Tests show that keeping the doors and windows closed will keep particulate levels at 50% less than outdoor air on average. But some people really want to keep their windows open. For some people, it’s an old wive’s tale that windows must be kept open. For others, it’s a way to reduce chemicals coming from new furniture or recent remodeling.
Can we have it both ways? Or are our purifiers useless with when our windows are open? CK from the Smart Air team put this question to the test by running the DIY Cannon in the 12m2 Smart Air testing room six times.
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 reached the outdoor level.
When the particle count reached the same level as outdoors, CK ran the Cannon 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 managed just a 60% reduction in particle count.
The data shows that it’s clearly better to close the windows. 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 a purifier.
Closing your windows and turning on your purifier will give you the lowest PM2.5 levels in your home.
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.
In other words, having the windows open does NOT mean turning on your purifier will be useless. It may mean it takes longer to bring the PM2.5 levels below the safe limit (or it might not even be possible), but it is definitely still an improvement over no purifier.