does window ac bring in fresh air

Does a Window AC Use Outside Air? (It’s Not What It Seems)

Window air conditioners do pull air in from the outside but it is probably not how it seems. 

The idea that the cool air you feel comes from a Window AC comes from outdoors is not true. At least in the case of refrigerated air.

But window air conditioners do utilize outdoor air in other ways.

Window air conditioners use fresh outdoor air in 3 different ways.

1. Fan mode
2. Ventilation
3. Evaporative

1. Fan mode allows you to to use your AC as a fan by opening a small ( very small) opening to allow fresh air in through your AC. Some AC s give you the ability to mix the outdoor air by opening the fan vent.

2. Ventilation. The ventilation grates on the side of the unit are deceiving because they might give you the idea that air is being drawn into the unit to be cooled and released into the room or house. But the ventilation grates are actually to pull air into the condenser coil department to help cool the machine and keep it from overheating.

3. Evaporative window units do

pull outside air into a room. The entire action of an evaporative window cooler is to pull outside air through water soaked pads into an area for cooling.

There are two distinctively different styles of window air conditioners. Refrigerated air and evaporated air.

Both are designed to sit in your window and blow cool air into your room. Only one blows air in from the outside of the house and the other conditions air from inside of the house.

Refrigerated window air conditioners are the more popular of the two types .

 At least in recent years. Evaporative window air conditioners used to be the main technology or method for cooling the house.

There was a big industry surrounding evaporative air coolers and all of the supplies you needed to mount a evaporative air conditioner on the outside of your windows and house. But those types of air conditioners have now taken a back seat.

Refrigerated air is the status quo in this generation.

What’s the difference in evaporative and refrigerated window air conditioners

Refrigerated air is cooled by blowing air over coils that have refrigerant flowing through them.
Evaporated air is cooled by blowing air over water.

Do refrigerated window air conditioners bring in fresh air from outside?

No. Refrigerated window air conditioners recirculate the air already in the room.

The design of a window air conditioner makes it easy to assume that air is being pulled into the unit from the outside due to the ventilation grates located on the sides and top of a ac window unit.

But those grates are now there to pull air into the refrigeration process. They are there to pull air into the back of the unit to help ventilate the condenser coils.

The cool air you feel from a window air conditioner is room air that is pulled in through the face of the unit and is circulated over the refrigeration coils. Then it is blown back into the room through vents at the upper point of the face of the ac.

A refrigerated window air conditioner sits in a window entirely to exhaust hot air through the rear of the unit outside.

But evaporative window air conditioners do get their supply air from the outside of the window.

The basic premise of a window evaporative cooler is to pull outside air over absorption pads that have been soaked in water and blow the water cooled air into the room.

Evaporative window air conditioners have a few different names that you may recognize them by.

The most popular is “swamp cooler” but recently they are more likely to be called “vent less air conditioners” or “exhaust free air conditioners

They are called vent less air conditioners because they do not require a way to vent hot air coming from the rear of the unit.

The simplest way to explain an evaporative cooler is to call it a fan that blows air through a stream of water.

In the case of window evaporative coolers, they require a direct hookup of water that continuously soaks pads that are inside the perimeter of the air conditioner.

And though they do not require any way to exhaust them, they do require a source of water that is either connected directly or added manually.

Certain “Portable air conditioners” are usually the ones that carry the moniker “ventless air conditioner” or “exhaust free”.

Whenever you find an air conditioner that says it does not need exhaust or is ventless, you know that you are looking at an air conditioner that needs a supply of water.

In other words you’re going to have to fill it with water on a regular basis.

Swamp Cooler Warning


And any appliance that has to be filled with water or extracts water like a dehumidifier will have to be cleaned regularly to avoid the production of mold and bacteria in the machine.

Legionnaires’ disease originated from poorly or never maintained evaporative air coolers that were allowed to have standing water in large commercial buildings. The bacteria was allowed to grow unchecked and then have access to the airstream through the air conditioning vent system.

A good reminder when you are dealing with any type of machine that affects humidity.


The other type of portable air conditioner is the one that does require a way to vent it.


And even though it is portable and can be placed throughout a room, it still has a large hose that has to be strung across the room to a window in order to expel the hot air created in the refrigeration process.


Portable but not exactly convenient.

There are some pretty clever ways to convert a window air conditioner into a portable air conditioner but the same problem exists of being able to find a place and a way to exhaust it.

Regardless, some areas just do not lend themselves too easy window access or water access for that matter.

So the terms “portable” and “convenient” are not exactly interchangeable when it comes to air conditioning.

Pros and cons of refrigerated window air conditioners.


Colder air.

Less maintenance. Refrigerated window air conditioners have a small filter that needs to be blown clean from time to time. And a complete cleaning only necessary on a yearly basis.

Do not need any source of water.

Extracts humidity

Easy to cover for the winter months.


Exhaust hot air from the rear.


Pros and cons of an evaporative window air conditioner.


Does not exhaust hot air from the rear.


Not as cool.

Adds humidity. The fact that they are nicknamed “swamp cooler” gives you the idea of what type of air quality you can get from an evaporative window air conditioner.

Needs a constant source of water. Either by directly hooking it up to a water faucet or hose connection or by filling it manually.

Requires much more regular maintenance to ensure that it doesn’t have issues with mold and bacteria.

Must be emptied of water when not in use.

It is easy to see that refrigerated window air conditioners are a much better choice if you have a convenient window to put it in.

If you do not have a convenient window, then choosing a vent less evaporative portable air conditioner is probably an easier solution than a refrigerated portable air conditioner.

But that is also determined by your access to a window or access to an attic.


There are two choices when it comes to window air conditioners.

1. Refrigerated
2. Evaporative

Refrigerated window ac units recirculate room air over cooling coils and returns the air as cool or cold.

Evaporative window units pull outside air through absorption pads that are continuously soaked in water.

Refrigerated air is more convenient and doesn’t require a source of water regardless if it be directly hooked up or a unit that you manually fill.

Evaporative window ac units have long been renamed” swamp coolers” because of the amount of humidity they add to a room.

But portable vent less air conditioners that use evaporative air are a welcomed solution when you have a area that needs cooling but you do not have window access to vent a refrigerated ac unit whether it be a fixed window unit or a portable that has to be vented with hoses.

Published by

Dennis Reed

Dennis Reed Owner and Author @