When I published tests of the DIY compared to the expensive machines, a couple people on Zhihu (China’s Quora) asked if you really save money in the long run with the DIY once you calculate the cost of changing the HEPA. After all, the IQ Air HEPA costs 1,782 RMB, but you can use it for more than a year.
Long-Term DIY HEPA Costs
At that time I didn’t have an answer. To get an honest answer, I needed to do tests in the real world, but that took almost a year to complete. (That’s more than I can say for the numbers IQ Air and Blue Air give. If filters last 6 months in Sweden, are they going to last 6 months in Beijing?)
Now it’s a year later, and I have that data. Smart Air co-founder Gus ran his Original DIY for eight hours a day and tracked what percentage of particulate it removed from the air each day with a Dylos particle counter.
Based on that data, I recommend changing HEPAs after 140 days at 8 hours per day (about 1,000 hours of use). Since that HEPA costs 80 RMB, that averages to .57 RMB per day and 208.6 RMB per year.
To get an idea of what that means, we can compare that to the cost of drinking a bottle of water a day:
Big Brand HEPA Costs
I’m highly skeptical that HEPA recommendations for Sweden can be mapped onto China. But to be conservative, I’ll assume in my calculations that their numbers work the same in China.
I calculated costs for the Blue Air 203 and IQ Air Health Pro Plus using the same conditions I used for the Original DIY longevity test:
- Highest setting
- 8 hours of use per day
- Extend those costs over a year
- Include the cost of pre-filters but not carbon filters
Blue Air’s HEPA costs 300 RMB and lasts 6 months. That works out to 1.67 RMB per day and 609.6 RMB per year.
IQ Air’s HEPA is more expensive: 1,782 RMB. On the sixth setting, it lasts 4,968 hours. If you use it 8 hours a day, that works out to 2.87 RMB per day and 1,047.4 RMB per year.
However, we have to add the cost of the pre-filter because the HEPA lifespan depends on the pre-filter. The pre-filter costs 645 RMB and lasts 2,016 hours on the sixth setting. That works out to 2.56 RMB per day and 934.3 RMB per year.
IQ Air grand total: 1,982 RMB per year.
The long-term HEPA cost for the Original DIY is 66-89% less than the Blue Air and IQ Air.
It should be noted that these results may not map onto the Cannon. I’m still working on the Cannon longevity test, so we’ll need to wait until that test is done.
As always, I’m writing more details about the data below for fellow nerds.
Extra Data and Methods
DIY HEPA Costs
DIY HEPA costs are based on the 200-day longevity test in real Beijing air. All 200 days of original data are available in that post.
IQ Air Costs
One thing to note: the calculations above are based on the sixth setting. If the IQ Air runs on setting three, the effectiveness will be lower, but the HEPA will last longer. In my calculations, I totaled the costs for one year one setting three: 901 RMB. That’s lower than the calculation above (because it’s processing less air), but it’s still more than four times the cost of the DIY HEPA.
Blue Air Costs
Calculating costs for the Blue Air is more difficult. That’s because Blue Air doesn’t seem to publish longevity recommendations for different settings or how many hours you can use the HEPA. Instead, Blue Air says you should replace the HEPA after six months.
Thus, I sent Blue Air an email asking how many days I should replace the HEPA if I run my machine eight hours a day. A Blue Air representative told me six months and told me I would void the warranty if I used it more than six months. Thus, I used their recommendation in my calculations (original email).
If Blue Air is wrong and the HEPA lasts long at eight hours per day, the calculation changes. I have alternative calculations here.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.