Do Window AC Units Bring In Outside Air?

If you live in a place that has air pollution or dirty air outside, then the air quality inside your home is a top concern.

Since window air conditioners go through the wall to the outside of your home, you might be wondering if they pull in air from the outside.

Window air conditioners do not bring in outside air. Instead, they recirculate the air that’s already inside your home, cooling and filtering it in the process. 

Window air conditioners stick outside of your home because they need to dump heat outside. Window ACs do not exchange air with the outside, they only exchange heat with the outside.

Do window AC units provide fresh air?

Window AC units do not provide fresh air to your home. However, window ACs have air filters in them. So window AC units provide filtered air to your home.

So if you’re concerned about a window AC bringing in outside air into your home, don’t worry—it doesn’t. However, if your window AC has a vent lever, then you can adjust the amount of fresh air that it brings into your home.

The main thing that all window ACs do (besides cool air) is provide air filtration as well. There is a distinct difference between fresh air and filtered air.

What’s the difference between fresh air and filtered air?

Fresh air is air from the outside of your home.

Filtered air is air that’s passed through a filter to remove particles.

Most window ACs filter the recirculated air that’s already inside your home, removing particles in the process.

However, an air filter cannot remove gaseous compounds such as carbon dioxide and carbon monoxide. The air filters in window ACs are also not very good at removing tiny microscopic particles such as smoke particles. So that’s why it’s sometimes necessary to get fresh air from the outside.

That being said, there are some models of window ACs that DO provide fresh air to your home. But these types of models are fairly rare.

If your window AC has a vent lever, then that’s how you can tell if it is capable of providing fresh air to your home.

What is the window AC vent lever used for?

The vent lever on a window AC is used to open the outside air vent. When the outside air vent is opened, fresh outside air is allowed to flow into your room.

So why would you want to bring in outside air into your home? There are a few reasons:

  • The air inside your home is stale, so you want to bring in some fresh air
  • The air inside your home is smoky or dirty
  • The air outside is cooler than the air inside your home, and you want to cool your home

The most common reason why you would want to bring in fresh air is so the air inside your home doesn’t get stale.

Stale air is basically air that’s no longer fresh. There isn’t really a technical definition of “stale air” but it can be thought of as air that has an unpleasant smell.

Musty smells alone are enough of a reason to want to bring in fresh air. But if your window AC is producing those bad smells, then you’ll want to take care of that by cleaning it out.

Another reason for bringing fresh air into your home is if your home’s air is smoky or dirty.

Smoky air is usually caused by cooking. Bringing in fresh air from the outside will displace the smoky air inside your home, eventually getting rid of it completely.

Dirty air inside your home can be caused by all sorts of things—dust, hair, and pets are some of the most common.

If the air outside your home is cooler than the air inside your home, then you can open up the window AC vent to get “free cooling” from the outside. This is usually only needed in the fall and springtime.

If you have a bunch of people in your home, it might get hot. So you can turn on your window AC in “fan-only” mode and open up the outside air vent lever to bring in fresh, cool air from the outside.

Do window ACs circulate air?

All window ACs do circulate air. This means that the air inside your home is recirculated through the air conditioner as the AC filters and cools the air.

The window AC circulation process goes like this:

  1. The window AC’s fan draws in air from the inside of the room
  2. The air passes through the air filter to remove particles
  3. The air passes through the evaporator (cooling) coil to cool the air
  4. The air is pushed out of the air register on the front of the AC, back inside the room

This whole process happens continuously, as long as the AC is running.

If the window AC is in Fan Mode or “Fan-Only” mode, then the cooling is turned off—the air from your room is only filtered when it circulates through the window AC.

What is Fan Mode on a window AC?

Fan Mode or Fan-Only mode is a setting on the window AC that runs the fan without providing any cooling. It’s basically like having a wall-mounted fan blowing air around your room.

So why would you want to use Fan Mode on a window AC? That kind of defeats the whole purpose of using an air conditioner right?

Actually, there are some scenarios when using fan-only mode on a window AC is useful.

For instance, if the outside air is cooler than the air inside your home, you can take advantage of this to get “free cooling” by opening the fresh air vent. When you open the fresh air vent and turn on fan-only mode, the fan in your window AC draws in the cool outside air into your home.

Another scenario of when you would use Fan Mode on your window AC is if you want to filter the air in your home. Window ACs have an air filter inside them that will capture most dust and hair particles. However, for smaller particles such as pet dander and smoke, you’ll need something with a stronger filter such as an air purifier.

Another reason why you would use Fan Mode on a window AC is if you just need the fan to run! Sometimes, it’s not hot enough to warrant turning the entire window AC on. There are some cases where it’s just a little warm, so you can get away with just turning the fan on.