Do Air Purifiers Work With the Window Open?

Will my air purifier still work if I have a window open? New test data from Smart Air finds that air purifiers can still meaningfully reduce particulate pollution in a room with a window cracked.  Here’s what to know: The Obvious: Air Purifiers Most Effective With Windows Closed No one … Read more

New DIY Purifier Design Increases CADR 15%

After I made my first DIY purifier, a design magazine called me up to interview me. I said, “You realize this has no design in it, right? It’s just a fan and a filter.” Now I actually have a design improvement! I’m calling it the DIY 1.1.  The Problem The … Read more

New DIY Design Increases CADR 15% – Supplemental Data

Methods Results were identical to my earlier tests of the Original DIY, Blue Air, IQ Air, Xiaomi, and Philips. Anna conducted the overnight tests in her 15m2 Beijing bedroom. Doors and windows were closed during the test (except for occasional opening during the first couple hours before bed—that random variation … Read more

Car Air Pollution Stopped Driving

Do We Need Car Air Purifiers? Do they Work?

Car air purifiers sound like a great idea. But do we need them? Do car air purifiers even work?  Soon after I started making DIYs, people emailed me asking if we could make an air purifier for their car. My initial reaction was, “Great idea!” On the highways, we’re surrounded … Read more

Is It Possible to Lower the Cost of Clean Air Without Sacrificing Effectiveness?

A few months after I published my DIY tests, there were already Taobao stores up and running, selling DIYs even cheaper than my 200 RMB. I was intrigued. If we could really lower the cost of clean air, that’s a win!

But we have to be sure these cheaper machines are as effective. So I ordered the cheaper machines, tested them systematically, and found they performed much worse (2).

A New Way to Lower the Cost of Clean Air

But that doesn’t mean there aren’t ways to make HEPAs even more affordable. Recently I tested one way to do that: if we can shave 1 millimeter from the size of the HEPA, we can save 6% on the price. This new size still covers the fan opening, but does it still work as well?

Method

To test this question, my collaborator Anna ran 10 overnight room tests with the 290cm in her Beijing apartment and compared it to my earlier tests of the 30cm HEPA in the same 15m2 room.

e

Like in my earlier tests, I calculated effectiveness as the percent reduction in particulate from the start of the test to the average of the last four hours. Here’s what one of those tests looks like with the reduction calculation laid out. The blue line is indoor 0.5 micron particles; the red line is outdoor PM 2.5

q

Results

On average, the new 29cm HEPA reduced 0.5 micron particle levels in the room by 86% and 2.5 micron levels by 91%. These results were almost identical to my prior results with the 30mm HEPA.

w

Conclusion

This new HEPA lets us lower the cost of clean air without sacrificing any effectiveness. Win! We just lowered the price of Smart Air HEPAs from 80 RMB to 75 RMB.

HEPA Cost Comparison

Next I took that price and compared it to the two biggest brands out there, Blue Air and IQ Air. (Also check out the long-run cost comparison .)

Nerd Note on Replication

As a side note, this test is now the third series of room tests I’ve published with the Original DIY (early tests; 200-day longevity test). Add that to Dr. Saint Cyr’s tests, and I’d say that’s a satisfying amount of reproducibility.

For fellow data nerds, I’m posting the original data and more details about the test below.

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DIYer Makes Cannon Quieter

Bill is an expat living in the hills northwest of Beijing, and he uses his DIY Cannon to cut the particulate in his home. But Bill wanted to improve on the biggest downside of the Cannon–it’s a bit loud on high: So Bill designed a sound dampening box for the Cannon … Read more

Preparing for Air Pollution in Ulaanbaatar, Mongolia

Air purifiers and air pollution are probably the last things that come to mind when thinking of Mongolia. But maybe it should be the first, given how bad the air there is. I was living in Beijing during the airpocalypse, so I decided to buy an air purifier. Then I discovered … Read more

Are DIY Purifiers Still Cheap in the Long Run?

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, … Read more

Can DIY Air Purifiers Clean Large Rooms?

Can DIY air purifiers clean large rooms? Hundreds of hours of Smart Air tests have found that DIY air purifiers cut fine particulate, reduce smoke, remain effective over 200 days, and even capture chemicals like formaldehyde. But an important practical question is whether DIY purifiers are effective enough to purify large rooms.

DIY Air Purifier Search

To answer this question, I tested every fan I could find, as long as it had a flat front. I was looking for a fan that put out a lot of air.

After getting all the data, of one fan stood out above the rest. I called it “the Cannon.”

In Anna’s 15m2 Beijing bedroom, it crushed particulates. It removed 97% of the small .5 microns particles.

But how well can it do in larger rooms? Most companies estimate this using flow rate, but those calculations depend on how well houses are sealed and how dirty the air outside is. I wanted to know how well a DIY air purifier can clean under real-world conditions.

DIY Air Purifiers Clean Large Rooms: The Test

I tested the Cannon on its high setting six times in a 30.5m2 living room–a large, open space. To track pollution, I measured 0.5 and 2.5 micron particles using a Dylos laser particle counter. Each test lasted at least three hours.

DIY Air Purifiers Clean Large Rooms Test Setup

I calculated the percentage reduction in particles from the first hour to the last hour.

DIY Air Purifier Clean Large Rooms Test Cannon

Besides testing in a big space, this experiment extends the findings of the earlier room tests because:

1. These tests were run in the daytime. Several people have the intuition that pollution goes down at night because people are less active and fewer cars are on the road (but the data shows that intuition is false–PM2.5 pollution is worst in the middle of the night in Beijing).

 

2. These tests were run while people were moving around in the room and opening the door to the outside. This is more conservative than the nighttime tests because the Cannon has to fight influxes of outdoor air.

DIY Air Purifiers Clean Large Rooms Effectively

Over six tests, the Cannon removed 92% of .5 micron particles and 89% of 2.5 micron particles even with people moving around and opening doors.

In previous tests, 2.5 micron reductions were usually slightly larger than .5 micron reductions, so it’s a little surprising that the 2.5 micron reduction was 3% lower than the .5 micron reduction. My guess is that this is because people were moving in the room, and human movement affects the 2.5 micron readings much more than the .5 micron readings.

Bottom Line:

With a fan as strong as the Cannon, DIY air purifiers clean large rooms effectively, reducing 0.5 micron particles 92% on average.

As always, I’m posting the raw data and more details on the methods for fellow nerds below.

 

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Smart Air is a social enterprise that creates simple, no-nonsense air purifier and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.