Does a Window AC Take Air from Outside?

It’s a common belief that window ACs bring fresh air into your home from the outside. We’re here to tell you—that’s not true. Instead, a window air conditioner normally pulls air into it via a fan, cools and filters it, and then recirculates that air back into the building. For those who ask, “Does a window AC take air from outside?”, we’ll now provide a more detailed explanation of how it works.

How a Refrigerated Air Conditioner Works

An evaporative unit will pull outside air into a building. This air is first drawn through water-soaked pads to cool it. But that’s not what a refrigerated AC, the most common type, does. It blows air across a coil, through which refrigerant flows; the temperature of the air falls as it passes through the system. Heat is absorbed in the process.

A window AC features ventilation grates on the side. These may seem positioned to draw in outside air. However, they only allow air into the condenser coil to help cool the machine so it doesn’t overheat. Meanwhile, hot air is exhausted through the rear vents.

A Window AC Is a Sealed System

Window air conditioners are sealed, so therefore won’t pollute the air they cool. People may find that if there’s smoke pollution outside, it tends to get indoors. It’s not coming through the AC but rather through open windows, cracks in doors, or small openings in walls and even a unit that might need to be repaired or replaced.

If you find the AC filter becomes dirty more quickly, this same process may be in play. The filter captures particles from indoor air drawn into the unit, so it can recirculate clean air. Without a filter, or if the filter is clogged, particles can damage the unit. A clogged filter can also restrict airflow and cause the AC to strain and work harder to provide cool air.

The Same Goes for All Window ACs

Most window AC units are standalone box-shaped machines. These fit onto the window sill and are easy to install. The challenge is to create an effective seal around the unit, so air cannot get in or out through any gaps. Otherwise, the unit will work harder and you’ll have to pay for using more electricity.

Window ACs use only the air from your home to provide cooling. So do portable split system AC units. These have a tower-style AC unit and an exhaust hose that pushes out warm air via a window fitting. Newer models are often quieter, offer better filtration, and include smart controls.

Fresh vs. Filtered Air: When Does a Window AC Take Air from Outside?

The air you normally feel blowing from a window AC is filtered to remove any pollutants and particles. But the unit won’t remove carbon dioxide, carbon monoxide, and other gasses or microscopic particles that make up, for example, smoke. Fresh air differs from filtered air in that it originates outside your home.

You may be wondering why you’d want to let air in using a system designed to prevent that. That’s what the vent lever on your window AC is for. If the air in your home is stale, smoky, dirty, or smelly, bringing fresh air in can help clear out the pollution. Opening the vent can also provide efficient cooling if the air is cooler outside than inside.

So, yes, a window AC can take air from outside, but only if you want it to.

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