A properly sized attic fan is very important to ensure the most effective and efficient ventilation of your attic.
We recommend sizing your attic fan at .5 CFM per square foot of attic space for every 2 feet of peak attic height. This formula gives a minimum of 15 complete air exchanges per hour.
This means for a 1500 SQFT attic with a peak attic height of 4 feet, you will need an attic fan that moves at least 1500 CFM. If the peak attic height is only 2 feet, you would need at least 750 CFM. If the peak attic height is 6 feet, you would need at least 2250 CFM, and so on.
This math formula will work every time, for any size attic, and as always the more airflow the better.
This sizing formula provides a minimum of 15 complete air exchanges per hour which is equivalent to the sizing formula we use for our whole house fans.
Note that this sizing formula is based on attic square footage, not the square footage of the home. While in some cases they may be the same value, such as with a single story home, multi-story homes will have a different attic square footage than the home.
If you need assistance with sizing an attic fan, use our Attic Fan System Builder below.
