Home House & Components Appliances Exhaust Fans
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. Ventilation Exhaust Fans
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.
Below are some of the most frequently encountered issues with residential bath fans.
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.
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.
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.
An airtight bathroom may not provide adequate replacement air for the fan to function properly.
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.
Condensation buildup in the ductwork can lead to dripping water from the fan grill or ceiling stains. Here are some reasons why.
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.
In colder climates, ducts need to be fully encased in insulation. Without it, the duct never warms up and condensation builds up.
“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.
Over the years, fans become noisy as the motor parts wear out.
If the damper is stuck open, this allows cold air in. Remove any debris or obstructions that are keeping it open.
Take into account the bathroom’s dimensions, the fan’s noise level rating and its overall quality.
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” 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.
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.
Yes. Alternatively, a window can be used to vent a bathroom.
Yes. “Fans circulate the air and can help dissipate odors,” Danielson says.
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.
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