Will my air purifier still work with a window open? Recent test data from Smart Air, air purifiers can still significantly reduce PM2.5 in a room even when a window is slightly cracked. Here’s what you should know:
The Obvious: Air Purifiers Most Effective With Windows Closed
No one doubts that purifiers are most effective with the windows closed. That’s obvious. Real-world tests show that – even without an air purifier – simply keeping doors and windows closed keeps particulate pollution levels at 50% of the level of outdoor air.
But the more practical question is, if I have to keep a window open for some other reason, will running a purifier still work? Will it have a meaningful effect? For some people, keeping windows open is a necessity. You might want to keep your windows open to reduce chemicals such as VOCs and formaldehyde in your home or office. Others might want to keep a window open to ventilate out CO2. In addition, new studies show COVID-19 spread is reduced drastically when both filtration and ventilation are used together.
The Test: Air Purifier vs. Open Window
Can we have it both ways – clean air AND open windows? CK from the Smart Air team put this question to the test by running the DIY Cannon air purifier Smart Air’s 12m2 Beijing test lab six times with the window open and closed.
The effect on indoor air pollution levels of having your window open will be more prominent when outdoor air is hazardous, so CK chose two days when outdoor air pollution was bad (February 14th and 15th) for his tests. Beijing’s AQI averaged 239 and 290 during these two days according to the US Embassy.
To keep the baseline pollution level consistent across tests, CK opened the window to let in outdoor air (and outdoor air pollution) until the particulate pollution was the same as outdoors. Then, CK turned the Cannon air purifier on high for 20 minutes. He ran three tests with the windows open and three with the windows closed.
Results: Can You Use an Air Purifier with the Window Open?
With the window closed, the Cannon air purifier reduced particulate by an average of 90% after 20 minutes (blue lines). With the window open, the Cannon air purifier managed a 60% reduction (red lines).
The data shows that it’s clearly better to close the windows while running your air purifier. No shocker there!
But here’s the more interesting part: even with the windows open, it’s still possible to significantly reduce indoor particulate by turning on an air purifier.
Turning on the air purifier with the window open still reduced pollution levels by 60% within 20 minutes.
How to Use Air Purifier with Window Open
The best way to use an air purifier with the window open is to use a purifier that’s rated for a larger area than your room size. We do this in the Smart Air office by using the super-charged Smart Air Blast, which cleans up to 130m2. Here it is kicking butt in Beijing while the window is open.
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How do you balance out the benefit of constant ventilation with keeping windows closed to purify the air better? I’ve read that we need complete air changes every few hours otherwise co2 rises and air becomes more stale etc but I’m really struggling to determine if closing the windows, assuming fair conditions outside(London), is worse than having a steady flow of fresh air coming in. I’ll probably need the windows open more now that summer is arriving too. Thanks
“Simply keeping doors windows closed keeps particulate pollution levels at 50% the level of outdoor air” – because your lungs purified it.
I was exposed to toxic levels of Formaldehyde when the person who owned the apartment before me put down floors that were bought from lumber liquidators. During that time they were importing floors from China that Were contaminated with up to 100 times the California legal limit of Formaldehyde. I replace the floors and bought an AirpuraAir purifier I took all of my lamps with their lampshades out of my room and even my stereo speaker. Is there anything else I should be doing? I am tired of blowing my nose into seventh generation tissues which supposedly have no Formaldehyde,… Read more »
Thanks for this. Down here in Hong Kong, the pollution levels aren’t usually as dramatic as those of Beijing, but they’re certainly nothing to be satisfied with. The willful ignorance of many Hong Kongers and obsession with “ventilation”, coupled with the government’s distorted AQHI which doesn’t reflect international standards, means that people nonchalantly keep windows open when they really shouldn’t. I’m the only foreigner in my workplace and am really struggling with colleagues who insist on windows being open to let in the “fresh” air now that it’s cooling down, which is when the pollution really sets in. I’ve got… Read more »
Thanks for taking the time to do this useful test. regards Tim of Australia