We often get this question from our clients that “How Many CFM Do I Need” for my house. CentricAir recommends that clients consider purchasing the largest whole house fan that their home has the attic ventilation for. It’s very likely for example that a 2200 sq. ft. home will have sufficient attic ventilation for our CentricAir 2.7 model which requires about 3.25 sq. ft. of net free attic ventilation. However, if this same size home has enough attic ventilation for our CentricAir 3.4 system which is designed for homes with 4.0 sq. ft. of net free attic ventilation, this may be worth considering since it’s only slightly more expensive and will cool your home even faster. We do not, however, recommend adding additional roof ventilation just to go with a large whole house fan.