Bathroom Size Matters

By Becca Lucio

Properly sizing your fan is important to ensure that proper ventilation is used for your bathroom. Are you experience a buildup of fog post shower and a lingering mildew scent? It might be time to resize your fan to handle your needs. Follow the helpful tips below.

Fan Sizing for Bathrooms Under 100 Square Feet

The standard rule for bathrooms 100 square feet or smaller is one CFM per square foot of the bathroom. To find the square footage, multiply the length of the bathroom by the width.


Fan Sizing for Bathrooms Over 100 Square Feet

Ventilation for baths over 100 square feet is calculated based on the fixtures in the bathroom (see table below). Add the CFM of all fixtures within the bathroom for the required fan CFM.


Note: Enclosed toilet rooms must have an operable window or a fan for ventilation.


Two Solution Options:

  1. Install a 100 CFM fan over the tub, 50CFM fan in the shower and above the toilet. This method will provide ventilation where and when it’s needed.
  2. Install one 200 CFM fan. The air will be pulled through the entire room and exhausted at a central location.

For more information on bath fan sizing and ventilation, visit

Tags: Residential