(Click here to read my new guide to choosing air purifiers in China.)



Just how much, or how little, are you willing to pay for an air purifier? Here in China expats have been so accustomed to scandalously expensive air purifiers that we get suspicious if anything’s under 4,000 RMB — which still would be more costly than almost any high end model in America or Europe. But I just finished testing a half dozen models each under 1,000 RMB, and I’m now quite convinced that the lower-priced market can offer excellent value.

I’ve tested quite a few air purifiers during my eight years here in Beijing, and I honestly thought (hoped?) I was finished with the testing. But I recently was diagnosed with asthma, which really angered me as much as it scared me. In my anxious efforts to control my symptoms, I decided to ramp up my protection from air pollution everywhere: I threw out my N95 masks and now only use N99; and I’ve totally reassessed protection at home and at work. My goal remains getting 100% of my daily exposure to PM2.5 under the healthiest target of 10 ug/m3 (AQI <50), the WHO’s official target which I blogged about last year and which I strongly feel should be everyone’s goal. I spent much of January testing more than a half dozen small air purifiers, all under 1,000 RMB, to assess which machines are best in small rooms, including my office as well as my bedrooms.

First, some background

I will repeat what I’ve said before: all you need is a good filter and a strong fan. Literally! Filter+fan. A decent filter is by far the priority, hopefully officially certified as a High Efficiency Particulate Arrestance (HEPA) filter, which in the US means 99.97% efficiency against PM0.3; the EU’s terminology is much more confusing, allowing HEPA ratings from 85% to almost 100% (more on this later). PM0.3 is short for “particulate matter of 0.3 microns size” which is essentially microscopic dust 10 times smaller than PM2.5; it’s importantly considered the most dangerous size that penetrates easiest into our lungs, causing the most harm.

While a good filter is crucial, it’s actually not super critical only to have the most awesome Hyper-Nano-Xtra-HEPA filter, with multiple 9’s that impress and overwhelm the consumer. Yes, that level of filtration is totally cool, but those extra 9’s very possibly are clinically irrelevant and only add cost, not value. Also, if the fan sucks weakly and isn’t circulating your room air at least 5 times every hour (known as ACH, “Air Changes per Hour“) then the total machine isn’t good. A machine with a 99.9999% HEPA filter but a tiny fan absolutely may clean the air less effectively than an 85% filter with a massive fan.

The same filter+fan concept applies for our ultra-expensive machines that many of us, including me, use at home for our big rooms. If they’re all humming away on a lower, noise-tolerable speed, then the air flow is much less efficient than their advertised Clean Air Delivery Rate (CADR), which refers to its max fan setting — most likely not the speed you’re always running it. Thus your rooms’ pollution may be much higher than you assume. CADR is a bit of a gimmicky test created by the industry, not a health agency, and a machine’s max setting is usually incredibly loud and which nobody uses for routine use, especially in bedrooms. The CADR test in fact is only based on 20 minutes of data! It’s a totally impractical test for consumers in China as it tells us nothing about how we all use these machines here in China — always on, 24/7, at lower, quieter speeds which don’t impede conversations or sleeping. I completely don’t care if a machine wipes out all pollen and bacteria from the air; I want to know if a machine will protect me from dying from long-term exposure to small particles like smoke and dust — at a noise level that won’t drive me crazy. That’s the data we need — and of course don’t have, at least not from the manufacturers’ ads.

Every good expensive machine is literally just an amazing HEPA filter with a strong fan. And that’s all you need — forget the rubbish about ionizers and ultraviolet light. A good machine absolutely does not have to be over 10,000 RMB, as Thomas Talhelm proved last year with his consumer-revolutionary 200 RMB do-it-yourself air purifier. His first machine was an off-the-shelf 90 RMB HEPA filter slapped with a velcro strap on top of a cheap plastic fan. And in his tests — which I confirmed on my own — it performed about as well, or better than, far more expensive machines (see his data to the right). And why wouldn’t it? His HEPA filter, if you hold a particle monitor over it, filters 100% of both PM2.5 and PM0.5; only IQAir has had similarly perfect results in my tests. You may not be ready for Thomas’ ungainly Smart Air models in your bedroom, but once you review his data you’ll certainly be much more open minded to the once heretical idea that an air purifier can be effective and affordable.

The machines

When I first arrived in Beijing over eight years ago, there were only a couple of choices for air purifiers. Now, hundreds of new models have flooded the market over the last couple of years, and I’m just as overwhelmed as you are when I search the Chinese shopping sites. There’s also very little independent testing or reviews (I wrote about one here, and here’s another). My search priorities were: price under 1,000 RMB; famous international brands > Chinese models; filter rated HEPA or darn close; fan strength flow rate (CADR) at least matching what my office needed (which is ROOM VOLUME x 5 ACH; thus 21 m3 x 5 = 105 m3/hour airflow). Another real plus was the ability to filter formaldehyde or VOCs, but that wasn’t my priority. Separate pre-filters also are helpful — but uncommon at this price point. I chose these:

Smart Air Original: 200 RMB; filters 99.9% of PM0.3; CADR unknown; covers 11-20 m2

Air-O-Swiss P320: 699 RMB; filters 99.97% of PM0.3; CADR 86 m3/h, covers 16 m2

Panasonic F-30C3PD-D: 599 RMB; filters 99% of PM0.3 and 89% formaldehyde; CADR 163 m3/h, covers 30 m2

Philips AC4025: 699 RMB; filters 91.2% of PM0.3 & 95% formaldehyde; CADR 127 m3/h

Midea KJ20FE-NH3 : 750 RMB; filters 99.9% of PM0.3 & 87% formaldehyde; CADR 204 m3/h, covers 20 m2

Xiaomi: 899 RMB (or 1,000-1200 RMB on reseller sites); filters 99.3% of PM0.3 & 91% formaldehyde; CADR 406 m3/h, covers 48 m2

My Office Results

My clinic office was the main testing ground, a cozy 9.6 square meters floor space (21.3m3 volume). For such smaller spaces, a huge Blueair or similar flagship machine would be expensive overkill and take up valuable floor space; thus my urge to test smaller models. I tested these machines over my lunch breaks, at maximum speed, with the doors closed, usually after flooding the room with outdoor air and then closing the window. My key data points were at 10 minutes and one hour (50 minutes), measuring the percentage drop in PM2.5 and PM0.5 using my completely-worth-the-cost Dylos 1700 particle monitor. During the rest of the workday I would keep them on their more standard, quieter settings and do random checks. The results are all in the table below, but the take home points are:

All machines were generally effective at my key index of PM2.5 at 50 minutes of max speed: PM2.5 reductions ranged from 88-94% . Some got there a bit quicker, and at 10 minutes the Xiaomi’s clearly larger fan definitely shows off, already clearing 88% of PM2.5 with similar results for PM0.5. Again this shows the importance of fans as much as filters, and the Xiaomi’s CADR of 406 m3/h is double the size of the nearest competitor, the Midea.

. Some got there a bit quicker, and at 10 minutes the Xiaomi’s clearly larger fan definitely shows off, already clearing 88% of PM2.5 with similar results for PM0.5. Again this shows the importance of fans as much as filters, and the Xiaomi’s CADR of 406 m3/h is double the size of the nearest competitor, the Midea. The Xiaomi needs to be clarified a bit: its max speed button only lasts 15 minutes and then reverts to auto, so its comparatively lower 50 minute data is harder to compare to the others because only the first 15 minutes are on max. But considering how at 10 minutes on max it was the leader, one could assume it would do at least as well if it had continued on max.

The Air-O-Swiss clearly was the smallest model, with a CADR of 86 m3/h not close to the 105 that I needed, and it shows in the results. But it still wasn’t too bad. Most likely their larger 350 model would be more helpful — but it exceeded my admittedly arbitrary price rule under 1,000 RMB.

The Panasonic and Philips both did fairly well — it’s just really too bad the Panasonic’s garish orange color makes it totally unprofessional for me to consider using. The Philips’ green is more acceptable, especially for a kid’s room, but still it’s not ideal.

The Midea is a nicely handsome black and white model, something I wasn’t ashamed to show in the office, unlike the two above. Its larger size and fan speed also were borne out in the generally good results, especially with PM2.5.

The Smart Air Original — the do-it-yourself 200 RMB filter and fan — performed at least as well at its more expensive cohorts, although a bit less so with the PM0.5. It’s not professional-looking enough for me to use, but it’s still a great value for students and the like, and it’s far better than using nothing at all (read my earlier review).

Noise levels on max speed wouldn’t be tolerable all day for any of the machines, but on their quieter levels were generally all OK for an office.

My favorites: I decided to test Xiaomi, Midea and Philips at home for the more important 8 hour results. I really like Xiaomi’s clearly larger capability thanks to its huge fan, not to mention its much classier, sleek look as well as its small footprint. I also thought the Philips and Midea were acceptable and not too out of place for an office.

My Bedroom Results

We’ve always used overly massive machines in our bedrooms, a Blueair 503 and IQAir Pro 150, and I thought now was the perfect time to challenge them against cheaper, smaller models (similar to my Philips test last year). This test was different than my previous tests, which had always compared indoor to outdoor air. This time, I wanted to see their efficiency over 8 hours, especially after a standard challenge by filling the room with particles, closing the doors and continuously monitoring while we slept. My particle test used essential oils in a vaporizer, which can raise the entire house’s pollution levels shockingly high and quickly. A secondary test was the final hour’s raw data: did it keep my indoor air in the green zone most of the time?

All machines this time were used on the quieter settings, not maximum as in the office tests. The great majority of tests were run in the larger master bedroom, which at 40 m3 (16 m2) needs airflow of 200 m3/hour. The smaller bedroom is 23 m3 (10 m2) and needs airflow >115 m3/hour.

Just for fun, I also compared these against an Airgle AG800, a much larger machine whose massive airflow of 763 m3/h easily should clean the air in such small rooms even at lower fan speeds.

The results, please

At the crucial 8 hour mark , most machines performed quite well. For PM2.5, Blueair led the way at 99.9%, just edging out Xiaomi’s sleep mode at 99.8%, with most others close behind in 98-99% range. For the smaller PM0.5, Blueair again topped out at 99.9%, closely followed by Philips at 99.6 and Xiaomi at 99.5%.

, most machines performed quite well. For PM2.5, Blueair led the way at 99.9%, just edging out Xiaomi’s sleep mode at 99.8%, with most others close behind in 98-99% range. For the smaller PM0.5, Blueair again topped out at 99.9%, closely followed by Philips at 99.6 and Xiaomi at 99.5%. For short-term clearing within 1 hour , the Airgle did very well as you would expect for its huge fan, designed for much larger rooms. Otherwise, the budget machines from Xiaomi on auto and the Midea on low speed also did very well. (But the Xiaomi on auto comes at a slight cost, as its higher speeds to fight the incense are a bit louder and temporarily a bit distracting. And the Midea on low is a bit too loud for sleeping; fortunately the quieter sleep mode also did fairly well.)

, the Airgle did very well as you would expect for its huge fan, designed for much larger rooms. Otherwise, the budget machines from Xiaomi on auto and the Midea on low speed also did very well. (But the Xiaomi on auto comes at a slight cost, as its higher speeds to fight the incense are a bit louder and temporarily a bit distracting. And the Midea on low is a bit too loud for sleeping; fortunately the quieter sleep mode also did fairly well.) Another useful metric is the final hour’s raw data (particles per cubic foot/100) : My goal for PM2.5 is to always have the Dylos data stay under 50, which is roughly equivalent to 10 ug/3 (or AQI<50). The great news is that every machine’s final ranges were far under 50, including both cheaper models. For the trickier to control smaller PM0.5, the goal is a bit less clear but Charlie Thompson from my environmental testing company Environment Assured agrees that Dylos PM0.5 under 1,000 is the best equivalent to AQI<50. Using this cutoff, both the Philips and Blueair did extremely well, followed again by Midea and then Xiaomi in third. The larger machines from Airgle and IQAir surprisingly had some data over 1,000 — the only machines to do so.

: My goal for PM2.5 is to always have the Dylos data stay under 50, which is roughly equivalent to 10 ug/3 (or AQI<50). The great news is that every machine’s final ranges were far under 50, including both cheaper models. For the trickier to control smaller PM0.5, the goal is a bit less clear but Charlie Thompson from my environmental testing company Environment Assured agrees that Dylos PM0.5 under 1,000 is the best equivalent to AQI<50. Using this cutoff, both the Philips and Blueair did extremely well, followed again by Midea and then Xiaomi in third. The larger machines from Airgle and IQAir surprisingly had some data over 1,000 — the only machines to do so. In overall performance , all three cheaper machines certainly held their own, and none of them were obviously inferior even to the larger machines. The Midea posted impressive data even on their very quiet sleep mode. The Xiaomi also performed very well long-term and also was the best with short-term air clearing when in auto mode. The Philips also performed quite well with some very low raw data (but the outdoor air also was quite good that night, which helps a bit). For the three larger, far more expensive machines which on paper should have blown away their cheaper competition, only Blueair’s performance seemed obviously strongest, with the lowest raw data of all the machines in both particle sizes.

The Midea posted impressive data even on their very quiet sleep mode. The Xiaomi also performed very well long-term and also was the best with short-term air clearing when in auto mode. The Philips also performed quite well with some very low raw data (but the outdoor air also was quite good that night, which helps a bit). For the three larger, far more expensive machines which on paper should have blown away their cheaper competition, only Blueair’s performance seemed obviously strongest, with the lowest raw data of all the machines in both particle sizes. CORRECTION March 18: new data from the incredible Dylos FAQ at aqicn.org suggests that the left side number, PM0.5, actually is more representative of actual PM2.5 and the right side number represents PM10. Other data suggests that my PM0.5 goal of 1,ooo equals an AQI of 18 which actually is a bit of overkill; at 3,000 it equates to AQI of 53, just above the “green zone” of 50 (which equals a PM2.5 concentration of 12 in the USA). So anything under ~2,500 seems all to be in the green zone — which is great news as all my final hour raw data for PM0.5 was under 2,00 and often much less)

My choices

For my office, my decision was fairly easy: I decided to go with Xiaomi due to performance, price and professional look. The Midea isn’t a bad second choice.

For the bedrooms, my decisions have been a lot harder. Since I already had machines, I’d need a really good reason to replace them. For the new bedroom, I’ve decided to use the Xiaomi. For our other bedrooms, I’m still deciding but know I will replace the IQAir and possibly also the Blueair with either the Midea or the Xiaomi.

I must talk a little bit more about Xiaomi’s air purifier, which is only on the market for three months but clearly may be very disruptive to the industry due to its novel design and incredible price. One very cool thing about Xiaomi which separates it from all the other machines is their app; their machines have built-in wifi which you can link inside their smart phone app and control the speed as well as get real-time data on the pollution inside the room, compared to the pollution outside (based on China MEP hourly data). This app even sends your phone an SMS telling you “the outdoor air is now clean and better than indoor air, it’s time to open the windows”! It also gives you real-time estimate of remaining filter life. It’s extraordinarily cool, even if a bit gimmicky — but this is my first foray into the exploding “connected home” phenomenon of intelligent, wifi-enabled home appliances, and I can definitely see the value in such data.

But I do have some reservations about Xiaomi, mostly because it’s a newish company known mostly in the mobile phone market for value, not so much top quality. Their HEPA filter is advertised as H11, which they claim is 99.3% efficient, which is not the highest rated top-line HEPA of 99.97%; but clearly their massive fan more than compensates for this, which accounts for its essentially similar, sometimes superior, results to the more expensive machines. As I said before, it’s the combination of fan+filter that’s the key.

Other negatives about Xiaomi are the newness of the machine. Since their air purifier is only a few months old, there’s no track record on maintenance or reputation. It’s also extremely difficult to buy on their own website due to their very unusual direct-selling marketing techniques; you can’t just order it, you have to first click to “reserve” and then on Tuesday at noon you and thousands of other people return to the website to buy, first come first served. I tried twice and they were sold out within one minute, so I was forced to use third-party resellers on Jingdong and Tmall — marked up, of course. This limited availability really disturbs me — what if the refill filters become hard to find?

These uncertainties are the main reasons why I didn’t replace my entire house with Xiaomi; otherwise, their price point and value are exactly the kind of disruptive innovation that the air purifier market in China desperately needs.

The Bottom Line (Finally!)

To summarize, I hope I’ve demonstrated that there are indeed many air purifiers far, far less than 10,000 RMB which may be perfectly adequate for your smaller room needs. Maybe 1,000 RMB models are a bit too weak, and for 1,500-3,000 RMB you can get a stronger fan and filter, especially from international companies with long track records such as Panasonic, Philips, Westinghouse and others.

Please note that my tests should serve as a guide, not as a strict recommendation, for your own decision-making. I also hope many readers also test their machines and share results with others, as Thomas does. My main hope is that people who currently don’t use any machine, mostly due to cost, will now realize they have far more options than they previously thought.

Other versions: Translation into Portuguese; Estonian;

on Facebook: @BainbridgeBabaDoc Photography: www.richardsaintcyr.com