“How long does a HEPA Filter last?”. “How often should I replace my HEPA Filter”. These are two common questions I got asked when I started teaching people how to build air purifiers. Rather than just give people a nice-sounding answer, I wanted to see what the data says, so Smart Air co-founder 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.
HEPA Filter Lifespan
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
The test is simple. 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 0.5 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.
HEPA Lifespan Test 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!
Learn More: How long does the Sqair’s HEPA filter last? »
Bottom Line: When to Change HEPA Filter?
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.
Recommendation: Changing the HEPA every 140 days at about 8 hours a day or every 1,000 hours.
Limitations: HEPAs probably last longer in places with cleaner air (but still not “clean air”) .
Open Data
As always, I’m publishing the raw data–all 200 days!
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