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Can you use an air purifier with the windows open?

An open window can affect air purifier efficiency, but leaving a window open for small sessions works.
Updated on February 20, 2024
Written by
Michelle Honeyager
Michelle started writing for HouseFresh in 2023. She is passionate about home topics and has been published in top publications, including CNET, Bankrate, Remodeling Today, Atlanta House & Home and Remodeling Today Triangle.
An air purifier next to an open window

Can you crack open a window with your air purifier on? It can be a little confusing. Some manufacturers discourage you from opening windows during use, while others say up to 20 minutes at a time is fine. 

Generally, opening a window can reduce your air purifier’s efficiency. That’s because it’s now working to filter out pollutants and other particulates coming from outside. If you like the smell of fresh air, you can open a window for a bit, but keep it shut if you’re at risk of allergies or an asthma attack.     

Is it okay to open your windows? Should you keep them sealed tight? There’s a lot of conflicting advice online. For instance, opening your windows in humid regions may raise your home’s relative humidity too much and make it a breeding ground for mold. But during the COVID-19 pandemic, experts encouraged us to keep those windows open to improve air circulation and reduce the risk of respiratory infection. Then, there’s the added complication of having an air purifier running at home. Looking for some concrete answers? Read on to learn more about using an air purifier with open windows. 

What happens when you run an air purifier with the windows open?

There are a few things that happen when you run an air purifier with the windows open, such as:

  • Decreased air purifier efficiency. One study in the Building and Environment journal examined using an air purifier with an open window in a nursery environment. The air purifier had a particulate reduction rate of 63% with the window closed and a 46% particulate reduction rate with it open.   
  • More pollutants to filter. The study above also looked at the environment. One window was right next to a parking lot, increasing the indoor air pollution in the room when the windows were open. Another study in the Science of The Total Environment journal found that using an air purifier with closed windows kept additional outdoor pollutants at bay.   
  • Potential increase in health risk. If you’re using an air purifier to clean the air of allergens or asthma triggers, opening the window could invite these health hazards in. The EPA encourages to keep windows closed if it poses a health risk to people with asthma. 

If you don’t want to risk opening the windows at all, here are some tips for ventilating without windows.

What’s the advice from air purifier manufacturers?

Advice from air purifier manufacturers varies. Some say you can open a window for a limited time or just one window at a time. Others have a hard no-open-window stance. Below are some nuggets of advice from major brand manufacturers.  

“The windows have to be closed when the purifier is in use. This way, outdoor pollutants won’t affect the effectiveness of the purifier and in turn, increases the HEPA’s lifespan. For ventilation, the windows can be opened for 15-20 minutes so that the air in the house will be changed once. After closing the doors and windows, the air quality will quickly return to the safe range when the purifier is in use.”

“While our purifiers work best in rooms with closed windows, we never want to discourage you from opening your windows for a short time to get some fresh air! However, it is important to keep in mind that if outside air has a high level of pollutants, it may hamper the ability of the purifier to reduce the ambient level of particulates and gases in your space.”
“Operate your Mila in an enclosed area. Close all doors, windows, and other openings connecting to the outside of the room.”
“Even if an air cleaner is present in a room, it is important to ventilate. This increases the amount of oxygen in a room, but when too much air enters from outside, the Air Purifier may have trouble removing all impurities. Our tip is, therefore, to keep one open window or door at a time so that the air purifier can maintain its airflow.”
“Your air purifier works most efficiently in a sealed environment – opening the windows can allow more pollutants to enter the air in your home, which means your machine will take longer to work.”

The do’s and don’ts of running an air purifier with the windows open

Sometimes, it can be necessary to air out your home and get some fresh air in there, especially if you believe there are pollutants present. If you need a (literal) breath of fresh air, below are some tips for having the windows open while the air purifier is running. 

What you should do

Have the window open for a very short time. If you really feel you need ventilation, keep the window open for no longer than 20 minutes.
Limit open windows. If you do open windows, have only one window open at a time to avoid overwhelming the air purifier.

What you should avoid

Never open the window if you suspect air pollutants or other poor air conditions. For instance, if you live near traffic or there is smoke in the air, keep the window closed. Keep windows closed during high humidity, as that can create a mold risk
Don’t open the window if it might trigger allergies or asthma. It might be tempting to think you can get the best of both worlds: fresh air and clear air, as long as you have the air purifier by the window. But the air purifier might not keep up with allergens or asthma triggers, especially during high allergy risk days. 

In general, a little bit of common sense goes a long way. Don’t open the window too much, if at all, and avoid opening the window during bad air conditions.  

Wrapping up

You might feel confused because general advice about whether you can open a window while running an air purifier varies. To put it simply, opening a window can reduce the efficiency of the air purifier, as it may now be working against incoming outdoor pollutants. If you do want to open a window, have only one open for no longer than 20 minutes. Never open a window if it might cause issues for someone with allergies or asthma or if air quality is bad.       

About the author

Michelle Honeyager

Michelle started writing for HouseFresh in 2023. She is passionate about home topics and has been published in top publications, including CNET, Bankrate, Remodeling Today, Atlanta House & Home and Remodeling Today Triangle.