You flip the switch and nothing happens. Or the fan hums without spinning, rattles, or runs but the mirror still fogs over and the paint above the shower keeps peeling. A bathroom fan is easy to ignore until moisture starts showing up as mildew on the ceiling.
This guide helps you pin down what is wrong by symptom: a fan that is completely dead, one that hums but does not turn, and one that runs but does not move air. It also covers duct problems, how to size a new fan using industry guidance, and how to replace one safely.
Quick answer: If the fan is silent, check the breaker, any GFCI outlet on the circuit, the wall switch, and the motor plug inside the fan housing. If it hums but does not spin, turn off the power, clean the dust off the blower and check that the wheel turns freely; a stiff or seized motor usually needs replacing. If it runs but does not clear steam, the duct is likely crushed, disconnected or blocked at the outside vent, or the fan is too small for the room.
Match the symptom to the cause
| Symptom | Likely cause | First fix to try |
|---|---|---|
| No sound at all, light also off | Tripped breaker or GFCI, failed switch | Reset breaker or GFCI, test the switch |
| Light works, fan silent | Motor unplugged inside housing, failed motor, bad fan switch | Check the motor plug, then test the motor |
| Hums but does not spin | Dust-packed or seized motor, failing capacitor | Clean and spin by hand, replace motor if stiff |
| Spins slowly or rattles | Dust buildup, worn bearings, loose housing | Clean, tighten mounting screws |
| Runs, but mirror stays fogged | Crushed or blocked duct, stuck damper, undersized fan | Tissue test, inspect duct and outside vent |
| Water drips from the fan | Condensation in an uninsulated duct, roof leak | Insulate duct, check roof cap |
| Turns on by itself | Humidity or motion sensor | Adjust or replace the sensor control |
Safety first, plus the tools you need
Safety note: Turn off the circuit breaker before removing the grille or touching the motor, not just the wall switch. Confirm the power is off with a non-contact voltage tester. Work from a sturdy step ladder positioned on a dry floor, and if your bathroom fan is over a tub or shower, any replacement must be rated for that location.
Tools and materials
- Sturdy step ladder
- Non-contact voltage tester and a multimeter
- Screwdrivers and a nut driver
- Vacuum with a brush attachment, soft brush and microfiber cloth
- Mild dish soap and warm water for the grille
- Foil HVAC tape and a duct clamp (for duct repairs)
- Replacement motor or fan, if needed
If the fan is completely dead
1. Check the breaker and GFCI
Many bathroom fans share a circuit with the bathroom outlets, which are GFCI protected. Look for a tripped GFCI in the bathroom, a nearby bathroom, the garage or the basement, and press Reset. Then check the breaker panel. If the GFCI trips repeatedly, see our guide to a GFCI outlet that keeps tripping.
2. Check the switch, timer or humidity control
Wall switches wear out, especially timers and humidity-sensing controls that see heavy use. If the fan shares a switch with the light and the light works, the switch is probably fine. If the fan has its own switch, it may have failed. With the power off, you can test it for continuity with a multimeter, or simply swap in a new one. Our guide on how to replace a light switch covers the wiring basics.
3. Check the motor plug
Most fans have a small plug that connects the motor to a receptacle inside the housing. With the breaker off, remove the grille by pulling it down and squeezing the spring clips. Check that the motor plug is pushed fully into its receptacle. Vibration can loosen it over time.
4. Confirm whether power reaches the fan
If the plug is seated and the switch is good, the motor has likely failed. If you are comfortable using a multimeter, you can test the motor windings for continuity with the power off. If you are not sure whether power is reaching the housing, stop here and call an electrician rather than testing a live circuit overhead.
If the fan hums but will not spin
A humming fan is getting power, but the motor cannot turn the blower. Dust and lint mixed with bathroom moisture form a sticky paste that slows the wheel, and after years of service the bearings wear and the motor seizes.
Clean the fan
- Turn off the breaker and confirm the power is off.
- Pull the grille down, squeeze the spring clips and remove it. Wash it in warm soapy water and let it dry.
- Vacuum the housing, the motor and the blower wheel with a brush attachment.
- Wipe the blades or wheel fins with a damp microfiber cloth, keeping water away from the motor.
- Spin the wheel by hand. It should turn smoothly and coast for a moment.
Free or replace a seized motor
If the wheel feels stiff, gritty or will not turn at all, the motor bearings are worn. Some older motors have oil ports, and a drop or two of lightweight electric motor oil can buy time. Many modern motors use sealed bearings that should not be oiled, so check the manual first. Avoid penetrating sprays, which attract more dust.
Replacement motors are sold for many popular models. Unplug the motor, remove the mounting screw or bracket, and lift out the motor and wheel together. Copy the model and part numbers from the fan’s label before you order, since a mismatched motor can be noisy or move less air. If the fan is more than 10 to 15 years old, replacing the whole unit often costs little more and gives you a quieter, more efficient fan.
If the fan runs but does not clear the steam
Do the tissue test
Turn the fan on and hold a single square of toilet paper against the grille. A healthy fan holds it in place. If the paper falls or barely moves, airflow is restricted somewhere between the fan and the outdoors.
Inspect the duct
Duct problems are the most common reason a running fan does not work well. Go to the attic, if you can reach the fan from above, and look for these issues:
- Disconnected or missing duct. Fans are sometimes left blowing into the attic, which feeds attic moisture and mold.
- Crushed or kinked flex duct. Insulation, storage or foot traffic can flatten it.
- Long, saggy runs. Low spots collect condensation and restrict flow.
- A stuck damper. The flap at the fan or the outside cap may be stuck shut with lint, paint or a nest.
The Building America Solution Center recommends venting fans outdoors only, never into an attic, crawlspace or wall cavity. It also advises using smooth rigid duct where possible, keeping runs short with few bends, keeping the first three feet from the fan straight, sealing joints with mastic or metal tape, and insulating the duct to reduce condensation.
Give the fan air to replace
A fan cannot pull air out of a sealed room. If your bathroom door seals tightly against the floor, air has nowhere to come from. A modest gap under the door or a transfer grille lets replacement air in so the fan can work as designed.
Check the fan size
An older or builder-grade fan may simply be too small. The next section shows how to size one correctly.
How to size a bathroom fan
The Home Ventilating Institute’s bathroom ventilation guidance recommends 1 CFM (cubic feet per minute) per square foot for bathrooms up to 100 square feet, which works out to about eight air changes per hour. For larger bathrooms, HVI suggests sizing by fixture instead: 50 CFM each for a toilet, shower and bathtub, and 100 CFM for a jetted tub.
| Bathroom | Floor area | Suggested minimum |
|---|---|---|
| Powder room, 5 x 6 ft | 30 sq ft | 50 CFM (code minimum in many areas) |
| Hall bath, 5 x 8 ft | 40 sq ft | 50 CFM |
| Primary bath, 8 x 10 ft | 80 sq ft | 80 CFM |
| Large bath with toilet, shower and tub | Over 100 sq ft | 150 CFM |
| Large bath with toilet, shower and jetted tub | Over 100 sq ft | 200 CFM |
Many codes require at least 50 CFM for a fan used intermittently, so round small rooms up to that. Because ducts reduce real-world airflow, a fan rated a little above your minimum helps. Look at the sone rating too: a lower number means a quieter fan, and a quiet fan is one people actually use. HVI also recommends running the fan for about 20 minutes after a shower, which a timer switch makes easy.
How to replace a bathroom fan safely
If you are replacing a fan in the same spot with the same duct size, this is a manageable DIY project. Many manufacturers sell retrofit or upgrade fans designed to fit existing housings or to install from below without attic access.
- Turn off the breaker and verify the power is off at the fan with a voltage tester.
- Remove the grille, unplug the motor and remove the motor assembly.
- Open the wiring cover, note which wires connect where, then remove the wire nuts and disconnect the cable.
- Detach the duct from the housing and remove the housing from the joist, working from the attic or from below depending on the model.
- Install the new housing, matching the duct size. Do not step down from 4-inch duct to a 3-inch fan connector unless the instructions allow it.
- Connect the duct with a clamp and seal it with foil tape. Confirm the damper flap moves freely.
- Connect black to black, white to white and ground to ground with new wire nuts, then close the wiring cover.
- Install the motor and grille, restore power and run the tissue test.
If you need new wiring, a new duct run or a roof or wall vent, the job usually calls for an electrician or ventilation contractor.
Common mistakes to avoid
- Only turning off the wall switch. Always use the breaker and confirm with a tester.
- Venting into the attic or a soffit vent. Moist air ends up in the attic, where it can cause mold and wet insulation.
- Buying by CFM alone. A long, kinked duct can cut a fan’s real airflow dramatically.
- Turning the fan off when you leave. Running it about 20 minutes after a shower is what prevents bathroom mold.
When to call a pro
- You smell burning, see scorch marks or the fan trips a breaker.
- There is no power at the fan and the switch and breaker check out.
- You need new wiring, a new circuit or a fan over a tub or shower.
- Water drips from the fan or ceiling, or the duct runs to the attic with no exterior vent.
According to HomeAdvisor’s bathroom fan cost guide, installing a bathroom fan typically costs $240 to $564. Swapping an existing fan where the wiring and duct are reused typically adds $100 to $400 in labor to the cost of the fan.
| Job | Typical cost range |
|---|---|
| Bathroom fan installation overall | $240 to $564 |
| Labor to replace an existing fan | $100 to $400 |
| Electrician hourly rate | $50 to $130 per hour |
| Wall vent installation | $250 to $800 |
| Roof vent installation | $350 to $950 |
Frequently asked questions
Why is my bathroom fan humming but not spinning?
The motor is getting power but cannot turn, usually because of packed dust or worn bearings. Turn off the breaker, clean the blower and spin it by hand. If it feels stiff, replace the motor or the whole fan.
Can I replace just the motor in a bathroom fan?
Yes, for many models. Match the model and part number from the label inside the housing. For older or discontinued fans, a retrofit fan that fits the existing opening is often the easier path.
How long should a bathroom fan run after a shower?
HVI recommends about 20 minutes after bathroom use. A countdown timer or humidity-sensing switch handles this automatically, so nobody has to remember.
Is it OK for a bathroom fan to vent into the attic?
No. The moist air can condense on roof sheathing and insulation, leading to mold and rot. The duct should end at a dedicated roof or wall cap with a damper.
Why does water drip from my bathroom fan?
Usually warm, moist air condenses in a cold, uninsulated duct and runs back into the fan. Insulate the duct, slope it toward the exterior where possible, and run the fan longer. A damaged roof cap can also let rain in.
The bottom line
Start with the symptom. A silent fan points to power, the switch or the motor plug; a humming fan needs cleaning or a new motor; and a fan that runs without clearing steam almost always has a duct, damper or sizing problem. Always shut off the breaker first, size replacements by HVI guidance, and make sure the duct ends outdoors.
