Buildings for

the 21st Century

Buildings that are more

energy-efficient, comfortable,

and affordable . . . that’s the

goal of DOE’s Office of Building

Technology, State and

Community Programs (BTS).

To accelerate the development

and wide application of energy

efficiency measures, BTS:

• Conducts R&D on technologies and concepts for energy

efficiency, working closely

with the building industry

and with manufacturers of

materials, equipment, and

appliances

• Promotes energy/money

saving opportunities to both

builders and buyers of homes

and commercial buildings

• Works with State and local

regulatory groups to improve

building codes, appliance

standards, and guidelines for

efficient energy use

• Provides support and grants

to States and communities

for deployment of energyefficient technologies and

practices

T e c h n o l o g y F a c t S h e e t

OFFICE OF BUILDING TECHNOLOGY, STATE AND COMMUNITY PROGRAMS

ENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY

E CONOMICS O F OPERATION

• Operating a properly sized 2-ton air

conditioner with a seasonal energy

efficiency ratio (SEER) of 10 in Atlanta,

Georgia, costs over $250 per cooling

season (1,250 hours), based on

8.5¢/kWh, or roughly 20¢ per hour

of runtime.

• A large 18,000 Btu/h window unit air

conditioner with an energy efficiency

ratio (EER) of 8.8 costs more than 17¢

to operate for one hour.

• By contrast, a whole house fan has a

motor in the 1

/

4

 to 1/

2 hp range, uses 120

to 600 watts, and costs around 1¢ to 5¢

per hour of use.

MAXIMIZE YOUR SAVINGS WITH

FAN COVERS

During the winter months (and in 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. Since standard fan louvers do not insulate or seal tightly, a cover should be constructed to airseal and insulate this hole (see

diagrams on pages 2 and 3 for construction

details). The cover may be installed from the

attic side (if attic access is easily available) or

from the house side. Covers for both sides

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.

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 indoor air through the attic to the

outside. Running a whole house fan whenever

outdoor temperatures are lower than indoor

temperatures will cool a house.

In summer, the air inside a home is heated

during the hot part of the day. During the

morning, late evening, and night, the outside

air is often cooler and can be used to replace

the inside air. Operating the whole house fan

at these times will cool interior materials. As

daytime temperatures rise, the whole house fan

can be turned off. The cool materials (along

with ceiling or circulating fans, which create an

additional cooling effect) will help keep the interior more comfortable.

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. If both methods of cooling are

present, seasonal use of the whole house fan

(during spring and fall) may yield the optimum

combination of comfort and cost.

I NITIAL 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

WHOLE HOUSE FAN

How to install and use a whole house fan
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INSTALLATION TIPS

AND CONCERNS

SEAL PENETRATIONS AND VENT

ATTIC ADEQUATELY

Caulk all penetrations between the

attic and living space, such as

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 the attic; it is important

that air from the attic is not forced

back into the living space through

cracks and gaps.

A guideline 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 described on page 4).

Continuous ridge and soffit vents

are usually more than adequate.

Vents with insect screens may have

a net-free area equivalent to one-half

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.

INSTALLING A WHOLE

HOUSE FAN

Louver Cover Materials List

• 30" x 30" piece of 3

/

4

"–1" rigid insulation (minimum thickness)

• White contact paper

• Drill with 1/

4

" bit

• 11

/

4

" long, 1/

4

"- 20 threaded bolt

• Fender washer with 1/

4

" opening

• 1/

4

"- 20 wing nut

• VelcroTM with adhesive fasteners

a a a a a a a a aaa

1

/

4

"-20 nut threaded all the

way up to hold bolt to the

louver section. Wing nut

and washer hold

rigid board insulation

tightly against louver.

LOUVER COVER DETAILS

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US E “ H” BRACKETS T O 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 open

and close freely and care must be taken to prevent binding

or misalignment. A fan with a 34" base (30" blade) will work

with the dimensions shown in the diagram at left.

B UILD A N 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

61/

2

" 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

• Note: Wear gloves and eye protection when

working with duct board

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. A 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.

WHOLE HOUSE FAN

“H” BRACKETS

ATTIC-SIDE BOX COVER
WHOLE HOUSE FAN

For more information,

contact:

Energy Efficiency and

Renewable Energy

Clearinghouse (EREC)

1-800-DOE-3732

www.eren.doe.gov

Or visit the BTS Web site at:

www.eren.doe.gov/buildings

Written and prepared for

the U.S. Department of

Energy by:

Southface

Energy Institute

404-872-3549

www.southface.org

Oak Ridge

National Laboratory

Buildings Technology Center

423-574-5178

www.ornl.gov/btc

NOTICE: Neither the United

States government nor any

agency thereof, nor any of their

employees, makes any warranty,

express or implied, or assumes

any legal liability or responsibility

for the accuracy, completeness,

or usefulness of any information,

apparatus, product, or process

disclosed. The views and opinions

of authors expressed herein do

not necessarily state or reflect

those of the United States government or any agency thereof.

SELECTING A WHOLE HOUSE FAN

FAN SPEED

A two-speed fan permits the entire house

to be ventilated quickly on high speed

(such as when the occupants first arrive

at home) and then provides gentle air

circulation at the lower, quieter speed.

A variable speed unit offers more flexibility

in selecting the desired air movement.

CONTROL OPTIONS

Control may be a simple on/off pull or wall

switch, a multi-speed rotary wall switch,

or a timer that automatically shuts off the

fan at pre-selected time intervals.

LOUVERS

Dampers or louvers typically operate

automatically whenever the fan is on.

Motorized dampers are available but are

not necessary if the louvers are correctly

installed and maintained.

MOTOR MOUNTS AND NOISE

A direct drive unit has its fan blades

attached directly to the motor shaft. This

type of unit is usually less expensive to

buy and operates at a higher speed than its

belt-driven counterpart. A belt-driven unit

typically features a motor driving a slowermoving, larger-diameter fan with four or

more blades. It may be quieter, but will

require maintenance of the pulley and belt.

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

time that amount of cfm at 0.1" static pressure.

For example, a 25' x 40' one-story home is

1,000 square feet and would need an 8 x

1,000 x 1/

2

 = 4,000 cfm fan or better. A

two-speed unit that delivers 4,500 cfm at the

high setting (240 watts) and 3,200 cfm at low

(120 watts) should be adequate.

HELPFUL REMINDERS

Label the attic-side box cover and the fan

switch to remind users to remove energysaving covers. Instruct occupants to open at

least two or more windows before operation,

especially windows in occupied rooms where

cooling is desired.

WHOLE HOUSE FAN AIR FLOW

In addition to sizing a whole house

fan correctly, it is important to ensure

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.

Printed with a renewable-source ink on paper containing at

least 50% wastepaper, including 20% postconsumer waste.

March 1999 DOE/GO-10099-745