When I did my first experiments, several people told me not to publish the data. “Don’t give it away for free,” they told me. “Use it to make money!” I decided then that my main goal wasn’t to make money. I almost got tricked into paying $1,000 for clean air, and I wanted to help people avoid getting tricked too, so I published the data anyway.
Of course, publishing the instructions online has made it easy for people to copy the idea. The Huanwo Lantian (还我蓝天) was one of the first to follow in our footsteps, selling a DIY filter a few months back. They even use a screen capture of Smart Air co-founder Gus’s appearance on Chinese TV on their shop:
I was curious to see how their filter works, so I decided to order one off of Taobao and put it to the test.
Now I’m in an awkward position because I found that their HEPA was not working nearly as well as my Smart Air HEPAs. It’s awkward because, if I publish the data, will people think I’m just trying to attack a competitor?
In the end, I think it’s better to publish the results and be honest about my conflict of interest. At the very least, I think people have an interest in knowing how well other DIYs work–especially when some of those websites use graphs that are lifted from my site, which can mislead people into thinking the test results are from their machines.
And as always, I’m publishing my raw data and testing methods at the end of this post, so fellow nerds can replicate my studies.
DIY Purifier Test Method
My collaborator Anna used the same methods as our earlier tests in her 15m2 room. Anna did five overnight tests with the same Dylos Pro particle counter, and I calculated effectiveness as the percent reduction of particles in the room air, averaging the last three hours (more info). Then I compared the results to my earlier tests in the same room.
Imitation DIY Purifier Results
The Huanwo Lantian DIY removed 21% fewer particles 0.5 microns and above and 11% less 2.5 micron particles than the Original DIY.
Is It The Fan?
The Huanwo Lantian fan is slightly smaller than the Smart Air Original, so one explanation could be that the fan is just moving less air. Anna tested that by strapping the Huanwo Lantian HEPA onto our Original fan.
Here’s what that test showed.
There wasn’t much difference. With the new fan, it was getting 4% more 0.5 micron particles and 2% less 2.5 micron particles. Thus, the fan doesn’t seem to be the reason.
Is It The HEPA Filter?
The second possibility is that the Huanwo Lantian HEPA isn’t as good. Anna tested the HEPA by doing air outlet tests with a Met One GT-521, which measures down to 0.3 microns. Anna tested the air coming out of the HEPA for 10 seconds, and I averaged the results from three tests. (More details at the end of the post.)
The Huanwo Lantian HEPA captured 7% fewer particles that the Smart Air HEPA. Thus, the major source of the poor performance of the Huanwo Lantian seems to be the quality of the filter.
Now, don’t get me wrong. The Huanwo Lantian DIY purifier is making the room air cleaner. It demonstrates yet again that DIY air purifiers work. I’d rather have a Huanwo Lantian than nothing. But the results show that this DIY copycat is cutting corners by using cheap HEPAs.
As always, I’m posting the raw data and more detail on the methods for fellow nerds.