On mild days and evenings, I like to open windows to get fresh, cool air into my house. Would using a whole-house fan draw the air in quicker? Do these fans use much less electricity than my central air conditioner?—Gary W.
With today’s airtight, energy-efficient homes, it is nice to bring in cool outdoor air whenever possible without driving up your utility bills. Using a whole-house fan is probably the most effective and efficient means to quickly cool your home when the outdoor temperature drops overnight or on moderately warm days.
(Editor’s note: Effective use of a whole-house fan requires attention to ventilation and insulation issues: (1) make sure your attic is well-ventilated, as many are not, or use of the fan could cause problems such as air infiltrating back into the house, backflows through the ducts, or even shifting the insulation, and (2) the fan needs to be closed up and insulated during the winter or you could lose all the energy savings you made during the summer.)
A whole-house fan is a large exhaust fan usually mounted in the attic floor. It is often located in a hallway ceiling to draw air from the entire house without creating drafts in the rooms. Since it is most often used at night, this location minimizes the noise level in the bedrooms. The fan draws outdoor air in through opened windows and exhausts the air into the attic and out the attic vents.
A secondary benefit of using a whole-house fan is that the airflow from the house into the attic helps cool the attic and the roof. A hot attic and roof can radiate heat down through the attic insulation.
Using reflective attic foil stapled underneath the roof is a good combination with a whole-house fan. The foil will block the heat from the super-hot roof during the day. When you switch the fan on in the evening, the air is exhausted up between the foil and the roof to cool it.
Running a whole-house fan uses about 80 to 90 percent less electricity than operating a central air conditioner. Since your air conditioner is used less, less maintenance is needed and its life will be longer.
Whenever the outdoor temperature drops to about five degrees lower than your thermostat setting, running the whole-house fan should comfortably cool your house. This means you may run your central air conditioner during the daytime and run the whole-house fan at night.
There are many whole-house fan designs with various features from which to choose. For most average-sized homes, a direct-drive design is a good and easy-to-install choice. It has the motor located in the center of the housing with the fan blades attached directly to the motor shaft. The quietest models use vibration-blocking rubber hubs and sound-absorbing airflow shrouds to reduce the noise level to a whisper.
For larger houses that require a higher airflow, a belt-drive model is often used. With this design, the motor is mounted on the corner of the housing frame. A belt runs from a pulley on the motor to a pulley on the fan blade hub. With the motor out of the airflow path and a larger unobstructed blade diameter, the airflow can be greater. These often use a steeper blade pitch and run at a lower speed to further reduce the noise level.
When sizing a whole-house fan, a good rule of thumb is the airflow rating in cubic feet per minute should be three times the house size in square feet. If you choose a model with two or variable speeds, you can install a larger, higher capacity fan. This will allow you to run it on high speed initially to quickly cool your house and then set it to the correct continuous speed.
Write for Utility Bills Update No. 641 for a buyer’s guide of 28 whole-house fan models . Include $3.00, a business-size SASE, and Update number. Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to www.dulley.com to instantly download.