ComfortCool Fans recommends 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. two story home will have sufficient attic ventilation for our 2.7 model which requires about 3.25 sq. ft. of net free attic ventilation. However, if this same size home has enough ventilation for our 3.1 model which requires 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 system.