UPDATE, March 2015: Please check out my 2014 review of the science behind air purifiers; my 2015 tests of air purifiers under 1,000 RMB plus my 2014 review of two dozen top air purifier models in China.
We’ve just survived yet another winter night with the US Embassy’s air pollution AQI maxed out “beyond index” over 500, so it’s again a good time to review one of Beijing life’s unfortunate necessities: indoor air purifiers. In our expat world’s never-ending discussion of the best air purifiers, many of you have read my article detailing my head-to-head battle of IQAir 250 Pro versus Blueair 501. Now we can add a third player in my personal tests: Alen Air. Alen Air is a Texas-based company which makes air purifiers, and a couple months ago their local rep invited me to test out (not keep!) two of their machines at my house: their flagship A375UV machine, and also their Paralda unit. So I spent a couple days comparing these brand-new machines with my trusty stalwarts, my IQAir and Blueair.
First, The Boring Tech Stuff
It’s very important to know that my home’s machines did not have new filters, so true comparisons to these new Alen Air machines cannot be done. My Blueair’s filters were at least 4 months past prime, and my IQAir’s pre-filter was in the red zone. (Still, their data is also interesting). Anyway, I spent a few days wheeling around each machine in one of 4 rooms:
- library, small bedroom and master bedroom: each around 10-12 square meters
- front living room, itself 30 square meters and open into a large hallway and dining room, with no doors
I then measured each room’s pollution levels with a handheld Particlescan machine. This machine measures PM0.3 particles, which are much smaller than the PM2.5 which the US Embassy monitors. These tiny particles are what most scientists think are the causes of pollution-related lung and heart disease, as they easily get absorbed into the blood stream via the lungs.
I was “lucky” enough to be testing on days with the US Embassy readings in the high 200’s, so this was definitely a real-world challenge for any purifier.
The Real World Results
The good news is that both Alen Air purifiers did quite well, and indeed better, than last year’s tests of the IQAir and Blueair. For example, on average:
- The A375 filtered out 94% of PM0.3 (96% at max setting) compared to the unfiltered part of my house (the hallway and back rooms); this was the best number I’ve had for any machine
- The Paralda filtered out 80% (83% at max), also very good
- My oldish-filtered IQAir filtered 76%
- The older-filter Blueair filtered 66%
Another very positive point is that all purifiers did really well in bedrooms with doors closed. In fact, all four machines at maximum settings removed 95-99% of PM0.3! At quieter settings it was less awesome but still very good. I think this is powerful proof that air purifiers in bedrooms can dramatically reduce your pollution risk while you sleep — an issue especially crucial for infants and children.
In last year’s results from my previous apartment:
- The IQAir filtered 74% on average, 84% at max setting
- The Blueair 501 filtered 74% on average, 82% at max setting
- In the small bedroom with closed doors, IQAir filtered 79%, blueair 73%
- In the larger, open dining room, IQAir filtered 61%, Blueair 67%
Compared To Outdoor Air? Awesome
Don’t forget that the above numbers are comparing filtered rooms to a “control” room in a separate part of the house. So if you compare these above numbers to outdoor air, they perform even better. For all readings, I also stuck the Particlescan out of my 15th floor window and recorded this data.
On average, indoor air PM0.3 in my unfiltered hallway was 53% of outdoor air. I think that’s pretty good, and it’s a lot better than my previous apartment a couple years ago, which usually was around 70%. I think it shows how proper ventilation and window protection can help.
But what that also means is that these machines did even better than the numbers above. For example, if you’re comparing each room to outside air, the A375 got rid of 97% of anything bigger than PM0.3. Also:
- Small rooms with closed doors were 95-99% cleaner than outdoor air
- Open, large room was 29-39% cleaner than outdoor air
Don’t Forget Hunter, and Others
Last year I also wrote about a smaller and cheaper HEPA filter from Hunter, which in my readings routinely eliminated 50-70% of PM0.3 pollution even with the constant door opening in my 12-square meter office. At max speed with the door closed for a while, it got 91% of the pollution.
The Bottom Line
Clearly, with good filters, all these machines do really well in smaller rooms with doors, and I’m sure a bunch of other HEPA brands may also be ok. The larger rooms are always more difficult for all, but for the most important room — your bedroom — many HEPA models will probably be fine. Major differences between HEPA models include:
- Room size
- Replacement filter costs
- Resale value
- Other “features” (ozone, UV, remotes…)
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