t Remove Moisture
This is actually the more common complaint — and the fix is usually easy.
Check the Duct Connection
Pop the grille off and look up into the housing. The duct collar should connect securely to a flexible duct or rigid duct that runs to the outside of your home. If the duct has come loose or was never connected properly, the fan is just recirculating bathroom air into your attic — and dumping all that moisture up there, which is a mold nightmare.
Check for a Blocked or Collapsed Duct
Flexible ducts kink and collapse over time, especially in attics where they get walked on or crushed by insulation. Go up into the attic (or hire someone) and trace the duct run from the fan to the exterior vent. Look for kinks, disconnects, or spots where the duct has been squished flat.
Check the Exterior Vent Cap
Outside your home there should be a louvered or dampered vent cap where the duct exits. These caps can get clogged with debris, bird nests, or the damper flap can get stuck closed. Clean it out and make sure the flap opens freely when air blows through.
The Fan Is Just Underpowered
Bathroom fans are rated in CFM (cubic feet per minute). If your fan is old or undersized for your bathroom, it simply won’t move enough air to control moisture — even when working perfectly. The rule of thumb is 1 CFM per square foot of bathroom floor area, with a minimum of 50 CFM.
How to Replace a Bathroom Exhaust Fan
Replacing a bathroom fan yourself is very doable if you’re handy. New fans run $30–$150 depending on features (quiet operation, humidity sensors, built-in lights). The main challenges are attic access for duct work and running power if the location changes.
If you’re uncomfortable with ceiling electrical work, a handyman or electrician can usually swap a fan in 1–2 hours.
Bottom Line
Don’t ignore a dead or struggling bathroom exhaust fan. Moisture is the number one enemy of bathrooms — it causes mold behind walls, rotted joists, and destroyed drywall. A $50 fan and an afternoon of work is a lot cheaper than a bathroom mold remediation job.