| Installing and Using a Whole House Fan
Why Use a Whole House Fan?
A whole house fan is a simple and inexpensive method of cooling a house. 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 conditioning. Outside air temperature and humidity dictate times 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.
First cost benefit
Equipment cost for whole house fan = $150—$350
Equipment cost for window unit AC = $250—$750
Equipment cost for central AC = $2,000—$4,000
Ventilation
A whole house fan can be used to change the air in the house and vent odors quickly.
Economics of operation
Operating a properly sized 2-ton, 10 SEER air conditioner in Atlanta, Georgia costs over $250 per cooling season (1250 hours), based on 8.5¢/kwh, or roughly 20¢ 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, the whole house fan has a motor in the 1/4 to 1/2 hp range, uses between 120 to 600 watts, and costs around 1¢-5¢ per hour of use.
What Are The Drawbacks?
Temperature, humidity, and dust
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.
Maximize Your Savings
During the winter months (and summer when air conditioning is used), a whole house fan represents a potential energy loss because it is essentially a large, uninsulated hole in the ceiling. Standard fan louvers do not insulate or seal tightly.
Build and use fan covers
Because the louvers are leaky, a cover should be constructed to airseal and insulate this hole during the seasons when the fan is not in operation. The cover may be installed from the attic side if attic access is easily available or from the house side. Both covers could be included in excessively hot or cold climates. Homeowners must remember to remove cover(s) before operating the fan and to replace cover(s) during seasons when the fan is not in use.
Cooling Strategies
In the summertime, the air inside a home is heated during the hot part of the day. At night especially, and 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 open all or at least several windows, even if only partially, to provide 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 fan. The cool room materials (along with ceiling or circulating fans which create an additional cooling effect) will help keep the interior more comfortable.
Installing a Whole House Fan
See diagram for construction details.
How to build an attic-side box cover
A typical whole house fan has a 30" diameter blade with a sheet metal cowling of 31" to allow for blade clearance. An attic-side box cover may be constructed from a 4' x 4' piece of 1" rigid fiberglass duct board. The box will be 33" square with 1" thick walls (inside dimension of 31" x 31"). It will be 6½" deep. Adjust dimensions to actual fan size.
Attic-side box cover materials list:
- 48" x 48" piece of 1" fiberglass duct board
- Silver duct tape or house wrap tape
- Tools; measuring tape, straight edge, utility knife
- Permanent marker to label box
- Wear gloves and eye protection when working with duct board
Use "H" Brackets To Provide Proper Support
When installing a whole house fan, be sure to provide proper support and seal the unit into the rough opening in the ceiling. Never cut a truss chord; wooden "H" brackets installed between the trusses create a framed box to raise the fan above the truss system. The louvers must be able to operate freely (open/close) and care must be undertaken to prevent binding or misalignment.
Helpful Reminders
Attach labels to remind users to remove energy-saving covers.
- Label the attic-side box cover
- "WHOLE HOUSE FAN COVER,"
- "REMOVE BEFORE OPERATING FAN,"
- "REPLACE WHEN NOT USING FAN,"
- Label the fan switch
- "LABEL THE SWITCHES WITH NAMES"
Selecting a whole house fan
Fan speed
Two-speed fans permit the entire house to be ventilated quickly on high speed (such as when the occupants first arrive at home) and then provide gentle air circulation at the lower, quieter speed. Variable speed units offer more flexibility in selecting the desired air movement.
Control options
Controls may be simple on/off pull or wall switches, multi-speed rotary wall switches, or a timer which automatically shuts off the fan at pre-selected time intervals.
Louvers
Dampers or louvers typically operate automatically whenever the fan operates. Motorized dampers are available but are not necessary if the louvers are correctly installed and maintained. Proper opening and closing of louvers is critical to a whole house fan's performance.
Motor mounts and noise
A direct drive unit has its fan blades attached directly to the motor's shaft. It is usually less expensive to buy and operates at higher rpm's than its belt driven counterpart. A belt driven unit, which typically features a motor driving a slower moving, larger diameter fan with four or more blades, may be quieter, but will require maintenance of the pulley and belt.
In addition to sizing a whole house fan correctly, it is important that ALL penetrations between the attic and living space are sealed and that the attic is properly ventilated. A central hallway, or a stairway in a two-story house, is the most common location.
 Sizing A Whole House Fan
Determining the amount of airflow in cubic feet per minute (cfm) that the whole house fan should provide involves a simple calculation. Multiply the total gross square footage of the house (include upstairs area) by the ceiling height (typically 8 feet). Select a fan that delivers between one half to one times that amount of cfm at 0.1" static pressure. For example, a 25'x40', one-story home is 1,000 square feet and would need an 8 x 1,000 x 0.5 = 4,000 cfm fan or better. A manufacturer sells a two-speed unit that delivers 4,500 cfm at the high setting (240 watts) and 3,200 cfm at low (120 watts); this unit should be adequate.
Installation tips and concerns
Seal penetrations and vent attic adequately
Caulk all penetrations between the attic and living space, i.e., electrical boxes for ceiling light fixtures, loose attic hatches, large cutouts for plumbing vents, exposed beams, and recessed lights. A whole house fan creates a positive pressure in your attic and it is important that air from the attic is not forced back into the living space through cracks and gaps.
Guidelines for sufficient attic vent area is one square foot of net free vent area per 750 cfm of fan airflow, (4,500 / 750 = 6 square feet for the example above). Continuous ridge and soffit vents are usually more than adequate. Vents with insect screens may have a net free area equivalent to ½ of the total open area depending upon the size of the holes in the screen area. Insulation should be installed directly against the fan box frame. Blown-in insulation may require the sides of the fan box to be raised (with baffles) to prevent interference.
Avoid backdrafts
Care should be taken to avoid backdrafting combustion appliances that are installed in the conditioned space. It is strongly recommended that combustion appliances NOT be installed in such a manner that they use room air for combustion. The whole house fan is capable of pulling large quantities of air from the home and, particularly if not enough windows are open, may easily backdraft a water heater located inside a louvered closet door.
Label your switches
Controls should be placed higher on walls than light switches to avoid confusion and to keep them out of the reach of small children. Labels over switches are recommended to remind users to remove any energy-saving covers and to open at least two or morewindows before using.
Prepared for U.S. Department of Energy by Southface Energy Institute,
Oak Ridge Laboratory,
Florida Solar Energy Center, and National Association of Home Builders Research Center.
For more information contact:
Energy Efficiency and Renewable Energy Clearinghouse (EREC),
800-DOE-EREC,
P.O. Box 3048,
Merrifield,
VA 22116-0121,
www.eren.doe.gov or:
Southface Energy Institute,
241 Pine St.,
Atlanta,
GA 30308,
404-872-3549,
www.southface.org
Source List
The following organizations and publications provide more information on hot-water energy efficiency. Much of the information included in this publication was obtained from several of these sources. This list does not cover all the available books, reports, and articles on hot-water energy efficiency, nor is the mention of any publication to be considered a recommendation or endorsement. To obtain the publications in this list, contact your local library or bookstore or the publisher. Check publication prices through your bookstore or the publisher before placing an order.
American Council for an Energy-Efficient Economy (ACEEE)
1001 Connecticut Avenue, NW, Suite 801
Washington, DC 20036
(202) 429-8873
Email: info@aceee.org
ACEEE provides general and technical information on energy efficiency, including these publications: The Consumer Guide to Home Energy Savings, The Most Energy-Efficient Appliances, and Saving Energy and Money with Home Appliances. These and other publications can be ordered by calling 202-429-0063.
Association of Home Appliance Manufacturers (AHAM)
1111 19th St., NW, Suite 402
Washington, DC 20036
(202)872-5955
Fax: (202)872-9354
AHAM provides energy efficiency information for specific brands of major appliances. The association also runs a certification program for certain types of appliances.
Gas Appliance Manufacturers Association, Inc. (GAMA)
2107 Wilson Boulevard, Suite 600
Arlington, Virginia 22201
(703) 525-7060
Fax: (703) 525-6790
Email: information@gamanet.org
GAMA has information on residential gas appliances and equipment, electric and oil-fired water heaters, and oil-fired warm air furnaces.
Energy Information Administration (EIA)
U.S. Department of Energy
EI-231, Room 1F-048
Forrestal Building
Washington, DC 20585
(202) 586-8800
Email: infoctr@eia.doe.gov
EIA compiles a wide range of statistics for the energy professional on energy sources and energy consumption. EIA s Household Energy and Consumption and Expenditures contains information on residential energy use.
Further information about energy-efficient water heating can be obtained by contacting:
Ask an Energy Expert
The Energy Efficiency and Renewable Energy Clearinghouse (EREC)
P.O. Box 3048
Merrifield, VA 22116
(800) DOE-EREC (363-3732)
Fax: (703) 893-0400
E-mail: doe.erec@nciinc.com
Consumer Energy Information Web site
Energy experts at EREC provide free general and technical information to the public on the many topics and technologies pertaining to energy efficiency and renewable energy.
Also contact your state and local government energy offices and utility for additional information on energy-efficient water heaters, installation, and rebate or incentive programs.
Reading List
Books and Reports Consumer Reports 1992 Buying Guide Issue,
Consumers Union of the United States, Inc.,
101 Truman Avenue, Yonkers,
NY 10703-1057,
December 1991.
The Water Heater Workbook: A Hands-on Guide to Water Heaters, published by Elemental Enterprises, P.O. Box 928, Monterey, CA 93942, 1992.
The Water Heater Workbook:
A Hands-on Guide to Water Heaters, published by Elemental Enterprises,
P.O. Box 928,
Monterey,
CA 93942, 1992.
"Water Heating," Energy Edge, Pennsylvania Energy Office, 116 Pine Street, Harrisburg, PA 17101 (printed by DOE).
"An Investigation of Off-Peak Domestic Hot Water Heating," ASHRAE Journal, p. 32, January 1990.
"Dishwashers," Consumer Reports, p. 637, October 1993.
"Hot Water Energy Conservation: Heating Water Accounts for 15% to 25% of an Average Family s Energy Budget," Consumers Research Magazine, p. 19, January 1991.
"Safer Water Filters, Cheaper Water-Heating Systems, and More," Home Mechanix, p. 37, June 1993.
"Showering Them With Gas," American Gas, p. 22, April 1989.
|
|
 |
