The Best Air Purifiers Under 1,000 RMB: My Test Results

(Click here to read my new guide to choosing air purifiers in China.)
Shanghai Skyline in thick Fog

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

Particles and sizes

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 ) 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, ““) 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 (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.

Smart Air vs. Famous Brands

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 slapped with a velcro strap on top of a cheap plastic fan. And in — 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  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 ). 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:

midea philips panasonic air purifiers
Midea, Panasonic, Philips
  • : 200 RMB; filters 99.9% of PM0.3; CADR unknown; covers 11-20 m2
  • : 699 RMB; filters 99.97% of PM0.3; CADR 86 m3/h, covers 16 m2
  • : 599 RMB; filters 99% of PM0.3 and 89% formaldehyde; CADR 163 m3/h, covers 30 m2
  • : 699 RMB; filters 91.2% of PM0.3 & 95% formaldehyde; CADR 127 m3/h
  • : 750 RMB; filters 99.9% of PM0.3 & 87% formaldehyde; CADR 204 m3/h, covers 20 m2
  • : 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  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.
  • 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.
Air Purifier Results — Office (21 m3)


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

Xiaomi, meet Blueair
Xiaomi, meet Blueair

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 , 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%.
  • 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.)
  • 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 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.
  • CORRECTION March 18: new data from the incredible  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)
Air Purifier Results — Bedroom (40 m3)

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 , 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  and  — 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 , ,  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, . 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.


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45 thoughts on “The Best Air Purifiers Under 1,000 RMB: My Test Results”

  1. I just found out that Xiaomi’s purifier looks extremely similar to a Japanese machine from company Balmuda, costs 7 times more:

  2. Thank you for all your information.

    Having read your previous article on your testing, I had finally decided that I would buy some Philips purifiers for our apartment. Philips 4012 for the bedrooms and a 4072 for the living room. But do you think they will be a bit small for our needs based on the CADR?

    Bedroom 1 18m2 and 50m3
    Bedroom 2 13m2 and 35m3
    Living room/dining/lounge 44m2 and 123m3

    I am now thinking that the Xiaomi machines would be more suitable and cheaper. I agree with your reservations about replacement filters/maintenance etc, but they seem such a good machine……..

    I am going to get 1 each for the bedrooms.

    For the Living room, do you think 2 Xiaomi purifiers would be okay or should I buy 1 larger (and more expensive) purifier that would do the job on its own?


    1. Don’t forget that last step of multiplying your room volume x 5 to assess if it matches CADR of a machine. So the CADR of the 4012 is pretty small even for the bedrooms. The 4072 of course is higher but for the cost, Xiaomi certainly is a good value. So the living room needs CADR of 615 m3/h and 2 Xiaomi machines, since each does 406 m3/h, should be adequate. Even 3 machines still isn’t even 3000 RMB total cost…

      1. JD and Tmall are both out of stock for the xiaomi machines. So I have registered with Xiaomi and will see if I get lucky on Tuesday noon. It seems you can only reserve one at a time so I will be trying Jd and Tmall on Tuesday as well.
        Being a little impatient I bought the Philips ac 4074 (2800rmb) and put it in my main bedroom. On auto it went from red to blue in about an hour and during automatic night mode it seems to have shut down. I’m assuming it thinks air is good.
        If I can buy 3 xiaomi machines next week they will only cost me slightly more than the 1 Philips

      2. Good luck with Xiaomi, you’re going to need it. they sell out ridiculously quickly…generally I’m not a fan of auto mode even on the expensive machines, I just don’t trust their built in sensors and would rather control up and down myself…

      3. Well, after 2/3 weeks of trying i was unable to buy the Xiaomi machine. Very frustrating.
        I have increased the sensitivity on the Philips, wow its a different story it even starts up with the smell of aftershave now.
        I have ended up buying a couple of Blueair 550E. They seem good, but I will be buying a particle counter just to check.

  3. Thank you for the detailed test. The result supports my original choice.
    However, I do not know how to get a Dylos DC1700 in China (Shenzhen). They only ship to the US and Canada. Do you know how to get one in China? Thanks!

    1. I know they are available on shopping websites like Amazon China or tmall but it’s quite a bit more expensive than in the USA. ..

    2. you can buy Chinese one for 400RMB on, this is 2nd bestselling

      and this one even cheaper is 4-5th bestselling for 300RMB

      and if you feel extremely adventurous search on for PM2.5检测仪 and you can find plenty PM2.5 meters from 99-150RMB

      1. Thanks Markoff
        I have just bought the 400RMB one from Amazon.
        Its going to be interesting to see the results for my apartment.

      2. Yes I and many others would love to see how accurate are those more inexpensive particle monitors. But the only way to really know if they work well is to compare side by side with a “standard” monitor…

  4. Thank you very much for this review!

    As many readers, I’m very interested to buy the Xiaomi, even if it’s a new product… My question is about the filer: where can we buy them? what is the average cost?

    Thank you very much,


    1. Their filter is here on their own website for 149 RMB — but apparently this is also hard to get and you need to reserve, which is very worrisome. You can also see many 小米滤芯 on Taobao — but I just don’t trust Taobao for anything anymore.

  5. You mention formaldehyde here in passing… do you have any data on indoor pollution due to VOCs? We’re here in Seoul where the PM pollution is often not as bad as in China. But during cold winters the house is sealed up and nearly everything inside from the flooring to furniture to cabinets is artificial. There’s an explosion of autoimmune disorders here that seems to have a lot to do with indoor air quality. My question is 1) is this a reasonable connection to make (also based on personal experience feeling unhealthy when the apartment is sealed) and 2) what purifiers do something about this problem.

    We already have a midrange HEPA filter that is probably doing something for particulates. It doesn’t seem to do anything about off gassing. Top line manufacturers like IQ advertize models that should make a difference. Do they? Do cheaper models as well?

    1. VOCs like formaldehyde, etc certainly can be an issue, which is what the carbon filters are usually for. Sure, if you can afford a great HEPA and a carbon filter, that’s probably better, but the carbon definitely slows down the air filtration rate (like the Blueair SmokeStop filters).

  6. So, I have a question about the Smart filters and VOC and other indoor air pollution concerns. I am convinced they are equal to other machines in terms of PM2.5 filtration, and of course their price is great, even if the looks are kind of rough. But I’ve not seen any data (unless I’m missing it?) on how they do with indoor pollution worries. That’s a huge issue here, which has come home to me as my upstairs neighbors do a complete remodel that has sent naseating and dizzying stench into my 90sqm apartment, which has two Alen air 375s and one Alan Paralda running in it. Even that much extra filtration (that much Alen should be good for 150sqm place) wasn’t able to keep it completely at bay, though it did clear out pretty quickly. People often ask me if the DIY smart ones aren’t good enough, and of course they’re better than nothing. When comparing PM numbers, yeah, they’re good enough. But what about these other concerns? Should we really be saying they’re “as good” or “comparable” to more expensive models if they can’t deal with formaldahyde or other VOCs? If anyone knows of data with these cheaper machines, especially the Smart ones, that deals with this issue I’d be grateful to know about it.

    1. The DIY guys at Smartair looked into this and designed a carbon filter for VOCs, here’s the data Bottom line, it works as all carbon would against VOCs — but most homes don’t need this nearly as much as a HEPA filter for PM2.5 and smaller…

  7. Thanks for all your posts.
    I read some of them and also the comments.
    I’m looking for a review of particles tester, as the Dylos 1700 you used. You mentioned an existing review but I can’t find it. Thanks.

  8. Thank you to share all information. I’ve just a question: what is the connection beetween a vaporizer and air pollution? I mean, I tried at home to use an humidifier and then I discovered that the level of PM 2.5 in my room was increased (using a particle monitor to calculate).

  9. Thank you for all this testing and publication, it is very informative.

    I have a general question about inside pollution: I think I recall reading somewhere on this blog that inside air quality, if you’re not using an air purifier, is the same as outside. Then what’s the use of the “stay indoor” recommendation? Just to reduce activity and therefore breathing?

    Also, I don’t go running if AQI is above 50 (US), meaning I haven’t been for two weeks here in Shanghai. I very much dislike running on a treadmill but I was thinking about going to a gym anyway. Now if inside air is as bad as outside that doesn’t seem like a good alternative. Maybe some do but I have never heard of a fitness club advertising purified air.

    1. thanks for the comments; yes in general, outside air pollution diffuses into homes so indoor air PM2.5 is relative to outdoor air, maybe 50-80% in my experience. So of course it’s only helpful to stay indoors if you’re using air purifiers inside to really make a difference. Regarding gyms, i’ve heard many differing stories ranging from windows and doors open (bad idea) to having air purifiers installed (great idea). As far as running outside, your cutoff of 50 is a bit extreme, why not wear an n95 mask when running? even on slightly polluted days, running outside is still far better for your health than no running at all.

      1. I was using 50 because where I come from (Switzerland) that’s when they start to take measures like broadcasting warnings and reducing speed on the freeways. And when running one breathes how many times more than when resting? 10 times? That would then be like an AQI of 500. But I agree that this might be extreme and I’ll use 100 as a new cutoff and see if it doesn’t burn too much.

        I gave up trying to wear a balaclava when cycling in cold weather after 2 minutes because condensation was a problem. I was thinking running with a mask would be the same and make it hard to breath. I’ll have to give it a try though (and generally wear a mask which I never do, I’m new to this environment.)

        Thank you very much for your comments and recommendations.

  10. your finding was referred at his blog:

    “ a day in Beijing is like smoking one sixth of a cigarette. More specifically, on an average day in

    Beijing an average adult inhales a total of 1.8mg of PM2.5 particles from air pollution, which is 1/6 of the average 12mg of PM2.5 particles inhaled from an average cigarette”

    I am curious about the source of 12mg PM2.5 from average cigarette. Is 12mg the total amount of PM2.5 by burning of a cigarette? Or only the amount inhaled by the smoker, which must be a very small percentage since majority of the smoke(PM2.5) would likely be difused to the air? Could you please give the source or more details about the calcuation?

    Really I feel articles like the above blog could mislead the innocent people.

    Thanks a lot!

      1. Thanks a lot for your reply. I noticed your early article, but could you please give the exact reference for Dr. Pope’s article: journal name, year, volume, page. I really like to find out how the number (12mg for a cigarette) come out. Thanks again

  11. I tried some online search, and it seems 12mg was meant for “12mg nicotine”, not 12mg PM2.5!!!

    Below is one of relevant links.

    “Strength: medium (12mg nicotine) and strong (18mg nicotine)”

    As a PhD chemist, I am very sure that nicotine is only a very tiny percentage of all chemicals in the smoke from burning a cigarette. So I would suggest you get this clarified. Otherwise, the original statement has really been misleading.


  12. Dr. Saint Cyr,

    We have purchased a Xiaomi to place in our son’s kindergarden. A few questions:

    1) What English language Xiaomi fan/discussion groups are you aware of?

    2) What does the air quality in the app equate to?

    3) How does the outside air quality number relate to the numbers?


    1. I’m not aware of any Xiaomi fan pages — this page here is probably the first! Xiaomi has their own bulletin boards, but it’s all in Chinese. Their built-in sensor measures PM2.5 concentration (ug/m3) not AQI; in general under 12 is the best (means AQI under 50) — but their sensor isn’t so super accurate, in my opinion. Their other data on the lower part is the PM2.5 concentration for outer air as measured hourly by the governmental machines — usually the closest monitoring tower to your home.

    2. Hi Steve,

      Did you buy direct with xiaomi or resellers?

      Did you notice if there were any filters for sale?


      1. I bought from resellers, it was impossible on their own site. And they now have filters for sale on their own website , I just got 2 and delivered overnight no problem。

  13. First of all, thank you for the great info :).

    Would like to ask you for some opinions.

    I am now contemplating between a new Xiaomi or a barely used Philips AC4072 (roughly the same price as Xiaomi).

    My bedroom is 4.42m (length) x 2.6m (width) x 3.36m (height) = about 39 m3.

    Following your calculations, the total CADR that i would need is 39 x 5 = 195 CADR.

    While the Xiaomi’s rated CADR (406 m3/h) reduced in half (203 m3/h) would be suitable, the Philips’ rated CADR (309 m3/h) when reduced in half (155 m3/h) is short of my requirement.

    Which one do you think i should go for?

    Besides, do you have any recommendation for good humidifier available for purchase in China? I am regularly in an AC room so would need a good humidifier to prevent dry throat.

    Thanks in advance.


    1. That’s a tough one but I really like the reputation of Philips so that’s a really good deal. I tested them last year and it was a solid model, easy to get refills online, has separate prefilter and carbon filter…

      1. Thanks for the swift reply Dr. :).

        Do you happen to use any humidifier or have any recommendation for a humidifier?


      2. I think any ultrasonic humidifier is pretty good. I’ve used some from Westinghouse, I got them on Amazon China website, not bad at all…

  14. Great article. Very informative. Thank you Dr. Saint Cyr.

    I read that air purifiers with ionizers (like Blueair 503) create and fill the room with potentially harmful levels of ozone. (Here are a 2 links to info written by Consumer Reports on this topic & )

    Should I avoid Blueair 503 and do any of the units reviewed in this article have an ionizer?

    1. Perhaps an expert can handle this in another comment, but from what I understand the Blueair is not an ionizer, it does something to charge but it creates no ozone and they’ve shown data to prove this on their website and which others have mentioned are OK, and as far as I know it’s not on any list of dangerous ionizers. You mention this California article but in fact Blueair is in their list of safe air purifiers Consumer Reports also usually ranks Blueair super high and they don’t rank ionizers… but having said that, I’ve talked to a few experts who always mention concerns that Blueair still leaves “sticky” charged particles all over the room and furniture. Honestly I’m not sure what to make of that or of any data to support that concern as a real health issue.

    2. given the lack of objective data in the air purifier industry, and the lack of integrity (they lie and mislead), i am finding it impossible to make a choice.

      i wonder if anybody has ever tested the airpura r600? it seems to have the best specs. perhaps eveybody with a particle counter can contribute to a website with their readings for various air purifiers and box fan filters.

      the other question is long-term filter replacement costs. we’d need objective data on that too, or at least data on the specific hepa filters.

    3. Is is safe to say that the more carbon in an air purifier, the better the VOC filtration (ignoring fan speed)? If you can, please test the airpurifiers you own (with OEM filters) to see what impact they have on VOCs? Thanks!


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