The actual physical size of a whole house fan matters much less than most would realize. The size of the grille or the fan does not contribute much to the effectiveness of the fan. CFM is far more important to how the whole house fan works.
The general rule is for a “good” system, you want 2 CFM per square foot of living space, for a “better” system, you want 2.5 CFM per square foot of living space, and for the “best” system, you want 3 or more CFM per square foot of living space. However, CFM is not the physical size of a fan but how powerful the fan is. It is a measurement of the velocity at which air flows into or out of a space. The CFM measurement often is used in reference to a computer’s cooling system.
The actual physical size of a whole house fan is dependant on what whole house fan you get. Most grilles, which is the rectangular or circular part of a whole house fan which holds the actual spinning blades usually sits around sixteen by sixteen inches to sixteen by thirty eight inches.
On Quiet Cool fans, this is not the only sizable aspect of a whole house fan. Quiet Cool fans also have a long tubular venting system that is usual around two to four feet. This long self-contained duct system hangs in the attic to help neutralize the sound and noise vibration heard in the home. The result is zero noise vibration allowing the system to be used in the home without disturbing anyone who may be sleeping or if someone is working from their home.
Quiet Cool fans then also have a R5 insulated damper system. This rectangular box at the opposing end of the duct system is also about sixteen by sixteen inchies and includes barometric pressurized gravity dampers that insure there will be no heat/cooling loss between the home and attic. Compare this to traditional whole house fans that have old‐style shutters with zero R‐Value and the Quiet Cool system is far superior.
So, unlike most other whole house fans, Quiet Cool whole house fans are slightly larger. This is not a bad thing, however.. The duct system is flexible while the actual fan and damper system plug right in the walls. Because of this, even those with a smaller attic would not have trouble installing a whole house fan.
Adding all of these features together equates to about five feet total. Most every attic has at least five feet of space and the actual physical size of these cooling systems actually does not matter so much.