Tests show that even without an air purifier, keeping doors and windows closed in your house will keep particulate pollution levels at 50% the level of outdoor air. But for some, keeping windows open is a necessity. It might be that old wive’s tale that windows just have to be kept open, or perhaps you see it as a way to reduce chemicals such as VOCs and formaldehyde coming from new furniture or recent remodeling.
Can we have it both ways – clean air AND open windows? Or put it another way – do air purifiers work when windows are open? 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 Test – Air purifier vs open window
The effect of having your window open will be more prominent when outdoor air is hazardous, so CK chose two days when outdoor air was bad (February 14th and 15th) for his tests. During these two days, Beijing’s AQI averaged 239 and 290 according to the US Embassy.
To keep the baseline level of pollution consistent across tests, CK opened the window to let in outdoor air until it the indoor air pollution levels were the same as the outdoor level.
When the particle counts for indoor and outdoor air were equal, CK turned on the Cannon air purifier on high for 20 minutes. He ran three tests with the windows open and three tests with the window closed.
With the window closed, the Cannon reduced particulate by an average of 90% after 20 minutes. With the window open, the Cannon air purifier managed just a 60% reduction in particle count.
The data shows that it’s clearly better to close the windows with running your air purifier. No shocker there – we could have guessed that already! 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.
Closing your windows and turning on your purifier will give you the lowest PM2.5 levels in your home. That’s obvious.
However, if you have to balance the PM2.5 threat against high levels of VOCs or CO2 indoors, it is possible to get some ventilation AND significantly reduce PM2.5 levels indoors with your window open and purifier on.
One suggestion is you equip yourself with a super-charged purifier such as the Smart Air Blast or Blast Mini. Having your windows open whilst running a purifier like this can give you a good balance between low PM2.5 levels and low VOC or CO2 levels!
Choon Khin is a Smart Air engineer from Singapore, studying chemical engineering at the National University of Singapore