Buying Guide

Bathroom Fans Buying Guide

CFM: Measuring Bath Fan Performance According to Bathroom Size

A fan’s ability to move air is measured in cubic feet per minute (CFM). The bigger your bathroom, the higher the CFM rating you’ll need. A fan should have a CFM rating high enough to replace the air in your bathroom at a rate 8 times per hour. 


Determine the size of your bathroom with this formula: Length x Width x Height x 0.13 = Minimum CFM rating


If all else fails, check the packaging. Each bath fan will indicate the maximum square footage it can't ventilate.


Most fans are rated from 50 to 110 CFM. 


  • For bathrooms 50 square feet and smaller, it is recommended you purchase a bath fan designed for small rooms, which will typically have a CFM range of 50-79.               
  • For bathrooms that are larger, select a fan that can move at least 1 CFM per square foot of room. So, for an 80 square foot bathroom, select a fan with at least an 80 CFM rating.
Bath Fan Sone Ratings, Mounting Options and Features

Sone Ratings


The industry standard for measuring the amount of sound a fan makes when it’s in use is called sones. The lower the sone rating, the quieter the fan will be. One sone is equivalent to the sound of a quiet refrigerator, so a quiet bathroom fan will be rated at about 1.5 sones or less. 


Mounting Options


Bathroom fans are available in three models: those that offer ceiling mounts, wall mounts, or both. While the ceiling installation style is the most common, choose the mount type that works best with your bathroom.


Features


  • Consider replacing a light fixture with a bath fan model that features a light. This will allow you to use the existing wiring and switch. 
  • Some models of bathroom fans include built-in heaters to improve warm air circulation or humidity sensors that automatically turn on the fan when it's needed most.
  • If your bathroom fan and bathroom light are installed separately, you will need a  combination switch that has two or three controls. 
  • When installing, remember that fans in top story bathrooms will be ducted through the attic to the outside through the roof or wall. Fans in bathrooms in the first story of a multi-story home are vented through the side of the house. 
  • If you are replacing or upgrading a fan, the diameter of the duct connector on the new housing may be larger than the size of your existing duct. To maximize performance, try to match your duct diameter to the new fan.