For the DIY purifier, I recommend replacing your HEPA filter after 140 days of use at 8 hours a day.
One of the biggest questions when I started doing the DIY was how long the HEPAs last. Rather than just give people a nice-sounding answer, I wanted to see what the data says, so I had Gus turn on his Original DIY every day in his 12.3m2 Beijing bedroom and track how effective it is each day in real Beijing air
Around Day 100, effectiveness dropped 4%. Around another Day 140, effectiveness dropped another 5-10%. But for the benefit of science, Gus risked his own lungs by continuing the test for another 60 days.
Gus turned on the Original DIY while he slept each night and tracked effectiveness using a Dylos particle counter. I calculated effectiveness as the percentage decrease in the number of particles .5 microns (and above) over the course of the night.
Here’s what a sample day looks like:
To smooth out variability over time, I averaged the effectiveness over every 10 days. For the full details on the methods, check out my earlier post.
At Day 200, effectiveness dipped to just below 50%.
At this point, at the risk of Gus’s health (especially given the coming onslaught of winter air), I voted for Gus to stop the test.
Conclusion: In real Beijing air, the Smart Air HEPA lasted at 100 days at about 8 hours a day at full effectiveness (729 hours to be exact). It lasted through 140 days (1,028 hours) with a slight 4% drop, which is when I would change the filter.
Recommendation: I recommend changing the HEPA every 140 days at about 8 hours a day or every 1,000 hours. You can adjust the number based on how many hours you use it per day.
Limitations: Gus did the test in Beijing, so HEPAs probably last a few more weeks in places with cleaner air (but still not clean air”) like Guangzhou and Hong Kong.
The results may also be different for the Cannon because it pushes more air. The next longevity test will be with a Cannon!
As always, I’m publishing the raw data — all 200 days!