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Is It Bad to Leave My Windows Open When the AC is On?

Air conditioning units use up a fair amount of energy to keep your house cool, so some people opt to open their windows to get extra cool air during the summer months. But were you aware that keeping your windows open while the air conditioning is running can often counteract the functions of your AC unit?

Here's the complete rundown on what you need to know about leaving your windows open with the AC on:

How Air Conditioning Works

Your AC unit runs by sucking all the heat and humidity from the air in your home and sending it outside so that it can push out cool and clean air back into the house. This means that it requires a closed system to work optimally. Air conditioners work best when windows are closed so that the unit can deal with the air in the house.

Keeping the Window Open Gives your AC More Work

Since your AC unit works best in a closed system, opening your window gives your AC more work to do. By opening the window to get a cool breeze, you are letting in the humidity your unit aims to eliminate. You're also wasting all that air that your AC has worked hard to make cool by letting it flow out the window!

When you keep your windows open, your air conditioning unit will have to be kept on longer to work against filtering the heat from the new air. This gives it little rest and places a high strain on the AC unit. Not only will this build up your energy costs, but it can also lead to premature breakdowns and a shorter lifespan of your AC unit.

It’s not just the humidity that's an issue for open windows too. Outside air can potentially be dirty, and your air conditioning unit is not suited to filtering out any harmful particles from outside.

This means that polluted air will recirculate in your house, which can cause potential health concerns for anyone in the house. In addition, since your AC unit isn't fit to deal with the dust from outside air, this can also harm the system by clogging up the filters and coils. This will make your AC run much less effective and increase its chances of breaking down!


While leaving your windows open when the AC is on may seem harmless, it can be detrimental to you and your home.

Since your air conditioning works by pushing out cool air and filtering heat and humidity from existing air, opening your windows gives the unit extra work to deal with the air coming from outside.

Not only does this waste energy from the AC, but it also means you are letting filtered cool air escape. The air from outside can also be dirty and affect your health and the longevity of your air conditioning unit.

If you want to save energy and keep your house's air cool and clean, keep your windows closed when the AC is on!

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