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Do Air Conditioners Take in Air From Outside?


Air conditioners are one of our most trusted companions once the hot summer months arrive; they keep our indoor spaces cold and comfortable. They continuously introduce fresh air and remove the heat from your house. 

But have you ever wondered where the air coming out of the air conditioner is from? Do air conditioners pull in fresh air from outside the house, or do they recycle the same air within your living space? 

In this article, we’ll explore air conditioning mechanics and whether these devices take in air from the great outdoors.

How Do Air Conditioners Work and Bring Fresh Air?

Do air conditioners bring in air from outside?

Air conditioners transfer heat and recycle it into cooled air. The heat could be from existing indoor air or warm air from outside. This process relies on the refrigeration cycle, a fundamental thermodynamic principle. Once done, the cycled air passes through an air filter to remove pollutants and other contaminants.

The refrigeration cycle has four stages and circulates throughout these components: the compressor, condenser, expansion valve, and evaporator. 

The compressor, or an air conditioner pump, uses a special fluid called “refrigerant” to help the warm air flow into the condenser coils. The refrigerant flows in and expands, transferring heat into the coils. Using the refrigerant, the air changes from gas to liquid and vice versa, making it easier to conduct heat exchange.  

After receiving gas from the heat pump, the refrigerant releases heat, condensing it into a high-pressure liquid. After passing through a narrow valve or return ducts, the refrigerant rapidly lowers pressure, causing it to evaporate and become a low-pressure vapor. 

As this vapor passes through the indoor evaporator coils, it absorbs warmth from the air inside and circulates into cooling coils. Then, the evaporator coil blows air that’s cooled. The absorbed heat is eventually released outside through the condenser coils.

The released air then passes through air filters to trap pollutants that trigger allergies. An air filter is needed to ensure your family’s health is not compromised.

While most air conditioners bring cool air using existing air within the room, some air conditioners incorporate an “outside air” mode for fresh air intake. Regardless, the primary cooling mechanism remains the refrigerant and its cycle.

This cycle ensures efficient heat transfer and maintains a comfortable indoor climate by continuously absorbing indoor heat and dissipating it outdoors.

Where Does the Air Conditioner Pull Air From?

ACs can bring in fresh air from different sources depending on their design and system type. Here are the types of AC systems:

Central Air Conditioning Systems

A central AC unit is typically located outside the building. It consists of a condenser unit and an evaporator coil. These systems circulate refrigerant between the indoor and outdoor units to transfer heat and cool the air. 

Central air conditioners do not directly pull in air from the outside for cooling purposes. Instead, they recirculate and cool the air by removing heat. Such ventilation system is commonly found in residential units and small spaces. 

Window Air Conditioners and Split System

Window and split air conditioners are common in individual rooms or small spaces. In this case, the air conditioner pulls air from the room and cools it through refrigeration. 

A window AC is affixed to windows and includes a gauge that assists in regulating the volume of air coming in. A split AC has an indoor and outdoor unit that helps eliminate the unwanted heat inside your house, so it can keep cooling your place effectively. 

These two units do not bring in outside air for cooling; they work by recirculating and cooling the air inside.

Portable Units

A portable AC unit does use outside air to some extent but in a different way than other systems. Portable air conditioners pull in a warm breeze from inside, cool it through refrigeration, and then expel the heat outside through an exhaust hose.

The exhaust hose is one of the important components of a portable air conditioner. It is typically installed in a window or another opening in the room. This hose serves two purposes:

  • Exhausting Hot Breeze: The primary function of the exhaust hose is to expel the hot air generated during the cooling process to the outside. This helps maintain a temperature difference between the indoor and outdoor environments, allowing the air conditioner to continue cooling the air effectively.
  • Intake of Outdoor Breeze: As the hot air is expelled through the exhaust hose, a negative pressure can be created in the room. Outdoor air might be drawn into the room through gaps around windows and doors to balance pressure and maintain proper air circulation. This can lead to a slight air exchange between indoor and outdoor environments, but it’s not the primary cooling method.

It’s important to note that portable air conditioners are less efficient than other AC systems, such as mini splits or central ACs. They are more suitable for smaller spaces and temporary cooling solutions. While they use a small amount of fresh air from outside for pressure balancing, their primary cooling mechanism is recirculating and cooling the air within the room.

Traditional air conditioners, whether central or window/split units, do not primarily pull air from the outside for cooling purposes. They operate by recirculating and cooling the air within the building. While portable ACs use fresh air from outside to aid pressure balancing, they do not use outside air for cooling.  

Does an Air Conditioner Pull Air From Outside?

In most cases, no. Standard residential air conditioners do not pull air directly from the outside for cooling. Instead, they primarily recirculate and cool the air within their cooling space. This recirculation process is more efficient and effective for maintaining comfortable indoor temperatures and humidity levels.

However, there are certain situations and types of air conditioning systems where outside air can be introduced for specific purposes:

Fresh Air Intake

Some larger commercial or industrial HVAC systems include a “fresh air intake.” This allows a controlled amount of outdoor air to be mixed with the recirculated air for better air quality. 

In this scenario, air conditioners bring in fresh air from the outside. This outside air is usually filtered, conditioned, and adjusted to match the desired indoor temperature and humidity levels.

Cooling Towers

In certain industrial cooling applications, such as cooling towers, air may be drawn from the outside to facilitate the cooling process. These systems are used in large-scale industrial settings rather than residential spaces.

Ventilation Systems

Some homes and buildings have separate ventilation systems that bring outside air for improved air exchange and indoor quality. These systems are distinct from standard air conditioners and are designed to ensure proper ventilation rather than direct cooling.

It’s important to understand that most residential air conditioners are designed to recirculate existing air within the room due to energy efficiency, humidity control, and overall system performance. The misconception that air conditioners directly pull in air from the outside might arise from the general understanding of how an AC unit works or specific industrial cooling processes.

Why Do Air Conditioners Need Outside Air?

Typically, air conditioners bring in fresh air by using the existing air in the house. Although, there are certain situations and types of air conditioning systems where outside air can be beneficial. Here are some reasons why air conditioners might incorporate outside air:

Improved Indoor Air Quality

Introducing a controlled amount of outside air can help improve indoor air quality by diluting indoor pollutants and odors. This is particularly important in buildings with limited ventilation or spaces where better indoor air quality is needed.


Buildings require a certain amount of fresh air for occupants’ health and comfort. Inadequate ventilation can lead to stuffiness and the accumulation of indoor pollutants. 

Introducing an outside breeze through an air conditioning system can help bring additional ventilation and maintain a healthier indoor environment.

Humidity Control

In certain climates, introducing outside air can help with humidity control. Outdoor air is often drier than indoor air, and mixing them together can help lower indoor humidity levels, especially during humid conditions.

Energy Saving

In temperate climates, using outside air for cooling during cooler parts of the day or year (such as nights) can reduce the need for mechanical cooling. This approach, known as “free cooling,” can lead to energy savings by utilizing naturally cooler outdoor air.

Fresh Air Exchange

Some commercial buildings, such as offices and restaurants, benefit from a regular exchange of indoor air with fresh outside air. This helps maintain a comfortable and pleasant environment for occupants.

Exhaust and Makeup Air

In specific industrial and commercial settings, where exhaust systems are used to remove pollutants, introducing outside air as makeup air can help maintain pressure balance within the building and prevent negative pressure conditions. 

It’s important to note that these scenarios usually apply to larger commercial or industrial HVAC systems designed for specific purposes like ventilation, air quality improvement, or energy efficiency. On the other hand, residential air conditioners primarily focus on cooling the air efficiently without necessarily drawing in outside air.

Final Thoughts

Most residential air conditioners do not take in air from outside. Instead, they recirculate the air in your home or office space. This approach ensures better cooling efficiency, humidity control, energy conservation, and improved air quality. 

While some commercial systems may incorporate fresh air intake for enhanced indoor quality, the core principle remains the same: air conditioning systems primarily work by cooling and recirculating the air that’s already present indoors. So, the next time you enjoy the refreshing cold air, you’ll know that you’re feeling primarily the air you’ve been breathing all along.

If you’re interested in getting an AC, consult an HVAC professional or any trusted air conditioning company to ensure that it’s safe for your home’s age and that the system works effectively to comply with your cooling needs. 

JP Reyes

JP has been in the aircon industry for almost as long as he has been alive. As a child JP would help his tatay fix aircon units at their junk shop in Cavite. After graduating UP in the early 2000's, JP then started his own Aircon servicing business and within 5 years had 10 shops in 8 different cities. Fast forward to today and JP brings all his experience and expertise online to give readers trustworthy advice and reviews about Air-conditioning buying, servicing, cleaning and repair in the Philippines.

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