Bathroom Exhaust Fan Buying Guide

Make sure the fan you choose is powerful enough to ventilate your bathroom. The room’s size determines the necessary cubic feet per minute (CFM) rating of the fan. The CFM rating measures the volume of air the fan moves. As a general rule, you’ll need at least 1 CFM per square foot of space. A fan that’s too small won’t remove moisture and odors efficiently and will need to run longer, increasing wear on the motor. The following guidelines can help you find the right fan for rooms with 8-foot ceilings.

• A bathroom 50 square feet or smaller needs a 50-CFM fan.
• For bathrooms between 50 and 100 square feet, estimate approximately 1 CFM per square foot.
• If your bathroom is larger than 100 square feet, tally the CFM requirements for the individual fixtures to estimate your needs. Plan for 50 CFM for each toilet, tub and shower and add 100 CFM for a jetted tub.
• If your bathroom is smaller than 50 square feet, a 50-CFM fan will work.
• Regardless of the room size, a long run of duct work connecting the fan to the outside increases the CFM requirements, particularly if there are bends in the run.

Note that if your bathroom has an enclosed toilet area, the space needs its own fan.

While the fan’s CFM should be rated for the square footage of the room, it’s a good idea to size the fan up a little. For example, get a 70-CFM fan for a room that’s 65 square feet.

How Do Bathroom Exhaust Fans Work?

Moisture from hot showers, baths and other fixtures can accumulate on your bathroom walls, windows and cabinets. Without proper ventilation, this moisture can lead to mold and mildew growth, peeling paint, damaged wallpaper and warped walls and cabinetry. 

An appropriately sized and installed bathroom exhaust fan will remove the moist air and prevent these problems. Plus, bathroom fans can help improve overall air quality and remove odors.  

The best bathroom exhaust fans connect to your home’s existing vent ducts and channel the moist air outside. Some types of bathroom fans only vent moist air to the space in between your ceiling joists or into an attic. While easier and quicker to install, these bathroom fans can contribute to moisture damage elsewhere in your home in the long run. If your local building codes require an exhaust fan in bathrooms, then they also likely require that the fan vents air directly outside, rather than into other parts of your home. 

We recommend always venting your fans to the outside and never into an attic or crawlspace.