What Is a Window Fan?

The U.S. Department of Energy says window fans use little energy and can provide effective cooling in many climates.

What is a window fan?

A window fan is a fan that sits in an open window. Window fans blow air into or out of a home to cool and ventilate it. Depending on the model, window fans can come with a remote control, a thermostat, an auto-off timer, twin fans, and several speeds. Reversible window fans can be switched between intake and exhaust.

What Does a Window Fan Do?

Window fans cool a home by pulling in outdoor air when it is cooler than the air inside and pushing warm indoor air out. They move air. They do not cool it the way an air conditioner does.

Window fans use little energy, according to the U.S. Department of Energy. They are not a replacement for air conditioning in extreme heat. Ready.gov says not to rely on a fan as your primary cooling device.

Some window fans have a timer or a thermostat. The Lasko W09550, for example, has an 8-hour auto-off timer and a built-in thermostat that turns the fan on or off automatically.

On hot days, the Department of Energy advises closing all windows and exterior doors when outdoor temperatures are higher than indoor temperatures. Run the fan again when the air outside is cooler, which is usually at night.

A window fan set to exhaust can also help clear cooking smells and stale air. The EPA says operating window or attic fans, when the weather permits, increases the outdoor ventilation rate. Do not run a window fan when there is wildfire smoke outside. The EPA’s advice then is to keep windows and doors closed.

What Does a Window Fan Not Do?

Window fans do not work well in winter.

This is because they pull cold air inside your home while expelling warm air.

They also do not cool a home when the air outside is warmer than the air inside.

For example, if it is 90 degrees Fahrenheit outside and the window fan is set to blow inward, the fan will only bring hot air into the house. Fans also have limits in extreme heat. The CDC says to use fans only if indoor temperatures are less than 90°F, because above that a fan can increase body temperature. If your home stays hot, go somewhere with air conditioning.

How Do Window Fans Work?

Window fans work by drawing the air from either outside or inside your house.

If the fan is set to draw air in, pick a window on the cooler side of the home. The Department of Energy says windows near cooler, shaded outdoor areas provide the best intake air.

The Department of Energy says window fans are best used in windows facing away from the prevailing wind, exhausting hot air from the home. To cool as much of the home as possible, tightly close windows near the fan and open windows in rooms far from the fan.

A fan set to exhaust pushes hot air and smells out. Outdoor air then comes in through other open windows to replace it.

Types of Window Fans

Window fans come in a variety of sizes and types to fit most windows. They also come with a wide range of features to meet your every need.

Here are some of the most popular types of window fans:

• Horizontal window fan
• Vertical window fan
• Window fan with thermostat
• Window fan with remote
• Window fan with filter
• Dual window fan
• Box window fan
• Window fan for large window
• Window fan for small window
• Expandable window fan
• Reversible window fan
• Portable window fan

What Is a Horizontal Window Fan?

A horizontal window fan fits in standard-size windows or wider windows.

These fans are usually wider than they are tall to fill in all the gaps in the open window. Horizontal window fans are the most common type of window fan.

What Is a Vertical Window Fan?

A vertical window fan is one that stands upright in a tall, narrow opening, such as a slider window.

Check the manual before standing a fan on its side. Vornado says its Transom is designed for horizontal installation only, in windows that open up and down.

What Is a Window Fan With a Thermostat?

Some window fans come with thermostats.

A thermostat is a device that measures the temperature and turns a heating or cooling system on or off to maintain the desired temperature.

Window fans with thermostats turn on and off automatically to help regulate the temperature in your home.

What Is a Window Fan With a Remote?

Window fans with remotes allow you to control all the functions of the fan with one hand.

All you have to do is press a button on the remote and your window fan will turn on or off, change modes, or adjust speeds.

You won’t have to stand up or walk over to your window fan to make changes.

This is useful for anyone with limited mobility, or when the fan is in a window that is hard to reach.

Do Window Fans Filter the Air?

Most window fans do not filter the air. The Lasko, Vornado and Air King window fan pages checked for this article do not list a smoke or odor filter. A window fan pulls outdoor air in, so whatever is in that air comes in with it.

Do not use a window fan when the air outside is smoky. During wildfire smoke, the EPA says to keep windows and doors closed.

What Is a Dual Window Fan?

Dual window fans are window fans with two fans instead of one.

The two fans sit side by side in one housing. On some models each fan is controlled separately. Lasko says the independently controlled motors in its W09550 let you switch between intake, exhaust, or exchange mode.

On those models, one fan can be set to intake air and the other to remove air.

Dual window fans are also called twin window fans.

What Is a Box Window Fan?

The largest window fans are box-shaped whole house models. The Air King 9166F, for example, has a 20-inch blade and moves up to 3,560 CFM on high, according to Air King.

They need a wide opening. Air King lists a window 27 to 38 inches wide for the 9166F.

Read: What Is a Box Fan?

What Is a Large Window Fan?

Larger window fans have bigger blades and stronger motors, so they move more air. Air King lists its 20-inch 9166F at 3,560 CFM on high with a 1/6 HP motor, and its 16-inch 9155 at 2,470 CFM with a 1/16 HP motor.

Air King calls the 9166F a whole house window fan.

Air King says its window fans are also powerful enough for light commercial use.

What Is a Mini Window Fan?

Window fans that are made to fit in small windows have less power than those designed for larger windows.

For comparison, Lasko lists its twin 9-inch window fan, the W09550, at up to 560 CFM.

Smaller window fans will also have a narrower fan blade, which will cause them to draw less air into the home. Mini window fans are perfect for small apartments, condos, dorm rooms, and other small spaces.

What Is an Expandable Window Fan?

Expandable window fans have side panels that slide out to fill the gap between the fan and the window frame.

Each model fits a set range of widths. Lasko says the W09550’s expander panels fit most double hung windows from 24 to 32 inches wide. Vornado says its Transom fits windows from 26 to 40 inches wide. Measure the opening before buying.

Expandable window fans are perfect for people who move often or people with different-sized windows.

What Is a Reversible Window Fan?

Window fans that are reversible can be set to intake or exhaust air.

Some reverse at the press of a button. Vornado says its Transom electronically reverses to exhaust stale indoor air.

Reversible window fans are perfect for people who want to change the direction of the airflow in their homes.

You may want to do this when the seasons change, or during different times of the day.

What Is a Portable Window Fan?

A portable window fan is one that can be moved from window to window.

This type of fan is perfect for people who want to move the air around their home without having to buy several new window fans.

Small twin window fans such as the Lasko W09550, which Lasko lists at 8.0 lb, are light enough to move from room to room.

Where Do You Place a Window Fan?

You can place a window fan in any room in your house with a window.

Here are places where you can put a window fan:

• Living room
• Kitchen
• Bedroom
• Basement
• Attic
• Garage

Keep window fans away from water. Lasko’s W09550 manual says not to use the fan near water or wet locations such as a bath tub. In a multi-level house, the Department of Energy says the fan should be on the upper level, if possible, with open windows on a lower level.

Read: WhatIs an Attic Fan? (Explained for Beginners

Does a Window Fan Have To Be in a Window?

Yes, a window fan must be in a window to work effectively.

It does not have to be a ground-floor window. The window has to be a type and size the fan is made for. Vornado, for example, says not to install its Transom on crank, casement, or tilt and turn windows.

The fan needs an opening to the outside so it can take in or expel air. An open ground-floor window is also a security risk. Some fans let you close the window behind them. Air King says its Storm Guard feature lets the window be closed behind the fan during inclement weather or when securing the home.

What Are the Advantages of a Window Fan?

Window fans have many advantages over traditional air conditioners.

The Department of Energy says window fans use little energy and can provide effective cooling in many climates. Small twin models are also light and easy to move. They work in any room with a window the fan is made to fit.

However, a window fan can also have disadvantages over an air conditioner, which include:

• A fan only cools when the air outside is cooler than the air inside, and it should not be relied on in extreme heat
• Less powerful motors may not be able to cool down a whole house or room
• Depending on the layout of the home, several fans may be needed
• If you don’t use a screen along with a window fan, insects could get into your home

How Many Window Fans Do I Need?

One window fan is enough to start. Set it to exhaust and open a window in another room so air is pulled through the home. The Department of Energy says to close windows near the fan and open windows in rooms far from the fan.

With two fans, one can bring air in while the other pushes air out.

If you get a dual window fan or reversible window fan, one window fan can do both jobs.

The Department of Energy says that, depending on the layout of your home, you might want to use several window fans working together to pull air through the home.

One window fan may not be able to cool down a whole house.

Spread the fans out. The Department of Energy gives the example of fans in several upstairs bedrooms, which cool each bedroom and work together to pull air in through the rest of the home.

Here are some other helpful tips:

• In a multi-level house, put the fan upstairs and open windows downstairs
• If that is not practical, ventilate each level with its own fan
• Bigger window fans (that fit your windows) will create a stronger airflow

Window Fan Examples

Here are three window fans listed on their makers’ websites, with the makers’ own specs:

Window Fan Safety

• Extreme heat: the CDC says to use fans only if indoor temperatures are less than 90°F. Ready.gov says fans do not reduce body temperature or prevent heat-related illnesses.
• Smoke: do not run a window fan when there is wildfire smoke outside. The EPA says to keep windows and doors closed.
• Rain: check the manual. Lasko’s W09550 manual says not to use the fan near water or wet locations. If the manual does not say the fan can be used in rain, turn it off, unplug it and close the window.
• Cords: plug the fan straight into a wall outlet. Lasko’s manual says to avoid extension cords and power strips.
• Closing the window: Air King’s manual for the 9166 says not to close the windows while the fan is in operation.
• Children: Lasko’s 2138 window fan manual says never to leave children unattended when the fan is on or plugged in.

Final Thoughts: What Is a Window Fan?

Before buying a window fan, measure the window opening and compare it with the width range the maker lists. Then compare airflow in CFM and check the manual for the window types the fan is made for.

Now that you know what a window fan is, you may have some other related questions.

Read these articles about window fans:

• Is It Safe To Sleep With a Fan in the Window?
• Are Window Fans Safe in the Rain?
• Is It Better To Have a Window Fan Blowing In or Blowing Out?

Sources

U.S. Department of Energy (fans for cooling)
U.S. Department of Energy (ventilation systems for cooling)
CDC (heat and your health)
Ready.gov (extreme heat)
EPA (wildfires and indoor air quality)
EPA (improving indoor air quality)
Lasko (W09550 twin window fan)
Lasko (W09550 manual)
Lasko (2138 twin window fan manual)
Lasko (3733 box fan manual)
Vornado (Transom)
Air King (window fans)
Air King (9166 instructions)

Reviewed October 2026. We corrected the placement and how-many-fans advice to match the U.S. Department of Energy, replaced unsupported fan types, features and product picks with makers’ published specs, and added a safety section on heat, smoke, rain and cords, using the Department of Energy, the CDC, Ready.gov, the EPA, Lasko, Vornado and Air King.