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Do Air Purifiers Work With Windows Open (How About Doors?)

Here's a pro tip: Do not run an air purifier with the windows open. A common mistake that many people seem to neglect. We will explain why it is crucial to keep the windows closed when running an air purifier through scientific data. We will also address other related questions that we have received from time to time. We guarantee your air cleaner performance will be significantly boosted if you have not done so. Let's get started.
Short answer
Close windows when using an air purifier.

 

Can I Use An Air Purifier With A Open Window?

You should close the windows and door when using an air purifier to maximize the air cleaning effectiveness. It will prevent outdoor pollution like smog, CO, CO2, dust, pollen from entering the room and clean air from escaping. When you leave the windows open, it is impossible to achieve a healthy air status with persistent airborne pollutants coming in from outside. The air-cleaning process would be constantly interrupted, and the air purifier will have to restart the air purification again. It forces the air purifier to work nonstop resulting in a higher electricity bill and shorter filter life. The bigger the opening window, the less effective an air cleaner is.

Should You Run An Air Purifier With Windows Open?

An air purifier will work with the windows open, but the air cleaning performance is significantly worse. An air purifier is most effective with windows closed by continually cycling clean air in a room. To prove why it matters that windows should be closed, we tested daily for two weeks with our Coway Airmega 300S running at high speed for 30 minutes, both with windows open and closed. At the end of the test, air purifiers that run with windows closed are 40% more effective in reducing airborne particulates in a room than windows opened.

In a heavily polluted area like an industrial area or urban area, keeping windows closed can help reduce outdoor pollution by reintroducing in a room of up to 60%, according to real-world data. The only time you should leave windows or doors open is when an air purifier is not present or running. It will welcome fresh air circulating while airing out indoor air particles and smoke from cooking, dusting, and smoking.

To help you decide where to keep windows open or shut, refer to the table as a guideline.

Should You Run An Air Purifier With Windows Open?

Types Of PollutionsWindows
(With Air Purifier)
Windows
(Without Air Purifier)
Reside in a polluted area (city, industrial, mining, next to the highway)CLOSECLOSE
Outdoor air pollutions (Wildfire, haze season)CLOSECLOSE
Cooking (burned food, frying, rotten fruits)CLOSEOPEN
Smoking (cigarette, cigar)CLOSEOPEN
Chemicals fumes (VOCs, radon, ozone)CLOSEOPEN
Away from home (travel, work)CLOSECLOSE
Fire hazards that require immediate attentionOPENOPEN
Musty smell (burst pipe, leakage, after shower)CLOSEOPEN

What Happens If You Run An Air Purifier With The Window Open?

Like AC, an air purifier can still work with an open window, but it will not run as well as in a sealed room e.g. basement. The purified air will have an outlet to escape while unfiltered air from outside will be re-introduced back into the room. The air purifier will be a waste of money as it has to work non-stop, yet the purification cycle will never be completed.

Final Thoughts

We want our air purifier to perform the best when it is running day and night. There are certainly more perks with closed windows over open windows. Regardless of which side you're on, it is always better to always have an air purifier at home to clean the air. At the same time, focus on the air purifier placement, the surrounding environment, and what types of pollutants you are dealing with. As a bonus point, we compiled the best HEPA air purifier for homes that would remove airborne contaminants from inside and outside. If you are on a tighter budget, choose one of our hand-picked best air purifiers for just under 100 dollars instead.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.
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