DIY cloth masks to protect against viruses sounds like a crazy idea. Data shows masks work incredibly well, and they’re also really cheap. Surgical masks cost a few pennies, and they’re capable of filtering out 80% of particles down to 0.007 microns (14 times smaller than COVID-19). However, the COVID-19 … Read more
New head-to-head test data from a citizen scientist finds that a simple, taped-together DIY air purifier effectiveness is higher than a market-leading Swiss air purifier, IQ Air. This data adds to an accumulation of data suggesting that effective air purifiers need not be expensive. The Setup The underlying science of … Read more
In the rush to make homemade masks, many people are wondering whether reusable bags such as non-woven polypropylene plastic bags are effective at filtering viruses. These reusable bags are incredibly popular in places like Asia and Africa, where they are a common alternative to flimsy plastic shopping bags. Why Non-Woven … Read more
In a recent study, researchers tested household materials that could be used to make DIY masks, but they left out one common material—paper towel masks (also called “kitchen paper”). Could paper towel be an effective material for making homemade masks in times of crisis and shortages? Smart Air Engineer Paddy … Read more
With masks sold out during the coronavirus outbreak, many people will have to make do with what some scientists have called “the last resort”: the DIY mask. Data shows that DIY and homemade masks are effective at capturing viruses. But if forced to make our own mask, what material is … Read more
When I was coughing through Beijing’s airpocalypse and thinking about buying an air purifier, I wanted to know something first–do air purifiers really remove PM2.5? I wondered because I saw lots of air purifier tests on pollen, but pollen is generally 10 microns or larger, whereas I was … Read more
Should air purifiers have the filter on the front or the back–is it better to push or pull air? The Smart Air lab in Beijing ran tests of the same fan with the HEPA filter on either side, and the results contradict most people’s intuition. When I made my first … Read more
I recently published tests showing that carbon actually removes VOCs. But adding that carbon layer raises a question: adding carbon means the fan has to power through yet another layer of resistance. Does that make purifier less effective at removing particulates?
I measured how much particulate it removed with a Dylos particle counter and compared the particle counts (1) before I turned on the purifier at night and (2) the average of the last four hours before I woke up in the morning.
Carbon vs. HEPA Results
With the additional charcoal layer, the Cannon particulate effectiveness dropped 1-2%. Thus, charcoal has a very minor negative effect on the Cannon.
However, the Original DIY had a harder time powering through the extra layer. Its 0.5 micron effectiveness dropped 19%, and 2.5 micron effectiveness dropped 15%.
Conclusion: Carbon Tips
For people who need carbon (and that may not be everyone), I would recommend adding the carbon to the Cannon, but I would think twice about adding carbon to the Original. One workaround is to have one Original fan running with a HEPA and another running with a carbon filter.
As always, I’m posting the raw data and more details on the test for fellow nerds below.
I’ve wanted to know for a long time whether DIY air purifiers are as effective as the Ferrari filters.
In an earlier post, I compared my data to the tests of Dr. Saint Cyr (whose excellent posts inspired me to look into filters in the first place). But I noted that the comparisons were far from perfect because:
The rooms were different.
The Cyr post did not specify how long the tests were (and that can make a big difference if you’re looking at times under an hour–see this time comparison).
The Cyr post did not describe the particle counter or particle size.
How We Tested The Air Purifiers
But now I finally have directly comparable data! That’s because two kind souls donated a Blue Air 203/270E (3,600 RMB) and a Philips AC4072 (3, 000 RMB). That means I could finally test the DIY against expensive brands in the same room, for the same amount of time, with the same particle counter.
To do that, Anna ran 11 overnight tests with the Blue Air and 9 tests with the Philips. As always, I calculated effectiveness as percent reduction in particulates from the room air. Anna tested the air before she turned on the air filter, and then set a Dylos DC1700 laser particle counter to take hourly measurements of the air in her 15m2 room.
Anna used the highest setting on each purifier. (I’m putting the original data and more details about the methods for fellow nerds at the end of this post.)
And (drumroll!) here are the results:
The Cannon removed as much particulate as the expensive machines. Not bad for 450 RMB!
Yet all four filters were making the room air significantly cleaner. For particles 2.5 microns and above, all four removed over 90%. For particles 0.5 microns and bigger, all four removed over 80%. I’m not the first person to say: All you need to significantly reduce the particulate pollution in your home is a simple HEPA filter.
Based on the data, here’s how much you’re paying for each percentage reduction in 0.5 micron particles:
(And that’s not counting the cost of the exorbitantly priced replacement filters.)
Recently, a Chinese news article claimed air filter companies are making “falsely inflated profits.” That fits with this data showing that the Cannon removes as much particulate as the Blueair, yet costs about 10% per percentage of 0.5 micron reduction. Similarly, the Original DIY removes 4% less 2.5 micron particulate and 6% less 0.5 micron particulate than the Blueair on average, yet the Blue Air costs more than 16 times as much.
Bottom Line: Air Purifier Test
You can remove particulate pollution from the air in your home and pay far less than a Blueair or Philips
How can we make a homemade DIY air purifier? Air purifiers can be extremely expensive. But they don’t need to be. After researching how different air filters work, I concluded that a HEPA filter is all that’s needed to make an effective air purifier. Given that most air purifiers sell … Read more
Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.