Can Activated Carbon Remove Formaldehyde?

Can activated carbon filters remove formaldehyde and VOCs? Earlier tests from Smart Air found that carbon can reduce VOCs from cigarette smoke. But formaldehyde and VOCs in general are particular concern for many people. We put activated carbon filters to the test by ordering formaldehyde straight from the factory and … Read more

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: Obvious Town: Purifiers Most Effective With Windows Closed No one doubts … 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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DIY air purifier effectiveness blueair iqair philipps cheap god air purifier

Directly Comparable Tests: DIY vs Blue Air

I’ve wanted to know for a long time whether DIY air purifiers are as effective as the Ferrari filters.

DIY Air Purifier Cheap

In an earlier post, I compared my data to the tests of Dr. Saint Cyr (whose excellent posts inspired me to look into filters in the first place). But I noted that the comparisons were far from perfect because:

  1. The rooms were different.
  2. The Cyr post did not specify how long the tests were (and that can make a big difference if you’re looking at times under an hour–see this time comparison).
  3. The Cyr post did not describe the particle counter or particle size.

How We Tested The Air Purifiers

But now I finally have directly comparable data! That’s because two kind souls donated a Blue Air 203/270E (3,600 RMB) and a Philips AC4072 (3, 000 RMB). That means I could finally test the DIY against expensive brands in the same room, for the same amount of time, with the same particle counter.

DIY Purifier Test Method PM2.5

To do that, Anna ran 11 overnight tests with the Blue Air and 9 tests with the Philips. As always, I calculated effectiveness as percent reduction in particulates from the room air. Anna tested the air before she turned on the air filter, and then set a Dylos DC1700 laser particle counter to take hourly measurements of the air in her 15m2 room.

DIY Air Purifier PM2.5 Test

Anna used the highest setting on each purifier. (I’m putting the original data and more details about the methods for fellow nerds at the end of this post.)

And (drumroll!) here are the results:

DIY Purifier Test BlueAir Philips IQ Air PM2.5

The Cannon removed as much particulate as the expensive machines. Not bad for 450 RMB!

Yet all four filters were making the room air significantly cleaner. For particles 2.5 microns and above, all four removed over 90%. For particles 0.5 microns and bigger, all four removed over 80%. I’m not the first person to say: All you need to significantly reduce the particulate pollution in your home is a simple HEPA filter.

Based on the data, here’s how much you’re paying for each percentage reduction in 0.5 micron particles:

Price versus Effectiveness DIY Air Purifier Philips Blueair

(And that’s not counting the cost of the exorbitantly priced replacement filters.)

Recently, a Chinese news article claimed air filter companies are making “falsely inflated profits.” That fits with this data showing that the Cannon removes as much particulate as the Blueair, yet costs about 10% per percentage of 0.5 micron reduction. Similarly, the Original DIY removes 4% less 2.5 micron particulate and 6% less 0.5 micron particulate than the Blueair on average, yet the Blue Air costs more than 16 times as much.

Bottom Line: Air Purifier Test

You can remove particulate pollution from the air in your home and pay far less than a Blueair or Philips

What About Gas Pollution?

Now, as I’ve said before, particulates are not everything. There are also gases like ozone and nitrogen dioxide (although I’m less concerned about those). Here’s how to know whether your home has serious gas pollution. If it does, tests show that activated carbon removes gases like formaldehyde and benzene.

Open Data and Methods

As always, I’m posting the original data and detailed methods for fellow nerds. Don’t believe me. Check out the data and decide for yourself.

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DIY Cannon: Better, Faster, Stronger

Ever since I started my DIY filter experiments, I’ve been wondering whether I could create a super DIY by using a stronger fan. In the past three months, my collaborator Anna has helped me test a half dozen different fans. She now has a home full of fans:     … Read more

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