AeroPure Fans has a square footage calculator available to assist our customers in answering this question. You can also use the following calculations: For an 8 ft ceiling take the square footage of the room and multiply by 1.1 (ex. 10’ x 10’ room with 8’ ceilings = 10’ x 10’ x 1.1 = 110 CFM’s) For anything over 9 ft, take the height of the ceiling and multiply by .13 **Both calculations will give you the minimum amount of CFM’s needed**