Recognizing and Correcting Common Bath Fan Problems

Updated: May 19, 2024

A bath fan that isn't installed properly can cause more damage than no fan at all. But here's the good news: Bath fans aren't that complicated.

Bath fans do more than prevent a foggy bathroom mirror after a hot shower, they remove excess bathroom humidity. “If a bathroom is not properly vented many possible issues could arise,” says indoor air quality expert Dave Jones. These issues include mold, rot or paint damage.

In my first home, the bathroom fan vented into the attic instead of outside, causing major mold damage. With the help of three industry experts, Jones from Broan-NuTone, Stan Pollack from Stan-the-Fixit-Man and Caroline Danielson from Ferguson Enterprises, learn to recognize and correct almost any bathroom fan problem yourself.

Common Bath Fan Problems and Solutions

Below are some of the most frequently encountered issues with residential bath fans.

The fan is running but not working

To test if your fan effectively expels air and moisture, hold an extinguished match near it to see if the smoke drifts towards it, or place a tissue over the fan grille to check if the suction holds it in place. If it fails either of these tests, here are some likely causes and solutions.

The grille is dirty

Bath fans draw in dust and lint, which can eventually clog the grille and limit airflow. “Fans should be cleaned periodically, ideally every year or two,” Pollack says.

  • Solution: Jones recommends removing the cover or grille and then cleaning it with warm, soapy water. While the grill is off, carefully vacuum the fan.

The dampers are stuck

There are two dampers for a bath fan, one at the housing and another where the duct exits the building. If they don’t open easily or fully, airflow will be weak. According to Pollack, this happens most frequently on outside dampers.

  • Solution: Move the exterior damper by hand to ensure it opens easily. Clean away any debris that might hinder movement. Push open the interior damper with a stiff wire to make sure it’s functioning.

The bathroom is too airtight

An airtight bathroom may not provide adequate replacement air for the fan to function properly.

  • Solutions: Leave the door cracked open while the fan is running or trim the bottom of the door to leave a 1/2-in. gap between the door and the floor.

Ductwork issues

If your fan is running but not working “there’s a potential that the duct is unattached,” Danielson says, or has a hole or tear. Also, ductwork that has too many turns or is too long can inhibit air pull. In this case, “the fan is not strong enough to push the moist air through the entire length,” Pollack says. Every fan will have different allowable duct lengths, so consult your owner’s manual.

  • Solutions: Visually inspect that the duct is attached to the fan and the vent hood. Also repair any holes or tears with aluminum tape. Consider rerouting ductwork that is very long or has several sharp corners.

Drips and water stains

Condensation buildup in the ductwork can lead to dripping water from the fan grill or ceiling stains. Here are some reasons why.

The outside damper is stuck

If the damper doesn’t open, the fan may drive enough air through the duct to cause condensation, but not enough to warm the duct and dry it out.

  • Solution: Make sure the outside damper isn’t obstructed or stuck.

Missing insulation

In colder climates, ducts need to be fully encased in insulation. Without it, the duct never warms up and condensation builds up.

  • Solutions: Add insulation or reattach loose insulation with aluminum tape.

Fan is vented into the attic

“Bath fans should be vented outside,” Jones says. If they’re not, warm air can condense on framing and sheathing in the attic, causing mold, rot or ceiling stains. Warm attic air can also lead to ice dams.

  • Solution: Make sure ductwork terminates outside through the siding or an attic window.

Other potential problems

Noisy fan

Over the years, fans become noisy as the motor parts wear out.

  • Solution: Replace the fan with a newer model. Pollack also suggests just replacing the motor if the fan model allows it.

Cold air is coming in

If the damper is stuck open, this allows cold air in. Remove any debris or obstructions that are keeping it open.

What to Consider When Shopping For a New Bath Fan

Take into account the bathroom’s dimensions, the fan’s noise level rating and its overall quality.

Room size

Fan capacity is rated in cubic feet per minute, or CFM. You should choose a fan with a CFM rating that is slightly more than the square footage of your bathroom. “The larger the room the higher the CFM you’ll need,” Danielson says.

Sone rating

“Sone” is the term used in the industry to describe how loud a bath fan is. The lower the number, the quieter the fan will be. “Typical bath fans range anywhere from 0.3 sones to 6.0 sones,” Jones says.

  • Pro Tip: Experts generally recommend fans with ratings of 1.5 or less.

Quality

Most home centers have basic bath fans for about $30, but they’re loud and have low CFM ratings. It’s smart to spend at least twice that; you’ll get a fan that’s quieter, pushes more air and is likely to last longer.

FAQs

Is it OK to not have a fan in the bathroom?

Yes. Alternatively, a window can be used to vent a bathroom.

Do bathroom fans get rid of smells?

Yes. “Fans circulate the air and can help dissipate odors,” Danielson says.

About the Experts

Stan Pollack is the owner of Stan-the-Fixit-Man, offering a wide variety of handyman services since 1982. He has also been an instructor of Home Repair classes for adults in his community for 25 years.

Caroline Danielson is Director of Showrooms for Ferguson Enterprises, a top retailer of high-end kitchen, bathroom and lighting fixtures. She has been with Ferguson for eighteen years.

Dave Jones is an Indoor Air Quality Expert at Broan-NuTone, a leading global brand of residential ventilation products. He is also host of the Healthier Homes Podcast.