One of the biggest questions when I started doing the DIY was HEPA lifespan–how long do the HEPAs last? Rather than just give people a nice-sounding answer, I wanted to see what the data says, so Gus has been dutifully turning on his Original DIY every day in his 12.3m2 Beijing bedroom and tracking how effective it is each day in real Beijing air
Around Day 100, effectiveness dropped 4%. Around another Day 170, effectiveness dropped another 5-10%. But for the benefit of science, Gus has risked his own lungs by continuing the test for another 60 days.
HEPA Lifespan Test Method
Gus turns on the Original DIY while he sleeps each night and tracks effectiveness using a Dylos particle counter. I calculate effectiveness as the percentage decrease in the number of particles .5 microns (and above) over the course of the night.
Here’s what a normal 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.
HEPA Lifespan Results
The death crawl continues. At Day 200, effectiveness dipped to just below 50%.
At the risk of Gus’s health (especially given the coming onslaught of winter air), I voted for Gus to stop the test. So the test is over!
In real Beijing air, the Smart Air HEPA effectiveness decreased by about 20% after 150 days (1,109 hours), which is when I would change the filter.
I recommend changing the HEPA every 150 days at about 8 hours a day or approximately every 1,000 hours. You can adjust the number based on how many hours you use it per day.
Limitations: We 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.
Read more: Check out how the real-world Sqair HEPA longevity test compared to official lab tests.
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