You can save energy and money when

you ventilate your home instead of using

your air conditioner, except on the hottest

days. Moving air can remove heat from

your home. Moving air also creates a wind

chill effect that cools your body. 

Ventilation cooling is usually combined

with energy conservation measures like

shading provided by trees and window

treatments, roof reflectivity (light-colored

roof), and attic insulation. Mechanical air

circulation can be used with natural ventilation to increase comfort, or with air conditioning for energy savings.

Ventilation provides other benefits besides

cooling. Indoor air pollutants tend to accumulate in homes with poor ventilation, and

when homes are closed up for air conditioning or heating. 

Principles of Cooling

Cooling the Human Body 

Your body can cool down through three

processes: convection, radiation, and perspiration. Ventilation enhances all these

processes.

Convection occurs when heat is carried

away from your body via moving air. If the

surrounding air is cooler than your skin,

the air will absorb your heat and rise. As

the warmed air rises around you, cooler air

moves in to take its place and absorb more

of your warmth. The faster this convecting

air moves, the cooler you feel.

Radiation occurs when heat radiates

across the space between you and the

objects in your home. If objects are

warmer than you are, heat will travel

toward you. Removing

heat through ventilation reduces the temperature of the ceiling,

walls, and furnishings.

The cooler your surroundings, the less

heat you’ll attract, and

the more of your own

excess heat you’ll lose. 

Perspiration can be

uncomfortable, and

many people would

prefer to stay cool

without it. However,

during hot weather

and physical exercise,

perspiration is the

body’s powerful cooling mechanism. 

Cooling Your Home 

with Fans and Ventilation

This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. The

document was produced by the Information and Outreach Program at NREL for the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on

information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC.

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

DOE/GO-102001-1278

FS228

June 2001

Ceiling fans distribute cool air, making cooling equipment 

more efficient.
As moisture leaves your skin pores, it carries a lot of heat with it, cooling your

body. If a breeze (ventilation) passes over

your skin, that moisture will evaporate

more quickly, and you’ll be even cooler. 

How Heat Accumulates 

Heat accumulates in homes from several

sources and can make indoor temperatures higher than outdoors even in the

hottest weather. Solar energy—which

enters a home primarily through the roof

and windows—is a major source of

unwanted heat in most climates. Appliances, lights, and occupants generate heat

as well.

To use ventilation instead of air conditioning for cooling, you should prevent heat

from entering and accumulating in your

home as much as possible. Some preventive measures include installing additional

attic insulation, a reflective roof, awnings,

and sun-blocking window treatments.

Operational changes—such as reducing

the use of appliances, lighting, and hot

water—will also reduce accumulated heat.

When you’ve prevented as much heat

accumulation as you can, develop a ventilating strategy.

Natural Ventilation

Natural ventilation relies on the wind and

the “chimney effect” to keep a home cool. 

The wind will naturally ventilate your

home by entering or leaving windows,

depending on their orientation to the

wind. When wind blows against your

home, air is forced into your windows.

Heat accumulates in your home during

the day, and the cool night air can flush it

out. For drier climates, this will mean ventilating at night, and closing doors, windows, and window coverings during the

day. This may not apply in humid climates. Depending on the house design

and wind direction, a windbreak—like a

fence, hedge, or row of trees that blocks

the wind —can force air either into or

away from nearby windows. Wind moving along a wall creates a vacuum that

pulls air out of the windows. 

The chimney effect occurs when cool air

enters a home on the first floor or basement, absorbs heat in the room, rises, and

exits through upstairs windows. This creates a partial vacuum, which pulls more

air in through lower-level windows.

Natural ventilation works best in climates

with cool summers or cool nights and regular breezes.

Using Windows and Doors for 

Cross-Ventilation

You can create natural cross-ventilation 

by opening your windows and doors, and

adjusting the size and location of the openings to ventilate different parts of the home. 

Inlets and outlets located directly opposite

each other cool only those areas in

between, in the direct path of the airflow.

You'll cool more of your home if you force

the air to take a longer path between the

inlet and outlet. Use smaller window

openings for the inlets and larger openings for the outlets. This increases air

speed and improves the cooling effect. 

Air from cooler, shaded outdoor areas 

provides the best intake air.

Experiment with different patterns of window venting to move fresh outside air

2

Install additional attic

insulation,

a reflective roof, 

and sun-blocking

window treatments.

Fig. 1 Use windows and doors for cross-ventilation.
3

Circulating fans create a wind chill effect

to make you more

comfortable.

through all the living areas of your home.

This may involve leaving some windows

closed if they interfere with air moving

along a longer path through the home. 

Attic Ventilation

Solar heat travels in through the roof and

radiates into the attic. Attic ventilation

reduces attic temperature 10 to 25 degrees

and slows the transfer of heat into the 

living space. However, the most effective

way to reduce attic heat is to prevent it

from entering in the first place with a

reflective roof. Also very important is

having at least a foot of attic insulation.

Mechanical Ventilation

When you know how air moves naturally

through your home, you can then optimize your mechanical ventilation.

In warmer climates, natural ventilation

can’t circulate enough air through a home

to provide sufficient cooling at night to

remove the day’s heat. Mechanical ventilation can provide continuously moving air

that will keep your home cooler, day and

night, with circulating fans, whole-house

fans, and/or evaporative coolers. 

The quality and energy efficiency of these

devices varies widely. Shop carefully—it

might be best to buy from a dealer who

specializes in fans rather than from a

department store.

Circulating Fans 

Circulating fans include ceiling fans, table

fans, floor fans, window fans, and fans

mounted to poles or walls. These fans create a wind chill effect that will make you

more comfortable in your home, even if

it's also cooled by natural ventilation or air

conditioning.

Ceiling Fans

If you use air conditioning, a ceiling fan

will allow you to raise the thermostat setting about 4 ̊F with no reduction in comfort. In temperate climates, or during

moderately hot weather, ceiling fans may

allow you to avoid using your air conditioner altogether.

Install a fan in each room that needs to be

cooled during hot weather. Fans work best

when the blades are 7 to 9 feet above the

floor and 10 to 12 inches below the ceiling.

Fans should be installed so their blades

are no closer than 8 inches from the ceiling

and 18 inches from the walls. 

Larger ceiling fans can move more air than

smaller fans. A 36- or 44-inch-diameter fan

will cool rooms up to 225 square feet,

while fans that are 52 inches or more

should be used in larger rooms. Multiple

fans work best in rooms longer than 18

feet. Small- and medium-sized fans will

provide efficient cooling in a 4- to 6-foot

diameter area, while larger fans are effective up to 10 feet.

A larger blade will also provide comparable cooling at a lower velocity than a

smaller blade. This may be important in

areas where loose papers or other objects

will be disturbed by a strong breeze. The

fan should also be fitted to the aesthetics

of the room—a large fan may appear overpowering in a small room.

A more expensive fan that operates 

quietly and smoothly will probably offer

more trouble-free service than cheaper

units. Check the noise ratings, and, if possible, listen to your fan in operation before

you buy it. 

Table fans provide refreshing breezes.
Window and Exhaust Fans 

Window fans are best used in windows

facing the prevailing wind or away from it

to provide cross-ventilation. Window fans

augment any breeze or create a breeze

when the air is still. If the wind direction

changes frequently in your area, use

reversible-type window fans so you can

either pull air into the home or push air

out, depending on which way the wind

blows. Experiment with positioning the

fans in different windows to see which

arrangement gives the best cooling effect.

In a larger house, consider installing a window fan that blows air in through a lowerlevel window in a cool area and another

window fan that blows air out through a

higher-level window in a hotter area. 

Use exhaust fans in the kitchen and bath

to remove heat and humidity when cooking and bathing. Larger, securely installed

exhaust fans can ventilate homes where an

open window would be a security issue.

Large exhaust fans can be mounted outdoors on a wall or roof to reduce indoor

noise.

Be cautious with these large exhaust fans.

If enough ventilation isn’t provided, the

fans can pull combustion products (e.g.,

carbon monoxide from furnaces or water

heaters) into your living space.

Whole-House Fans

A whole-house fan can substitute for an

air conditioner most of the year in most

climates. Whole-house fans combined

with ceiling fans and portable fans provide acceptable summer comfort for many

families, even in hot weather. 

How Whole-House Fans Work

The whole-house fan pulls air in from

open windows and exhausts it through

the attic and roof. It provides good attic

ventilation in addition to whole-house

ventilation. You can regulate cooling by

simply closing windows in the unoccupied areas and opening windows wide in

occupied areas. Many people cool the bedrooms at night and the living areas during

the daytime.

Whole-house fans should provide houses

with 30 to 60 air changes per hour (varies

with climate, floor plan, etc.—check with a

professional to determine what is appropriate for your home). The air-change rate

you choose depends on your climate and

how much you depend on the wholehouse fan for cooling. Cooler, shadier

areas don’t require as much ventilation as

warmer, sunnier ones. Houses entirely

dependent on whole-house fans require a

bigger fan because there is no air conditioning to fall back on.

Sizing a Whole-House Fan

Whole-house fans are sized in cubic feet

per minute (cfm) of ventilating power. To

determine the size you'll need, first calculate the volume of your house in cubic

feet. To do that, multiply the square

footage of the floor area you want to cool

by the height from floor to ceiling. Take

that volume and multiply by 30 to 60 air

changes per hour (depending on the

power you need). Then, divide by 60 minutes to get the cubic feet per minute of

capacity your house requires. [(Square

feet______ x room height______) x 30 or 60

/ 60 = cfm required _________. ]

4

A whole-house fan

can substitute for an

air conditioner most

of the year.

Fan Noise Levels

• When shopping for circulating fans, be

sure to test the fan for noise. Listen to

the different qualities of each fan’s

sound. Fans also will be marked with

their rated noise level, measured in

“sones.” Very quiet fans are rated at

1.5 sones. Some are so quiet, they’re

rated as low as 0.5 to 1 sones.

• Poor installation can affect a fan’s noise

level. If a fan isn’t installed securely, it

can vibrate and rattle, making as much

noise as a poorer-quality fan.

• Your fan will probably run for a good

part of the day – be sure it’s quiet as

well as cooling.
Installing and Using a Whole-House Fan

Installing a whole-house fan is tricky and

should be done by a professional. Attic

measurements, dedicated circuit wiring,

and possibly new attic vent installation

should be performed by an experienced

person.

Attic ventilation must be increased to

exhaust the fan’s air outdoors. You’ll need

2 to 4 times the normal area of attic vents,

or about one square foot of net free area

for every 750 cfm of fan capacity. The net

free area of a vent takes into account the

resistance offered by its louvers and insect

screens. More vent area is better for optimal whole-house fan performance. 

Some fans come with a tight-sealing winter cover (or you can build one). If you

switch between air conditioning and cooling with a whole-house fan as the summer

weather changes, build a tightly sealed,

hinged door for the fan opening that is

easy to open and close when switching

cooling methods.

Drawbacks of Whole-House Fans

Whole-house fans can be noisy, especially

if improperly installed. In general, a largecapacity fan running at low speed makes

less noise than a small fan operating at

high speed. All whole-house fans should

be installed with rubber or felt gaskets to

dampen noise. You can set a multispeed fan

to a lower speed when noise is a problem.

Evaporative Coolers

Evaporative coolers or swamp coolers are a

popular and energy-efficient cooling strategy in dry climates of the United States. 

Hot outside air enters the swamp cooler.

The air passes over water-saturated pads,

and the water evaporates into the air. The

energy used removes heat from the air.

The 15- to 40-degree-cooler air is then

directed into the home, and pushes

warmer air out through windows.

Because this process also humidifies the

air, swamp coolers are best used in areas

with low summertime relative humidity. 

Evaporative coolers use less than onethird the energy of air conditioners, and

cost about half as much to install. Unlike

5

Whole-house fans

should provide houses

with 30 to 60 air

changes per hour.

Fig. 2 A whole-house fan.
central air conditioning systems that recirculate the same air, evaporative coolers

provide a steady stream of fresh air into

the house.

Sizing and Selection

Evaporative coolers are rated by the cfm

of air that they deliver to the house. Most

models range from 3,000 to 25,000 cfm.

Manufacturers recommend providing

enough air-moving capacity for 20 to 40 air

changes per hour, depending on climate.

Installation 

Evaporative coolers are installed in one of

two ways: the cooler blows air into a central location, or the cooler connects to

ductwork, which distributes the air to different rooms. Central-location installations

work well for compact houses that are

open from room to room. Ducted systems

are required for larger houses with hallways and multiple bedrooms.

Most people install down-flow evaporative coolers on the roofs of their houses.

However, many experts prefer to install

ground-mounted horizontal units, which

feature easier maintenance and less risk of

roof leaks.

Small horizontal-flow coolers are installed

in windows to cool a room or section of a

home. These portable evaporative coolers

work well in moderate climates, but may

not be able to cool a room adequately in

hot climates. Room evaporative coolers

are becoming more popular in areas of the

western United States with milder summer weather. They can reduce the temperature in a single room by 5 to 15 degrees.

Operation

An evaporative cooler should have at least

two speeds and a vent-only option. During vent-only operation, the water pump

does not operate and the outdoor air is not

humidified. This lets you use the evaporative cooler as a whole-house fan during

mild weather. 

Control the cooler’s air movement

through the house by adjusting window

openings. Open the windows or vents on

the leeward side of the house to provide 

1 to 2 square feet of opening for each 1,000

cfm of cooling capacity. Experiment to

find the right windows to open and the

correct amount to open them. If the windows are open too far, hot air will enter. 

If the windows are not open far enough,

humidity will build up in the home. You

can regulate both temperature and humidity

6

Portable evaporative

coolers work well in

moderate climates.

Fig. 3 Evaporative cooling.
7

The new two-stage

evaporative coolers

are even more 

efficient.

by opening windows in the areas you

want to cool, and closing windows in

unoccupied areas. 

Where open windows create a security

issue, install up-ducts in the ceiling. Upducts open to exhaust warm air as cooler

air comes in from the evaporative cooler.

Evaporative coolers installed with upducts will need additional attic ventilation.

Filters remove most of the dust from

incoming air—an attractive option for

homeowners concerned about allergies. 

Filters can also reduce the tendency of

some coolers to pull water droplets from

the pads into the blades of the fan. Most

evaporative coolers do not have air filters

as original equipment, but they can be fitted to the cooler during or after installation.

Evaporative Cooler Maintenance

Save yourself a lot of work and money by

draining and cleaning your evaporative

cooler regularly. Build-up of sediment and

minerals should be regularly removed.

Coolers need a major cleaning every season, and may need routine maintenance

several times during the cooling season.

The more a cooler runs, the more maintenance it will need.

In hot climates where the cooler operates

much of the time, look at the pads, filters,

reservoir, and pump at least once a month.

Replace the pads at least twice during the

cooling season, or as often as once a

month during continuous operation. Some

paper and synthetic cooler pads can be

cleaned with soap and water or a weak

acid according to manufacturer’s instructions. Filters should be cleaned when the

pads are changed or cleaned. Caution: Be

sure to disconnect the electricity to the

unit before servicing it.

Two-Stage Evaporative coolers

Two-stage evaporative coolers are newer

and even more efficient. They use a 

pre-cooler, more effective pads, and more 

efficient motors. They don’t add as much

humidity to the home as single-stage

evaporative coolers, but are still much

more efficient than air conditioners.

Drawbacks of Evaporative Coolers

Evaporative coolers should not be used in

humid climates because they add humidity. Also, they cool your house down to a

higher temperature than an air conditioner would. They require maintenance

(albeit easy) about once a month. If the

cooler is installed on the roof, there is

some roof deterioration caused by routine

maintenance trips. A sunlit rooftop cooler

will be about 1 degree Fahrenheit less

effective than a shaded cooler. Rooftop

maintenance also requires using a ladder,

which may be an inconvenience.

Managing Your 

Home's Ventilation

Remember the following if you plan to

cool your home with ventilation:

• Learn how air flows naturally 

through your home.

• Take advantage of cool night air, 

and ventilate your home by natural 

or mechanical methods.

• Keep a clear path for airflow both 

inside and outside your windows.

• Close windows, doors, and window

coverings in the morning before your

home starts to heat up.

• Avoid producing heat in your 

home when it’s hot outside.

• Wear cool clothing.

• Raise your air-conditioning thermostat

to a more economical temperature. 

Turn it off completely if you’ll be 

gone for an extended period.
Resources 

The following are sources of additional information 

about fans and ventilation. The list is not exhaustive, 

nor does the mention of any resource constitute a 

recommendation or endorsement.

Ask an Energy Expert

DOE's Energy Efficiency and Renewable Energy 

Clearinghouse (EREC) 

P.O. Box 3048

Merrifield, VA 22116

Phone: 1-800-DOE-EREC (363-3732)

TDD: 1-800-273-2957

Fax: (703) 893-0400

E-mail: doe.erec@nciinc.com

Online submittal form:

www.eren.doe.gov/menus/energyex.html

Consumer Energy Information Web site:

www.eren.doe.gov/consumerinfo/

Energy experts at EREC provide free general and technical

information to the public on many topics and technologies

pertaining to energy efficiency and renewable energy. 

DOE’s Energy Efficiency and Renewable 

Energy Network (EREN) 

Web site: www.eren.doe.gov

A comprehensive online resource for DOE's energy 

efficiency and renewable energy information.

Consumer Reports

101 Truman Avenue

Yonkers, NY 10703

Web site: www.consumerreports.org

Good source of unbiased information about fans 

or other appliances.

DOE Office of Building Technology, State 

and Community Programs (BTS) 

Web site: www.eren.doe.gov/buildings/

In partnership with industry and government, develops,

promotes, and integrates energy technologies and practices

to make buildings more efficient and affordable. Here are

some other BTS web sites:

Building Energy Software Tools Directory

Web site: www.eren.doe.gov/buildings/tools_directory/

Describes many energy-related software tools, including

those for determining airflow and ventilation needs. 

Cooling Your Home Efficiently

Web site: http://www.eren.doe.gov/buildings/

heatcool_cooling.html 

Energy Star®

DOE and U.S. Environmental Protection Agency

Phone: (888) STAR-YES (782-7937)

E-mail: info@energystar.gov

Web site: www.energystar.gov 

Provides lists of energy-efficient products, including 

air conditioners. 

Home Energy Magazine

2124 Kittredge St., #95

Berkeley, CA 94704

Phone: (510) 524-5405

E-mail: contact@homeenergy.org

Web site: www.homeenergy.org

A source of information on reducing energy consumption

in the home. 

Fans—Sustainable Building Sourcebook

Green Building Program 

Web site:

www.greenbuilder.com/sourcebook/Fans.html

Heating and Cooling–Consumer Energy Center

California Energy Commission

Web site: www.consumerenergycenter.org/homeandwork/homes/inside/heatandcool/

Further Reading 

Ceilings and Attics: Install Insulation and Provide 

Ventilation, BTS, February 2000. Available in PDF at

www.eren.doe.gov/buildings/documents/pdfs/26450.

pdf and in print from EREC (see "Ask an Energy Expert"

above).

Cooling Your Home Naturally, EREC, October 1994. Available in PDF at www.eren.doe.gov/erec/factsheets/coolhome.pdf, in HTML at

www.eren.doe.gov/erec/factsheets/coolhome.html, and

in print from EREC (see "Ask an Energy Expert" above). 

Energy-Efficient Air Conditioning, EREC, June 1999. 

Available in PDF at www.eren.doe.gov/erec/factsheets/

aircond.pdf, in HTML at www.eren.doe.gov/erec/factsheets/aircond.html, and in print from EREC (see "Ask

an Energy Expert" above). 

Whole House Fan, BTS, March 1999. Available in PDF at

www.eren.doe.gov/buildings/documents/pdfs/26291.

pdf and in print from EREC (see "Ask an Energy Expert"

above). 

Installing and Maintaining Evaporative Coolers, Home

Energy Magazine Online, May/June 1996. 

Available in HTML at www.homeenergy.org/archive/

hem.dis.anl.gov/eehen/96/960511.html.

8