Whole House Attic Fan
Outside air temperature and humidity dictate when the whole house fan would be
favorable over air conditioning. If both methods of cooling are present, a seasonal use of
the whole house fan (during spring and fall) may yield the optimum combination of
comfort and cost.
What Are The Drawbacks?
A whole house fan has some drawbacks: the fan can only cool the inside of a house to
the outside temperature; unlike an air conditioner, it does not dehumidify; and dust and
pollen can be brought into the house.
Economics of Operation
Operating a properly sized 2-ton, 10 SEER air conditioner in Atlanta, Georgia for example
costs over $280 per cooling season (1250 hours), based on 9.5¢/kwh, or roughly 22¢ per
hour of runtime.
A large 18,000 Btu/hr window unit air conditioner with a 6 EER costs more than 25¢ to
operate for one hour.
By contrast, whole house fans have motors in the 1/4 to 1/2 hp range that use between
120 to 600 watts and cost only 7¢ per hour of use for the most powerful fans.
What Size Fan Do I Need?
Whole house fans are rated by the number of cubic feet per minute (cfm) of air they
exhaust from the building. The HV1600 fan shown below is rated at 1,600 cfm and would
change the air in a 1,000 square foot home approximately once every 5 minutes; a 1,500
sq ft home every 7 1/2 minutes; and a 2,000 sq ft home every 10 minutes.
The Home Ventilation Institute recommends one complete air change every two minutes
within the occupied area. This is unrealistic since it would require either one very large,
noisy, and expensive fan, or multiple smaller fans installed in the ceilings of individual
A more sensible approach for most homes is to opt for a single unit with moderate air
flow. The most popular whole house fans shown below will satisfy most home owner's
desire for relatively quick cooling with a minimum of noise and expense.
During the morning and late evening, the outside air is often cooler and can be used to
replace the inside air. It is important to partially open several windows to ensure
adequate airflow. Closing windows in unused rooms will create higher velocity air
movement in occupied rooms.
Running the whole house fan whenever outdoor temperatures are lower than indoor will
cool the house. Operate the whole house fan throughout the evening to cool interior
materials. An approximate rule of thumb would be to use the whole house fan when
outside temperatures are below 85°F.
As daytime temperatures rise, turn off the whole house attic fan. The cool room materials
(along with ceiling or circulating fans which create an additional cooling effect) will help
keep the interior more comfortable.
Attic Aire 54301 Whole House Fan Rated for 1,500 Sq. Ft.
* Direct-drive whole house fan with shutter
* Two speed operation - pull-chain switch
* Heavy steel housing
* Durable powder-coated finish
* Can be mounted without cutting attic joist
A whole house attic fan is a
relatively inexpensive and easy
to install option for cooling your
The fan draws cool outdoor air
inside through open windows
and exhausts hot room air
through the attic to the outside.
The result is excellent ventilation,
lower indoor temperatures, and
improved evaporative cooling.
What Are The Benefits?
A whole house fan can be used
as the sole means of cooling or
to reduce the need for air