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%.
Conclusion
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.Bottom Line:
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.
Smart Air
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.
Open Data
As always, I’m publishing the raw data–all 200 days!Free Guide to Breathing Safe
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Great info about Air Purifiers, keep it up. The very informative and impressive post you have written is quite interesting. Keep sharing such valuable information.
Luckily, I live in Switzerland where the average outdoors PM2.5 is below 5ug/m3 most of the year. Still, I use an air purifier, mainly for pollens, and the occasional haze where PM2.5 jumps over even 100ug/m3.
Do you think I still have to change the filter every 6 months (manufacturer recommendation), or I can stretch longer? In other words, is it the captured particle quantity that degrades a filter or the stream of air passing thorugh it?
I’m ready to do a longevity test (with a cheap SDS011-based mobile PM2.5 counter), but I only got my air purifier a month ago so it will take time.
Good question Szak! What typically degrades the purifier performance is the amount of particles that get clogged and captured in the purifier. If your air is cleaner than say Beijing air, then it’s likely that your HEPA filter may last longer. This is why the ‘manufacturer recommendations’ aren’t very helpful – they don’t tell us whether that’s for Swiss air or Beijing air. You could also try asking the manufacturer to clarify this, or best yet (as you’ve said) – get a PM2.5 counter. Once you see that the numbers are no longer dropping to what you’d expect, it’s probably time to change your filter.
Thank you. Meanwhile I found your article about the Sqair hepa filter lab test which even has the mathematical formula, and indeed it’s the mass of the filtered pollutants that seems to matter. I’m learning extremely lot from your website, thank you for sharing all this data. And if one day Sqair will be available to buy in Europe (through Aliexpress maybe?) for a reasonable shipping cost, I’ll definitely buy one!