QuietCool | Frequently Asked Questions

16. What is a whole house fan and how does it cool?
A WHOLE HOUSE FAN is a large fan mounted in a venturi housing and is installed in the attic. They are used to both cool and ventilate a house.

A whole house fan is able to cool your house in 3 ways:
   1.   They draw cooler outside air in through your open windows which lowers the room temperature by as much as 10 to 20 degrees F. Your open windows serve as intake “vents” which allow you to control the air flow by selecting how many or which windows you open.
   2.   The moving air blowing through the house cools the occupants. The cooling breeze can lower the skin temperature by 5 to 10 degrees F.
   3.   The cooler air, after passing through the living space, is forced into the attic which pushes the hot attic air out through the attic vents. This can lower the attic air temperature by as much as 40 degrees F. The attic can reach temperatures in excess of 150 degrees F. in summer, and that air, if allowed to remain undisturbed, will radiate heat down through the insulation to heat the living space. That is the main reason that a home, without the use of a whole house fan, remains uncomfortably warm in summer evenings, and that the upper floor of a multi-floor house is always warmer.

Whole house fans are rated according to the amount of air they can move. This is measured in cubic feet of air per minute, or CFM. In order to be effective, a whole house fan’s CFM rating should be 2 to 3 times the square footage of the house. For example, a 1,500 square foot house should have a whole house fan system capable of 3,000 to 4,500 CFM.

Overall attic venting is the only limiting factor on how many CFM can be efficiently moved. However, attic venting can be easily increased. Too many CFM for the attic venting can cause undue stress on the whole house fan and pressurizes the attic and walls. Too little CFM will not provide the desired minimum of 10 air exchanges per hour as recommended by the House Ventilation Institute, and may not provide the cooling draft to lower house, attic, and skin temperatures in a timely fashion.

See our Ventilation page explaining why proper ventilation is so important.