Some whole house fan companies are overstating the CFM (cubic feet of air per minute) of their whole house fan by only providing the rating of the fan “Free Standing.” Free Standing is when the airflow is measured before the fan is connected to the ducting, damper and grill. The Real CFM is the rating of the fan when it’s connected to the rest of the system (the ducting, damper and grill); this is the correct way to measure the airflow of a modern whole house fan. The Real CFM can be as much as 40% to 50% less than the Free Standing CFM. Comfort Cool Fans is one of the few ducted whole house fan companies that have been certified to the California Energy Commission as HVI-916 energy efficiency standards.
Attic Ventilation (Beware of “one size fits all” whole house fans)
A whole house fan pulls air into the home through open windows and doors and ultimately all that air is blown into the attic. As a result, it’s important that there is adequate attic ventilation to properly exhaust the amount of air that is blown into the attic. If there is not sufficient ventilation, you can over pressurize the attic causing hot, dirty attic air to be blown back into the home and the fan to fail prematurely.