Air Pollution, Air Purifier Reviews, Children, China public health, Hall of Fame, Indoor Air Pollution

Air Purifiers For The Other 99% — How About Philips?

36 Comments

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.

 

I’ve blogged a lot about testing my air purifiers at home, a quartet of machines (three IQAirs and one Blueair) working in symphonic harmony to create indoor air 80% cleaner than the outside air pollution — 24 hours a day, every day. I find this 80% to be very reassuring, especially for my newborn son, who will be spending almost 100% of the first years of his life inside our home. Air purifiers in China are a no-brainer, must-have item! I would be even more cheerful if one more criteria could be improved — the cost.

Each time I pay for replacement filters, I get really ticked off that I’m paying so much money — and so much more than I would than if I lived in the USA or Europe, ordering exactly the same filter. It’s simply infuriating that a replacement filter in China could cost more than an entirely new machine in America! In the respected Consumer Reports list of top air purifiers, the highest rated machine is only 2,118 RMB (~350 USD,  the Whirlpool APS 1030K). Even the Chinese press has started to cover the extortionate prices of some air purifiers, especially the replacement filters.

I actually feel partly responsible for this, as many thousands of readers have bought machines based on my recommendations. Here in our expat bubble world, sheltered underneath our shiny pollution domes, we all keep self-promoting the same heavily advertised imported brands, creating a self-reinforcing illusion of brand superiority. Meanwhile, the other 99% of people in China couldn’t possibly afford almost any machine I’ve recommended. So while I appreciate my current machines, and while they truly are highly rated from many independent sources, they are far from the only viable options out there — and definitely not the best value for anyone with limited income.

I can’t say I’ve found the perfect solution quite yet — perhaps the team at Smart Air Filters could help fill that gap — but I may have finally found a decent value. It’s the Philips range of air purifiers, especially the AC4072, which I recently gave to my in-laws as a Christmas gift (only in China would that be a hot gift!). I chose this because it ranked very well on the test results last year from the Shanghai Consumer Rights Protection Commission, where its sister model, the Philips AC4074, filtered 96% of PM2.5 and 53% of formaldehyde — using the same HEPA filter as the cheaper AC4072. Plus, my new comrade-in-arms in geeky air pollution testing, Thomas Talhelm, recently published his own data comparing his DIY filters against this Philips as well as the Blueair 203 — and the Philips was as good or better than the Blueair, eliminating 93-96% of PM0.5-2.5 on high speed overnight in a small bedroom. Thomas and I are on similar missions to share data with the world, and he’s even more focused on finding value — a very important and noble goal. The AC4072 is currently 2,900 RMB direct from Amazon China, compared to my Blueair 503’s price of 5300 RMB, my IQAir Pro 150 price of 9,000 RMB and my Pro 250 price of 11-15,000 RMB (depending on voltage and import status). 

For my own tests, I did my usual routine: I compared real-world situations, not just blasting them on high speed all night, which I feel is an impractical and loud scenario that no one does in real life. In real life, we want the most effective machine at a reasonably quiet level. I want to know:

  • How much better is the air when I’m sleeping?
  • How much better is the air in my big living room, and the rest of my house, during the day?

I always compare my indoor pollution to the outside air at that time, because again my most crucial question is “how much better is my air inside, compared to outdoor air?” As I mentioned before, my current system is 80% better. Can the cheaper and smaller Philips keep up the same good results as these famous flagship models?

Envelope, Please…

I was very pleased with the results. In my 13 square meter bedroom, overnight with the doors closed, the Philips AC4072 on a lower setting filtered out 87% of PM1 and 98% of PM5, when compared to the outside air. I usually have the Blueair there, and while the AC4072 wasn’t as wonderfully quiet, it was very reasonable white noise and still performed at least as well as Blueair and others in previous tests. During my last testing of Blueair, IQAir and Airgle in my bedroom, their combined effectiveness overnight was 90%, so the Philips data is right in line with that.

In my 30 square meter  living room, it filtered 84% of PM1 and 96% of PM5, again compared to the air right outside my window. These numbers are very comparable to previous data, which again is impressive given the clearly smaller size and price. In last summer’s test, the living room average was 85%, so yet again the Philips is exactly in line with that data.

My Bottom Line

Despite the clearly smaller HEPA filters and unit size, the Philips AC4072 performed equally as well as all other units I’ve previously tested. Plus, it was generally quiet at most settings, and their automatic mode was quite useful for the front room. And it doesn’t hurt to be a bit sleek and stylish, occupying less than half the floor space of my other units. Regarding value, it’s half to a third the price of my current machines (same goes for the filter replacements).

That’s good news for me, and for the tens of millions of others across China who are looking for quality performance with value for money. Even this AC4072 is probably overkill in smaller bedrooms, and maybe their cheaper AC4025 or AC4012 would be fine. Besides Philips, I’m sure that quite a few models from the other major brands also would be just fine, many with prices far below the famous foreign brands. Daikin, Sharp, Panasonic, Whirlpool, Westinghouse, Honeywell, Yadu … as the DIY folks are starting to prove, all you really need is a good HEPA filter and a good fan. 

UPDATE 2024: Please follow me at my new website, DrSaintCyr.com. Also my new YouTube channel youtube.com/@drsaintcyr

36 thoughts on “Air Purifiers For The Other 99% — How About Philips?”

  1. Good to see the good results from Philips.

    I’ve been extolling the value of Yadu air purifiers for a few years here, IMHO they are worth considering with their low replacement filter cost, though I haven’t performed any testing to demonstrate their effectiveness.

    1. Yes, I would love to borrow a Yadu sometime and test it out! Or others can also test their own machines, since the Dylos particle monitor and others are quite inexpensive. Since there’s no comparable version of Consumer Reports here in China, we consumers need to do our own research!

      1. I just ordered a Yadu KJF1353E for my office this morning as I have been quite bothered by the pollution recently, the cost was only 849 RMB and it should arrive this afternoon (gotta love Jingdong).

        It has 3-stage filtering (prefilter, activated carbon, HEPA) so it should be effective against particulates as well as VOCs in a small-medium sized room.

        Anyways, I’d be happy to lend you mine if you’re interested in testing it out.

      2. Interesting — as usual, it would be great to see independent tests. Let us know what you think! I assume this is for a small room?

      3. I’m all for more independent tests. The problem is that I currently do not own a particle counter (though I do intend to get one).

        This will be mainly for my office (at work), though once the pollution gets better I may take it home for use in the guestroom. This unit is rated by the manufacturer for use in a 30-40 sq m room but as you know these ratings tend to be exaggerated (15-20 sq m is probably more realistic).

      4. Well the Yadu arrived this afternoon as promised. It’s a good value for the money – the filters appear to be of decent quality and there are some features that you don’t usually find in this price range such as air quality indicator (3 levels) and remote control.

        However, it is louder than I expected. While the two larger Yadu units I have at home just make a rushing wind noise at higher settings, this one also makes a whirring noise which is harder to block out (mentally). Using an SPL app on my iPhone I measured 55dB on medium and 57dB on the high setting from a distance of 1 meter. On low setting it is very quiet and below the ambient noise level of my office (42dB). However, there isn’t much airflow on low. I wish there was a setting between low and medium – the added airflow without the noise of the medium setting would be perfect.

        Perhaps it is overkill to use the medium setting in my small office? For now I’ll probably just keep it running all the time on low and switch to medium on “bad air” days.

  2. Thank you Richard,
    it’s great to see that you take comments into account for future posts.
    It’s true, many of us, including expats not just Chinese, cannot afford those expensive purifiers and others are here for a limited time so a budget purifier makes more sense than those overpriced machines.

    1. In addition to Yadu, there are air purifiers available from other smaller (and cheaper) local brands that also appear to offer decent filtering capability. The reason I went with Yadu this time again is because I don’t want to worry about those other companies going out of business (or getting out of the air purifier business) and thus not being able to source replacement filters.

  3. Dr Saint Cyr,

    Thanks for this review. We have been using 3 of the Philips AC4085 with is the 55m^2 version that combines humidifier. I really like the automatic nature of the machines so that they are usually on quite mode and when the pollution rises, or the mother in law is cooking, they crack it up to clean the air.

    We also bought one to put in our sons kindergarden.

    1. I agree, that automatic feature isn’t even on my current Blueair or IQair, and it did seem to work well on my Philips… many sensors aren’t accurate but this seemed appropriate.

  4. Hi Dr Stain cyr,
    Thank you for your post. In china, We have 2 Philips AC4072 ( look like the one on your pic with post) and 2 alen air.

    My 4 year old has have a chronic night cough and has just been diagnose with asthma here in Germany. ( only symptom is cough).

    We will I was wondering if we should invest in a IQ air for him when we move back next month. Do you have any thoughts on this?

    I told my husband that the extra bit he makes in china are all going to buying and maintaining air filters in china And the kids international school. We are also put our health out there too. I guess that’s why so many family choose to leave.

    Thank you and I love your posts.

    1. Thanks for liking my posts, Kelly. Regarding “investing in an IQAir”, that implies that you think that’s the best machine out there, even though you already have 2 Philips and 2 Alen. I own 3 IQairs, but I haven’t seen any credible research that their machine would be any healthier for you than any other good HEPA filter. They of course do claim that their newer filters get down to PM0.003, but again have they proven that other machines don’t do that? And have they proven improved health effects with the lower filtration? If they are considered the “gold standard” of air purifiers, then why haven’t I seen one published journal article on air purifiers and health that uses IQAir? I’m researching this right now, for an upcoming article, and I’ve found half a dozen projects, which used an assortment of purifiers — but none used IQAir. So those researchers didn’t consider IQAir the obvious choice in their projects. Plus, in all of my testings over the years, my results never showed that IQAir had any clearly superior real world effectiveness better than any of the other machines I tested.

  5. While a press release is not a peer reviewed article, the Hong Kong Health Authority (HKHA) did have IQAir come out on top as its pick for providing protection against viruses (SARS in particular) back in 2003. Viruses are very small, much smaller than PM2.5 as they can be as tiny as PM0.005. At least to the satisfaction of the HKHA we have evidence of the superior performance of an IQAir over its rivals.

    That said, the vast majority of people in China buy an air purifier to reduce exposure to PM2.5, not viruses. Certainly being protected from a virus is a good thing, but it is not the main driver. Is it worth the difference? I think that is the reason you are reading this thread! For people with chronic health issues, I think its an important factor they should consider, even in the absence of studies showing clinical benefits of ultra-fine filtration. All would do well to stay informed and try to make the best choice they based on their own situation.

    In the interest of disclosure, I do sell these kinds of machines, so I do have an interest in trying to associate the superior capabilities to remove ultra-fine particles with health benefits.

    Here is the link to the press release:

    http://www.iqair.com/newsroom/2003/iqair-selected-to-provide-hong-kong-hospitals-with-new-tool-for-fight-against-sars

    1. Thanks, David. I’m sure we will be reading more and more about ultra-fine particles as research comes in.

  6. I’d like to get comments to following findings.
    I live in house with centralized air heating. Air is heated by water/air heat exchanger and heat is produced by gas boilers.
    Air intakes (2) are in hall close to living room.There are originally steel screen filters and I have added approx 5mm thick filter fabrik (IECxxxx G3 from Europe) on the top of screens (50x60cm). IQAir 250Pro (6 months old) cleans air in less than 5 meters from heating air inlets. I’m wondering following: Filters in heating inlets collect visible dust (very fine grey powder etc) so much that they blocked within a week. I have vacuum cleaned filters (Electrolux allergy dust bag + hepa), colour change from grey to almost white and re-used filters. No dust are on any shelfs or side tables in the room. IQAir prefilter is not blocked and air comes still out. Why G3 filters collect so much more dust than IQAir? Just due to larger air volume?
    Sometimes I experience visible dust (not particles but just kind of “grey air” ) in room when watch thru the air against bright sunshine. Can the particles be so small that they go though IQAir filter? I live outside Beijing downtown in Shunyi and car roof becomes dusty within 1-2 days after wash although PM2.5 is 50-70.
    I spent 15 eur (130 rmb) to 200x140cm piece of filter fabrik. My “filter machine” is not noisy at all.

    1. That is a good question. Could you clarify what you mean by intake and outtake? I want to make sure we are on the same page.

      For HVAC, I prefer to use the terms “supply” and “return” Supply brings the conditioned air (heated in the winter, cooled in the summer) into your living space and the Return takes the air out of your living space.

      What is the verticle height of your air supplies and returns? Are they different? In the walls or the ceiling? How far apart are they from each other? How many returns and supplies do you have?

      If intake means supply, your G3 fabric filter (MERV 5 in North America) might be doing just what it is should, filtering out the coarse particles before you (and your IQAir) have a chance to inhale it. Your PreMax filter is rated F8 (MERV 14/15) and HyperHEPA is rated H12/H13 (exceeds MERV 16). Sorry for the alphabet soup, but the point is your filter fabric is for coarse particles, your PreMax is for fine particles, and your HyperHEPA is for ultra-fine particles.

      You are right, a lot more air is moved by your HVAC system than what your IQAir. The other thing I am thinking about is you might have a “short circuit” in your air flow. If so, air is moving from your supply to your return before enough has mixed within you living space to reach you and the base of your IQAir where the pre filter is It is not that uncommon for HVAC systems to have design faults with this or for some alteration (such as a new interior wall) to cause this cause short circuiting down the road. Supplies and and returns in or near ceilings can be more susceptible to this. Checking to see if you have short circuiting or if your HVAC system is out of “balance” (air from supply matches air to return) is beyond the scope of what I do, but should be something a HVAC technician (or even your building maintenance staff) could do and maybe make some adjustments. Of course, if I got your meaning of air intake right, they might be working as designed.

      Let me know if I guess right what you meant by intake and outtake. If I got it wrong, then something does seem really wrong. I’d to try to do some research what that might be.

  7. Hi David and thanks for detailed information. My native language is not English and I may use a bit strange wordings.
    The HVAC is following, I called Return earlier as “intake”. There are two 50x60cm (20x25inch) openings for return with steel screens on wall, v. height of 200cm from floor. Air goes in and my G3 is pre-filtering at that point. Heat exchanger is somewhere inside ceiling. “Left” opening is for 2nd floor and the “right” opening is for 1st floor. Air distribution i.e. supply is in several places around the house. Each three bedrooms on 2nd floor have supply thru openings on floor. So we have air circulation from bedrooms on upstairs down to return opening in 1st floor hall. Bedrooms have small Electrolux hepa filters.
    Supply on 1st floor rooms is on the wall close to the roof except one supply on the floor on living room close to the hall. Short circuit from living room floor supply and return is possible. Living room is very high, ca. 6 meters (20 ft). IQAir is on opposite wall from return openings (5 meters distance) with one supply on the wall above IQAir in living room.
    The HVAC described above is a closed circulation. Air is not blown out nor fresh (well, Beijing outside air) air is taken in. Similar to car A/C which you can choose air circulation only in heavily polluted neighbourhood, without outside air blown in. Bathrooms (3) and kitchen have separate forced (electrical) ventilation which blow air out from house. No actual supply for this, house is “leaking”.
    G3 filtering is much easier to arrange in return than in supply points. Two return openings only vs more than ten supplies plus vacuum in return screens makes it very tight.
    I hope I was able to explain this at least a bit more understandable way. I know that G3 is a coarse type, purpose is just filter visible dust away, clean air a bit and reduce need for cleaning. We have an ayi, a domestic help that vacuum cleans house daily.

  8. Hi Jorma,

    Thank you for clarifying on the supplies and returns and other details.

    Perhaps your downstairs living space might be a bit too much for a single IQAir. Before you buy another purifier or replacing your ductwork, I think it makes sense to try to figure out what is going on first. Visual inspection of a filter (especially a fine particle filter like a PreMax) is not a particularly informative, but it does seem strange that it is viably clear while your G3 filter fabric gets clogged. Maybe your air returns are downwind of a furry friend’s grooming spot or a shaggy carpet. IQAir and third parties make a coarse particle filter, but the PF40 kit and replacement pads to my knowledge are not sold by IQAir China’s authorized distribution channels. I do offer them on special order.

    I do understand that it can be difficult to put your G3 filter fabric on your air supplies. Convenient preventative maintenance is not always a design consideration with HVAC systems.

    While I don’t have the equipment or expertise to do make a proper test any air flow short circuiting or check the balance of your HVAC system, I might be able to do a rudimentary test. Before I return from America after Spring Festival, I’ll ask an experienced HVAC contactor I know if he has any ideas about what is going on. I’ll also asks our contract HEPA filter maker in America as well, as they are well acquainted with IQAir’s filters.

    I think it is worthwhile to check the PM2.5 AQI in your home as well as confirm the HEPA efficiency of your IQAir. HEPAchina offers a free IAQ awareness assessment within the forth ring road that can at confirm how much lower your PM 2.5 levels are inside compared to outside air. We are also able to see if your IQAir (or any HEPA purifier) is meeting the HEPA standard. While you might want a more extensive assessment of your indoor air than what we offer for free, I suspect that something else is the major cause of the accumulation on your G3 filter fabric. Alas, our particle counter is still in America for its annual calibration, so we won’t be able to do our free PM2.5 check until after Spring Festival. If nothing else, the free assessment should demonstrate that your inside air is cleaner than outside and your HEPA purifiers are working. A bit of peace of mind to put you at easy while mystery of your clogged G3 filter fabric still evades us.

    In the meantime, it could not hurt for you to diary the relative amount of accumulation on your G3 filter fabric when the outdoor PM10 and PM2.5 is elevated. A knowledgeable HVAC engineer might be able to makes some sense of it.

    I think we have reached the boundary of what is relevant to the topic of this thread. I’d be happy to talk with you further privately if you can contact me through HEPAChina.com. We can’t solve all mysteries, but I think it be useful to see what is going on, and should our host have a another post where this discussion would be more germane, share anything useful uncover.

    Sincerely,

    David Helman
    HEPAChina, Director

  9. Hello People,

    I recently stumbled onto this nice doctor’s website by accidentally stumbling onto the aciqn.org website first. I really love reading about his articles. I’m originally from NYC, born and raised; but circumstances happened in 2008 and now I’m living in Hong Kong with my family that’s originally from this city and Shanghai.

    I travel into China all the time and have noticed that even though the air pollution in the mainland is bad, it isn’t however as bad as how it feels in Hong Kong. (Haven’t been to Beijing since 1991. Can’t compare yet.) The humidity, overall warm to excruciating temperatures from May to October is a killer in terms of enjoying the outdoors. During the cooler months from November to April; the polluted air is bearable; but still disgusting. There’s a constant haze in the skyline and very often the smog would be so heavy; we couldn’t see farther than 300 feet. The smog would seem like heavy fog. I’m lucky to live on a small mountaintop around 350 feet in altitude with no surrounding buildings blocking us.

    Because of being used the ther overall blue skies and white clouds in NYC, I’ve resorted to buying three air purifiers. One for the living/dining room, room for master bedroom, one for another bedroom. I have yet to buy a fourth one for our walk-in closet/guestroom. (Even though NYC it’s considered a polluted city in the U.S.)

    Does anyone have any experience with these air purifiers:

    1. Philips AC4004 (living/dining room)
    2. IONcare GH2173 (master bedroom)
    3. LuvA SAP-XG (bedroom)

    I’m thinking of trying to find a better affordable air purifier in case these die and for the fourth room.

    Happy New Year!

  10. Thanks for this useful guide. I’m considering the AC4012 model. Would like to check of you have any idea on the class of the Hepa filter it uses? I tried to check their manual and specifications but to no avail. How often do we need to change the filter on philips purifier? Thanks much in advance for your kind advice.

    1. I don’t think so, but you’d have to check their official website for details

  12. I’ve got a couple of Sharp Air Purifiers, they have that plasma thingie that can clean air in the room even if it doesn’t pass through the machine — it works *extremely* well. I use it only when we leave the room, though, it claims to be ozone-less but not completely confident.

    However the one aspect I am not satisfied with is the automated mode. The machines are VERY sensitive to smells and would go on full blast to the slightest of odors but would stay happy green even if put outside at 150 to 200 AQI (at the highest sensitivity setting).

    It would be really helpful if auto modes could be tested as well… higher settings are not practical at night as they are simply too noisy.

    Other than that I recommend looking at the official china site for sharp to read the various specifications for the different models. As a rule of thumb I’d cut in half the room size that they recommend, e.g. if the room is 20sqm, get a machine that can handle at least 40sqm if you intend to use the auto mode, as the auto mode or lower setting on the weaker machines which supposedly can handle 20sqm is completely useless. You’d hardly be able to notice air flow even if you keep the windows open when it’s 200 outside.

    The filters on the Sharp machines are supposedly usable for 5 to 10 years unless they start to stink. When calculating costs the filters costs have to be included. I doubt if the filters on the really cheap machines can last for long. Then again, I doubt a filter can be used for 10 years without absorbing various odors but what do I know.

    BTW here is a category for new articles on this site: on taobao there are now many products to self test contamination on food and products such as lead, there are also cheap gadgets to check if your “pure water” is in fact pure or to check for formaldehyde in the room for a few RMBs.

    I’ve been using the water gadget which cost me 200 RMB (there are different qualities) and it seems to be quite accurate and good enough so I know if the water I’m buying is fake or not. As for the food contamination testing, I’m regretting testing as there is no way for me to start buying all imported food.

  13. which is difference ac4072/00 and ac4072/11 ?
    but this ac4072 is same rowenta pu2120 or ac4012 is the pu2120?
    you know also z9124 electrolux?

  14. I think I figured out why the Sharp AIr Purifiers automatic mode is completely useless and stays completely “green” even at 150 or 200. The reason is that it probably uses the local Chinese AQI calculation method (AQI = MAX{of all individual IAQI which is a specific Chinese calculation method…). So, the question is, for BlueAir and IQAir does anyone knows if they have their automatic setting according to Chinese standard based on the IAQI or the international standard for AQI? Thanks.

  16. Basically says that life expectancy is very low for people in Beijing but is coming more in line with developed countries. Also will go up further as average income goes up and technology improves.

    I guess the scary part is about how the end portion of one’s life will involve a lot of pain and sickness.

    The main recommendation of the article is to improve your phsyical/cardio fitness (yundong nengli) as this is the most significant of the eight factors looked at by the WHO study.

  17. Dr. Saint Cyr,

    I read with interest your posts about 3M masks. I bought a 5 pack of “9501”‘ masks from Decathlon for 30 yuan a few days ago. While shopping the 3M taobao store for the 9001V masks for biking, I also saw that they sell a few air purifiers. There is one, the KJEA400, which seems comparable to the Alen Air A375, it’s 3680RMB on amazon.cn. But a U.S. based allergy/air-purifier website says this about 3M’s Filtrete filters:

    “Another potential drawback is that the filters are not HEPA. The filter is made of a charged media that initially outperforms traditional HEPA filters. Being charged, the trade-off of this is that these filters tend to clog more rapidly than HEPA filters.”

    from: http://www.achooallergy.com/filtrete-clean-air-purifier.asp

    This same website also uses this terminology to describe 3M’s filters: “High-performance, electrostatic filter captures 99.9% all airborne particles 0.1 microns or larger better than HEPA.”

    So my question is: What is your take on this “better than HEPA” concept? Why would 3M’s popular Filtrete filters not be HEPA filters? SmartAir sells their HEPA filters for $13, so surely you couldn’t make the argument that 3M is saving money by not making their filters true HEPA filters. Also consider…

    This website (www.achooallergy.com) also points out that Alen Air’s T500 filter also uses “HEPA-type” filters. A look at Alen Air’s website shows this same wording (HEPA-type), clearly worded to avoid claiming to have a true HEPA filter. This is the comment that achooallergy representatives say about the T500:

    “My biggest issue with the Alen T500 air purifier is the lack of a true HEPA filter. The HEPA style filter of this model provides the equivalent of N95 filtration (95% of particles 0.3 microns or larger). This standard meets the CDC recommendation for preventing the spread of things like the flu, and it also provides enough filtration for light to moderate allergy and asthma sufferers. No matter how well this type of filtration works, it doesn’t change the fact that the industry as a whole, uses HEPA as the benchmark.”

    from: http://www.achooallergy.com/alen-t500-air-purifier.asp

    Most people (including you if I remember correctly) emphasize the importance of a HEPA filter. So would you recommend staying away from 3M’s Filtrete products? and the Alen Air’s T500?

    What’s your take on 3M’s “better than HEPA” claim?

    Alen Air’s Paralda and A375 do come with true HEPA filters.

    Thanks so much for your suggestions!

    1. The Filtrete has a great reputation on ConsumerSearch.com so I’m not sure what the complaints are. I don’t love the electrostatic angle but Blueair does this a bit and I have a Blueair. In general I personally would stick only with true HEPA filters for China. 95% just isn’t 99.9, and you’d really need a good fan or circulation to make up for that loss of filtration. It can be done for sure, but I’d stick with pure HEPA.

    2. One of the great attributes of a HEPA filter is that they don’t release particles. A “HEPA style” filter that charges particles can release particles over time, especially once its media is coated with particles, the charged particles are less likely to be attach to the media, and will “download” back into the air.

      When HEPA filters become saturated with particles, their efficiency should remain at 99.97 @ 0.3 microns, but their effectiveness will start to go diminish as less and less air can pass through the filter. This is why you need to change HEPA filters once its airflow has been materially reduced. On better HEPA air purifiers, the filters can last for several years before needing to be changed, even in Beijing.

      Something else to note, while the HEPA filter might be 99.97% efficient, the total system efficiency of an air purifier can be less, as some machines allow a lot of air to bypass the HEPA filter. HEPA filters are really tough for air to pass through (which in part explains how they are able to rated at 99.97%), so if the air can find a way to flow around the filter, it will. On some poorly designed and/or manufactured machines, a great deal of air gets bypassed.

      Blueair’s marketing says that unlike “traditional” HEPA, its “HEPASilent” (in other words, not HEPA media) is not prone to clog and will provide maximum airflow. Think about that, is the particles are not “clogging” the filter, where are the particles going? Back into the air once the charge wares off!

      David Helman, CRIE
      HEPAChina
      Indoor Air Quality Association Member

  18. Sorry, the reason I posted in this thread is that it was a continuation of the thought that there are other affordable air purifiers out there, not just the “Cadillac” models:

    Air Purifiers For The Other 99% — How About Philips? – or How About 3M’s KJEA400?

  19. Dr Saint Cyr,

    Wanna to say, that life expectancy in Beijing is very low for people but is coming more in line with developed countries. Also will go up further as average income goes up and technology improves.
    I’ve been extolling the value of Winix air purifiers for a few years but they are worth considering with their low replacement filter cost, though I haven’t performed any testing to demonstrate their effectiveness.

    Thanks
    John M. Turner

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