Do Window Air Conditioners Pull Air From Outside?

Window unit air conditioners are a godsend during the summer months when you want to prevent the air inside from becoming as hot and sticky as the air outside. Although they provide relief, you may be concerned about where that cool air comes from. It’s nice to relieve the heat, but not when it comes with a price to your health and safety. 

Though there are concerns that window air conditioners use outside air, this is only the case in some modes. The most popular type of unit filters, refrigerates, and recirculates the air already in your home. Some window air conditioners give you the option to allow outside air into your home, but these modes are often optional and can be turned off when the outside air is polluted. 

Your window air conditioner will likely not pollute your home with outside air. However, knowing the different types of window units, their settings, and how they can affect the air inside your home is crucial. To help you make the best decision for your home, refer to the information below to make your experience with your window unit safe and efficient.

How Window Air Conditioners Work

A window air conditioner works by using the hot air inside your home. The air from the room filters into the air conditioner and a coil full of refrigerant is compressed simultaneously. The air circulates around the cooling coil and back into the room, so the air goes in hot and comes out cold. 

Window Air ConditionersSystem
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There is a part of the window air conditioner that hangs outside of the window. This is where the vents from the air conditioner let out the trapped excess heat from the inside, leaving cool air in the house instead.

Instead of bringing in air from the outside, the unit recirculates the air you already breathe and makes it healthier through filtration. This recirculated air is cooler than the stagnant air inside a house without air conditioning. 

Types of Window A.C. Units

There are two main types of window A.C. units: standalone and portable. 

Standalone Units

This unit is the most recognizable window air conditioner, which sits on the windowsill itself. They are usually boxy and house a control panel on the unit. 

It is box-shaped and relatively easy to move, though, to work, it needs to be sealed into the window. This can cause concern if your windows are older and not as easily sealed. 

Standalone Units Air Conditioner
Standalone Units

This style of window unit is also relatively heavy and can only be efficient if proper sealing is possible. However, it is a cheap alternative when central air is not possible, and it can be very efficient in saving electricity if it is adequately sealed into the window. 

Portable Systems

Portable window units are a newer answer to the boxy traditional unit. They are composed of two parts: a tower-like unit that serves as the actual conditioner and a hose that connects to a window to let out the warm air. 

Potable Units Airconditioner
Potable Units

Generally, the conditioner sits on wheels, making it easy to move out of the way if needed. These portable air conditioners are often more expensive than a traditional window unit but are often more efficient and modern. Some advantages to a portable system include a smart system that is easier to control, quieter running, and better filtration. 

The Recirculation and Filtration System

The air that your window air conditioner puts into your home is, in most cases, not outdoor fresh air. However, it is fresh air because these air conditioners filter the air inside your home while they cool it, making it healthier to breathe. 

Both portable and standalone air conditioners use filtration and recirculation to cool your home. As previously mentioned, the hot air from your home is sucked into the air conditioner and put back into the house as cool air. This is called recirculation.

Recirculation works with the refrigerated compressor in your window unit, as it pushes the hot air around the coil and then pushes that air back out once it is cooled down. 

Recirculation  System

Another part that is integral to this system is the filtration system. Most air conditioners will come with Minimum Efficiency Reporting Value filters. These only filter large particles from the air in your home as it moves through the unit. These filters will catch most dust and pet dander in your home. 

If you are concerned with other allergens and smaller particles in the air, you can buy a High-Efficiency Particulate filter, which will take care of even the smallest particles that float through your home. 

The filtration system must be kept up for your air conditioner to work correctly. This means replacing the filter or cleaning it whenever it gets dirty. This will help the recirculation system run smoothly and keep you breathing clean, cool air. 

Do Window Air Conditioners Bring In Outside Air?

Window air conditioners, in most cases, do not bring in outside air. This is because the recirculation and filtration systems within the air conditioners work with the air already in your home. 

The idea that these units bring in outside air is logical because part of them hangs out of the window, but this part of the air conditioner merely vents the hot air from your house to make room for the cool air it will recirculate. 

In rare cases, window air conditioner units will bring in outside air. This is often because of the various settings on the air conditioner, which can be switched off. 

This can be a concern when the air outside of the home is polluted or dangerous, such as in the case of wildfires. Most air conditioners allow you to simply switch to recirculating the air inside your house if this becomes a problem. 

The “Fresh Air” Option

There are some cases in which your window unit may be able to bring in outside air. One of these is with the “Fresh Air” mode many air conditioners have.

This mode essentially opens the vent on the back of your unit to the outside, allowing air from outside the home through your air conditioner. 

There are a few reasons you might want to allow outdoor air into your home, including the air in your home being stale or odorous, the air in your home being smoky or dirty, or the air outside of your home being cooler than the air inside your home. 

If you do not wish to have outdoor air in your home, switch off the “Fresh Air” mode. If your air conditioner can use outdoor air, it will also have the option to switch it off. 

Other Considerations

There are a few additional considerations to keep in mind when it comes to window A.C. units. 

Other Window A.C. Modes

There are other instances in which outside air may be brought into your home through your window unit. This is usually because of the mode it is switched to.

For example, if your window unit switches to fan mode with the vent to the outside open, you will let air in from the outside due to the fan pulling it from the open vent. 

The fan mode works much like a regular fan. It does not cool the air, but it does provide a breeze and does circulate the air in the room, providing relief if the air is hot inside the home. 

Fan Mode On


Window air conditioning units can provide relief from a hot summer day. However, they only sometimes rely on the air from the outside to work. Both standalone and portable window units use the air inside of the home, filtering, cooling, and recirculating it to provide cold, clean air for you to breathe. 

It is essential to consider that you may want fresh air; in that case, you can use the fan mode or “Fresh Air” mode. However, in most cases, rest assured that your window unit is using the air inside your home, cleaning it, and making it more comfortable and healthy for you to breathe. 

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