HEPA Lifespan: Longevity Test Day 200

HEPA Lifespan Test Filter Air Purifier

One of the biggest questions when I started teaching people how to build DIY purifiers is “how long is the HEPA lifespan?” 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.

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.


Replace dirty HEPA filter


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.


Dylos particle counter test


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:

HEPA Longevity 200 Day Test - Sample Example Day

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%.

HEPA Filter Longevity Test 200 Days Longitudinal


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!


HEPA Lifespan: Bottom Line

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: 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.

Open Data

As always, I’m publishing the raw data–all 200 days!

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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… Read more »

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… Read more »


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!