Bathroom Exhaust Fan Basics

What’s your biggest complaint with the bathroom after you take a shower? Foggy mirror? Slippery floors? Sure, both are annoying, but the moist air poses a threat to your long-term health by creating an environment in which mold, mildew, and bacteria thrive.

In a world where mold-inducing moisture threatens our bathrooms, what are we to do? The answer is clear: we must ensure that our homes are properly ventilated. And an essential part of any whole-house ventilation strategy includes bathroom exhaust fans.

About Bathroom Exhaust Fans

How do bathroom fans work, and what do they do?

How. Bathroom fans consist of an electric motor, a fan, ductwork, a vent or hood, and a bathroom vent cover. The electric motor pulls the moist air into ductwork that leaves the house through a vent (soffit or side of the house) or hood (roof).

What. Bathroom exhaust fans are part of your home’s ventilation system. Like attic and kitchen fans, they draw hot, humid air out of your home. Bathroom fans pull moist air out of your bathroom before it has a chance to condense on the floors (causing a slipping hazard) or on the walls (where it encourages bacteria, mold, and mildew growth).

These fans can also be useful in removing harmful odors and fumes from cleaning materials. Bathrooms are subjected to some of the harshest housecleaning chemicals available (try one of these alternatives), putting homeowners at risk of inhalation if the space isn’t properly ventilated.

Do you really need that bathroom fan?

The short answer: Yes, it’s probably the safe thing to do. If you have one, it doesn’t make sense to risk mold growth by not using it. If you don’t have one, you should think about your bathroom’s ventilation. As most state building codes require them, bathroom exhaust fans are generally standard in new constructions, though some states have exceptions for bathrooms with windows.

Because you regularly run water in the bathroom (shower, sink, toilet, etc.), bathrooms are at a greater risk for mold growth than other places in your home. The frequent running water creates a humid environment that provides the perfect home for mold and mildew.

If you notice any of these issues, it might be time to consider having a bathroom fan installed:

• Mold or mildew growth
• Musty smell
• Peeling paint
• Damage to tile, grout, flooring, cabinet finish, hardware, and/or fixtures
• Condensation-covered, slippery tile
• Wet walls that don’t dry out

How long should you run the exhaust fan?

Suggestions for ‘proper’ fan use range from 15 minutes to half an hour. Use your judgment, and keep the fan on for as long as you feel is necessary. Not all bathrooms are the same size, and some people take longer, hotter showers than others, so the time it takes to remove humidity will vary according to the space and water usage.

Types of fans

Exhaust fans for bathrooms are available in a variety of mounting styles with different venting options (roof, soffit, sidewall). If you’re worried about aesthetics, more modern, hidden options are also available.

• Ceiling-mounted. This is the most common type of bathroom fan. It pulls air up through the bathroom fan vent.
• Wall-mounted. These units are installed on the wall. Wall-mounted bathroom fans installed on exterior walls don’t require ductwork.
• Inline. This type of fan has the lowest profile, only requiring a small vent in the bathroom. The actual fan is installed in the attic where it blows humid air out of the home through ductwork.
• Combination units. Bathroom fans have come a long way, and many homeowners are attracted to combination units that offer lighting, heating, and humidity sensing.

Bathroom Exhaust Fan Maintenance: Cleaning and Troubleshooting Common Issues

How to clean your bathroom fan

Follow these steps to clean your exhaust fan:

• Make sure the fan is turned off (either through the switch or circuit breaker).
• Take off bathroom vent fan cover.
• To clean the bathroom vent cover, use soap and water to remove dust and debris.
• Depending on your unit, you might be able to remove the fan/motor for a more thorough cleaning. If that’s not possible, use a vacuum with a tool attachment to vacuum the fan.
• Once everything is clean, return the motor and/or vent cover to the housing unit.
• Turn on the power.
• Test the fan.

How to test your bathroom exhaust fan:

The easiest way to test your bathroom fan is through the toilet paper test.

• Take a square of toilet paper.
• Turn on the fan.
• Put the toilet paper up to the fan.
• If the fan draws in the toilet paper to the cover, it’s working properly.
• Turn off the fan, and remove the toilet paper.

Troubleshooting common bathroom exhaust fan issues

Incorrect size. Not all fans are created equal. Bathroom fans come in a variety of powers based on CFM (cubic feet per minute). For a fan to be efficient, it should move a cubic foot of air per minute for each square foot.

For bathrooms smaller than 100 square feet, measure the room’s length and width to find out the minimum cubic feed needed. For larger bathrooms, count every tub, toilet, shower, and tub as an additional 50 cubic square feet (100 for whirlpool bath). 

Restricted airflow. Does your bathroom have anywhere to draw in fresh air? Having a fan is great, but if the room is too airtight, your fan will struggle trying to replace the humid air. Is there space under the door? You might need to leave the door cracked if this is an issue.

Too noisy. Some people complain that their fans are too noisy. Unfortunately, there’s no way to fix this issue without replacing the unit. The good news is you can be sure to take sones (measurement of noise) into account in your search for a replacement. The lower the sones, the quieter the fan.

Ductwork. Depending on where your exhaust fan ductwork is, issues with the fan might be more difficult to address. The length and number of elbows in ductwork can affect an exhaust fan’s efficiency.

The shorter the ductwork, the more efficient it is, so try to keep the length under ten feet. If the number of elbows is greater than three, the humid air might be struggling to exit your home. It’s important to keep the ductwork as streamlined as possible.

Venting into the attic. Venting exhaust fans into attic space was common before building codes were updated to address issues caused by the humid air. Bathroom exhaust fans exist to remove moist air from your home, and the last thing you want is for that moist air to be hanging out in your attic where it can cause attic mold issues.

Bottom Line:

• Proper bathroom ventilation (through bathroom exhaust fans) is an essential weapon in the war on mold and mildew.
• Bathroom fans use a motor and ductwork to draw humid air out of your home.
• If you have a fan, use it. If you don’t have a fan, find out if your bathroom has enough ventilation to justify not installing one.
• An exhaust fan needs to be installed correctly for it to work most effectively. Many common issues are due to poor installation and shortcuts.

If you’re having issues with mold or mildew in your bathroom, consider installing a bathroom fan, or, if your bathroom is already equipped with a fan, have a professional take a look at it to make sure it’s working properly.