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Real CFM vs Free Standing CFM & The Importance of Proper Attic Ventilation


CAUTION: Some whole house fan manufactures are overstating the CFM (Cubic Feet of Air Per Minute) of their whole house fans by providing the rating of the fan “Free Standing.” Free Standing is when the CFM is measured before the fan is connected to the ductwork, damper box and register.  The Real CFM is the rating of the fan when it’s connected to the entire system (the ductwork, damper box and register); this is the proper way to measure the CFM. The Free Standing CFM can be as much as 40 to 50 percent more than the “Real CFM.”  Comfort Cool, Inc is one of the few ducted whole house fan companies that have been certified to the California Energy Commission as meeting the strict HVI-916 energy efficiency standard.

Attic Ventilation (Beware of “one size fits all” whole house fans)

Whole house fans pull air into the house through open windows or doors and ultimately all that air is blown into the attic. For this reason, it’s important that there is sufficient attic ventilation to properly exhaust the amount of air that is blown into the attic. If there is not enough venting, you can over pressurize your attic causing hot dirty attic air to be blown back into the home and the fan to prematurely fail. All CentricAir whole house fans list the required amount of attic ventilation.

PG&E Logo PG&E provides additional information on ventilation requirements, installation, and safety. Click on the PG&E image for more information.