Air Purifiers CANNOT Work Optimally If Windows are Kept Open

Josh Mitchell

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

Last Updated On

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Key Takeaways

  • No, you should not leave your windows open when using an air purifier. They work best when the room is completely closed off. 
  • Leaving windows open will make the air purifier work harder. This will demand more regular maintenance and will increase the time it takes to clean the air.
  • There are certain special scenarios when you may leave the window open such as when dealing with dangerous VOCs like formaldehyde. 

For the longest time, I was sabotaging the air quality in my house without realizing it. If you own an air purifier and crack open a window while it’s running, you may be doing the same thing.

I thought leaving a window open while using an air purifier helped improve ventilation and indoor air quality. However, the reality is that an open window makes life a little tougher for your air purifier and significantly reduces the effectiveness of your air purifier.

So before you crack a window with your purifier running, let’s explore why it’s important to keep it shut while using your air cleaner.

Do Air Purifiers Work With Windows Open?

Your air purifier will still work with the windows open. However, it will have to work much harder, and it’s not going to produce optimal results.

When I first got my purifier I didn’t completely understand how they work. So, I thought bringing fresh air into the home would help the purifier cleanse the air.

It doesn’t quite work that way. Air purifiers continually cycle the air in a room, filtering out pollutants and allergens. When you open a window, you’re interrupting this process, exposing your air to outdoor particles.

The outside air that comes in isn’t so fresh, and it has to be purified as well.

As soon as a window is opened, your air purifier will have to start the purification process all over again, wasting time and energy. While it will still work to purify the air, it will have to work much harder and it will be much less efficient.

So don’t be like me. Before you open a window, ask yourself if it’s worth sacrificing the air purifier’s efficiency and potentially exposing yourself to more pollutants.

When Do Air Purifiers Work Better: Closed Or Open Windows?

Air purifiers work better when your windows are closed. This should be obvious by now, but it’s worth stressing the point. An air purifier is at its best when windows are closed because the dirty outdoor stays outside. Your cleaned air will not be polluted by outdoor air with closed windows.

I love having my windows open, especially in the spring. I’ll occasionally open them up when the purifier isn’t running to help ventilate the room and reduce some indoor contaminants (and so I can listen to the birds and enjoy the breeze).

And, even if a window is open, your air purifier can still minimize airborne particulates in the room, which is better than nothing. I don’t know about you, but sometimes I’m willing to sacrifice a little indoor air quality so I can have my windows open!

Considerations When Opening Your Window While Using The Air Purifier

Since I love having my windows open, I completely understand that it’s not always practical to keep your windows closed all the time (like the time I burnt salmon filets on the stove). So, if you need to open your windows while your purifier is running, there are some essential factors to consider:

Outside Environment

I’m lucky I live outside of the city with very little outdoor pollution. However, if you live in a polluted area with a lot of car exhaust, wildfire smoke, or the like, do your best to avoid opening your windows while your air purifier is on.

When pollen counts are high in the spring, for example, I do my best to keep the windows closed so my air purifier works more effectively.

The Effect On Your Air Purifier

Air purifiers operate best in smaller, enclosed spaces with minimal disruptions. Repeatedly filtering the same air reduces the number of pollutants in the air and the particles trapped decrease with each filtration cycle, resulting in cleaner air.

Opening your windows forces your air purifier to filter additional outdoor air, decreasing the effectiveness of the purifier and the lifespan of the filter. Limiting the amount of air an air purifier has to clean can significantly increase its efficiency and prolong the filter’s lifespan.

Energy Costs

The one thing that gets me to keep the windows closed more than anything else is the energy cost of leaving them open. Opening your window lets fresh air escape and unclean outside air in.

To compensate, you’ll have to increase the fan’s speed or run your air purifier longer. Using the cleaner more frequently and at higher speeds often results in higher energy costs.


With the windows closed, the air purifier only takes a few hours to significantly enhance indoor air. For people with severe respiratory conditions or households with cigarette smoke and pets, the less time it takes to cleanse the air, the better. Keeping the window closed while the air purifier runs can significantly decrease the amount of time it takes to clean the air.

Rain Or Wind

Keep your windows closed during rainy or windy weather. When the wind is blowing and the rain is pouring, more air can be blown into the room, compromising the effectiveness of your air purifier.

When Should You Use An Air Purifier And Open Windows?

You generally should not open the windows when your air purifier is running. However, there are some scenarios where it may be beneficial. Whether or not you can open your window or need to leave it closed while running your air purifier depends on your indoor pollutants and air filter.

For example, if you’re cleaning out chemical fumes from painting or cleaning, opening a window can help ventilate the room and improve your air. Similarly, if you’re using an air purifier with a HEPA filter, which captures fine particles like pollen and dust, opening a window during peak pollen season can help reduce the allergen load in the room.

But it’s always about balance. Leaving your windows open too long can backfire and let too much pollen into your room. I usually just leave mine closed, but it’s not the end of the world if you want to open yours for a bit.

In general, though, it’s best to keep windows closed when using an air purifier so it doesn’t become overloaded with outdoor pollutants and allergens. Consider your specific air purifier’s capabilities and the indoor pollutants you’re dealing with before you open the window.

What Is The Correct Setting Of An Air Purifier If Windows Are Open?

If you need to use an air purifier with your windows open, it’s best to set it to its highest fan speed to ensure maximum air circulation in the room. Remember, the air purifier will need to work harder to filter outdoor pollutants and allergens that enter through the window.

How long should an air purifier run with open windows?

There is no specific time designated for how long you can leave your windows open when using an air purifier. In general, it may take only a few hours for an air purifier to cleanse the air in a room. However, with the windows open, it will take much longer due to the constant influx of outdoor air.

People Also Ask (FAQs)

Do air purifiers work around corners?

Air purifiers can work around corners, depending on their design and airflow capacity. However, their effectiveness will be reduced if obstacles obstruct the air flow.

Is it better to put the air purifier upstairs or downstairs?

Whether you should put your air purifier upstairs or downstairs depends on the layout of your home and the areas where you spend most of your time. Put your air purifier in the room where you spend the most time or the room that has the most pollutants.

Are plants as good as air purifiers in cleaning the air?

Plants are not as good as air purifiers at cleaning the air. While plants can help remove some pollutants from the air, their air purification capabilities are not as good as air purifiers.

How can I monitor air quality in the home?

One way to monitor air quality in your home is to use an air quality monitor. These devices can detect pollutants such as particulate matter, VOCs, and carbon monoxide in real-time and provide information on your home’s air.


I’m always tempted to crack a window for some fresh air, and honestly, I probably open my windows more than I should when the purifier is on. If you’re tempted to do the same, just know that running your purifier with the windows open will compromise its effectiveness.

When your windows are open and your purifier is on, set it to its highest fan speed and monitor the air quality in your home with an air quality monitor. Enjoy the fresh air for a bit, and then close the windows so your purifier can do its job effectively.

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Josh Mitchell


Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

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Midea U Shaped Window Air Conditioner

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