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2 Reasons to Avoid Most Electronic Air Cleaners

Electronic Air Cleaner

The pandemic has brought a huge amount of attention to indoor air quality, even without full acceptance of the aerosol transmission of COVID-19.  Unfortunately, it has also brought a huge amount of money to companies selling questionable electronic “air cleaners.”  And that in turn has brought a huge amount of pushback from the IAQ research community.

Last week I spoke with Dr. Marwa Zaatari, a mechanical engineer and IAQ consultant who is on ASHRAE’s Epidemic Task Force, and she gave me the lowdown on electronic air cleaners.  She’s been immersed in this field for about six years and has been one of the most vocal opponents of electronic air cleaners, especially those that use ionization.  Before we get into her take on the subject, though, let’s define what we’re talking about here.

Indoor air pollutant types

We can divide the bad stuff in your indoor air into two categories:  particles and gases.  Particles come in a wide range of sizes and come from different sources.  Larger particles are 100 microns or so in size.  They include the things you can see floating around in the air when the lighting conditions are right as well as things that are not quite visible to the naked eye.  A lot of these settle out of the air because of their weight.

Once we get down to 10 microns and less, the particles not only float in the air longer but also can penetrate deeper into your body.  Larger particles don’t make it past the upper respiratory system.  Smaller particles, especially those that are 2.5 microns and smaller (PM2.5), can make it deep into your lungs and from there into the blood stream.  These particles are one of the worst indoor air pollutants.  Some of them also carry viruses and bacteria that spread disease.


Gases are individual atoms or molecules that are on the order of 0.0001 microns.  There are a whole lot of gases that can be pollutants in your indoor air.  Some of the most common ones found indoors are nitrogen dioxide, ozone, carbon monoxide, and radon, although there are many other potential indoor air pollutants in the gaseous form.

The world of air cleaners

As with pollutants, we can divide air cleaners into two categories:  mechanical and electronic.  Mechanical air cleaners may use electricity to move the air, but the cleaning action is purely mechanical.  Basically, it’s filtration.  Air moves through a filter and pollutants traveling along with the air are captured through one of several mechanical processes (straining, inertial impaction…).  The better the filter, the more pollutants are captured.  Filters are great at capturing particles but standard filters let the smaller gases pass through freely.  To filter out gases, you need activated carbon or chemisorbent filters.

Electronic air cleaners operate on a variety of principles and come with an even greater variety of names.  The main ones are:

I wrote about ultraviolet air cleaners last year and concluded by saying:

Ultraviolet irradiation can help with your indoor air quality at home, but probably not as much as you were told by the person selling you the UV lamps.

It’s a proven technology and is used effectively in health care and other settings where the systems are properly engineered.  For home use, it’s a bit of a crap shoot.

Electrostatic precipitators are a type of electronic air cleaner that also may be OK.  They use high voltage to charge particles passing through the air cleaner.  Then those charged particles are collected on an oppositely charged plate inside the air cleaner.  They don’t release the particles into the room air.

The other types are what can be called additive air cleaners.  They add something to the air (ions, ozone, oxidizers…) and it’s supposed to remove the unwanted pollutants.

What the US EPA says

The first thing to know about air cleaning technology is that ozone is a lung irritant.  It should never be added intentionally or as a by-product of an air cleaner.  The EPA says this about ozone:

When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.

Here’s what I wrote about ozone generators in my article on ultraviolet air cleaners:

You don’t want ozone in the air in your home.  Yes, some companies do sell ozone generators and make claims about how the ozone will react with the indoor air pollutants and neutralize or destroy them.  Those claims are not supported by scientific data.  The EPA page on ozone generators shows what really happens.

The EPA also has an excellent document titled Residential Air Cleaners: A Technical Summary, which you can download from their website.  They discuss mechanical and electronic air cleaners in great detail, giving the pros and cons of each.  Here’s Table 1 from the document:

Table 1 from the US EPA's Residential Air Cleaners, A Technical Summary

Table 1 from the US EPA's Residential Air Cleaners, A Technical Summary

The document above is addressed to the residential market, but the technology is the same whether you put it in a home, school, or coffee shop.

The 2 reasons to avoid most electronic air cleaners

When I spoke with Marwa Zaatari, she told me that the results being promised by companies selling most types of electronic air cleaners are overblown.  Independent researchers haven’t been able to reproduce the high effectiveness rates claimed by the manufacturers.  Here’s a Twitter thread she posted about the research into needlepoint bipolar ionization.  She examined three claims:  reduced particle counts, deactivation of the SARS-COV-2 virus, and the removal of formaldehyde and volatile organic compounds.  She found that what manufacturers are claiming is either false or can’t be verified by independent researchers.

So, reason number one is that a lot of electronic air cleaners just don’t do what they say they’ll do.  There aren’t really any standards or regulations they have to follow.  They can pretty much devise their own tests of effectiveness, keep the test methods to themselves, and claim whatever they want.  Jim Rosenthal illustrated this problem brilliantly with a spoof article claiming 93% effectiveness in reducing viruses, mold, and bacteria with a simple incandescent lamp.

The second reason to avoid most electronic air cleaners is that they may actually be bad for indoor air quality.  I’ve already established that ozone is bad for indoor air.  Many electronic air cleaners release ozone as a by-product.  Some release formaldehyde.  Some may even put carbon monoxide into the indoor air.  See the Disadvantages column in the table above.

Zaatari and Dr. Marcel Harmon wrote an article titled Open Letter to address the use of Electronic Air Cleaning Equipment in Buildings, in which they covered in great detail these two problems with electronic air cleaners.  In addition, another twelve of the top researchers in indoor air quality reviewed and supported the letter.  If you want specifics with references, read the letter and add it to your bookmarks.

What are the best ways to clean the indoor air?

I’ll restate what I wrote in my article on UVGI:  Your best bet is still source control, filtration, and ventilation for good indoor air quality, and that’s where you should start.  UVGI can be effective but is best for health care and other facilities where the systems will be engineered properly and overseen by the facilities staff.

Source control means not bringing pollutants into the building.  It also means not generating them with devices like ionizers or photocatalytic oxidizers.  And I shouldn’t have to say this, but if you still allow smoking in your home, you have a huge source control opportunity.

Filtration in homes is often done poorly, but a good HVAC system can incorporate MERV-13 filters with low pressure drop.  A portable MERV-13 or HEPA air cleaner is a good alternative if you can’t get good filtration with your HVAC system, and you can even make one yourself.  Filtration with MERV-13 and higher or with HEPA filters will remove a lot of the particles in the indoor air.

For gases and other pollutants not captured by the filters, ventilation helps.  Adding outdoor air can improve indoor air quality through dilution.  Just make sure you filter the ventilation air, as most indoor PM2.5 comes from outdoor air.  To see how much air exchange you’re getting, monitor the indoor carbon dioxide level.

The main conclusion here is that ultraviolet air cleaners and maybe electrostatic precipitators are the only electronic air cleaners worth considering.  You should avoid all others because at best they may not be effective and at worst they could be making your indoor air worse.  This past year of the pandemic has put a big spotlight on indoor air quality.  With the IAQ workhorses of source control, filtration, and ventilation, we have a chance to make a huge difference in our indoor environments.

Zaatari, however, highlighted the risk of this spotlight:  “Think of a world where after this pandemic we have worse indoor air quality.”  That’s what could happen if we adopt electronic air cleaners over source control, filtration, and ventilation.


Allison Bailes of Atlanta, Georgia, is a speaker, writer, building science consultant, and founder of Energy Vanguard. He is also the author of the Energy Vanguard Blog and is writing a book. You can follow him on Twitter at @EnergyVanguard.

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Air Change Rates and IAQ


Photo of air cleaner on table by Aaron Yoo from, used under a Creative Commons license.


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This Post Has 40 Comments

  1. Wow . Congratulations on such well presented paper. This is the best technical assessment i have seen on this subject matter. It is really good to see options for air quality however there is no 100% solution for pathogens and pollution. For pathogens it needs to be at sterlization level.
    99% claimed by products is bit of hot and miss and misleading the public for pathogens .
    All filters i have worked with become a source oh contamination or ideal environment for pathogens to multiple.

    Life is compromise. Take the best we have.

    1. Matthew, thanks for your kind words. Yes, filters have their disadvantages, as you mentioned. The table above from the EPA document also mentions that used filters can be a source of pollutants.

    2. UV is not the best available! ActivePure Technology is!!! The company is rooted in science will every bit of data found in the website. It’s a true game changer and it has the industry on eggshells because every other technology available is primitive in comparison!

      1. Richard, if this technology is so great, why doesn’t the website explain how it works? The closest I could find is that it’s based on “oxidizing molecules,” which would put it in the oxidizer category. Tell me how much ozone, formaldehyde, and other pollutants it produces as a by-product. This also makes it an additive technology, meaning that it adds something to the air in an attempt to remove or deactivate pollutants and pathogens. Much safer is to stick with source control, ventilation, and filtration. Maybe some of the experts who know more about your technology will add to what I’ve said.

      2. I dont think so, we have RemeHalo and every time it runs for more than a day my wife complains about headache and air become unpleasant. VOC levels remains the same, no change.

        1. You might want to check that unit with an ozone meter.
          Possibly has an ozone splice in the UV lamp.

  2. PHD in bullshit. Your chart is wrong. You don’t use the correct terminology for the industry. Good luck pumping just filters I guess. I know you yourself have not done an independent test on any of the tech you bash.

    1. Al, thanks for your thoughtful and well-documented comment. You really destroyed everything I wrote above with all the evidence you’ve provided. I guess I should shut down the blog and delete this and the other 900+ articles I’ve written here.

  3. Allison Bailes, great article. Thanks for taking the time to aggregate all of this information and organize it in a useful manner. Very helpful to professionals that are constantly bombarded by the manufacturer’s reps.

    1. Thanks, Mark. This is an article that’s been on my list to write for a couple of years. Turns out that waiting till now made it quite timely.

  4. Interesting that Dr Birckx’s first move after leaving government service was to take a job as Chief Scientific Officer (a job she is totally unqualified for) with the manufacturer of one of the major offenders, which has UV lamps that cannot possibly be effective and a “silver catalyst” that could not physically have the results they claim.

      1. GOOD. It kills SARS2 so it will kill Covid19 also. These devices you keep bashing are ETL certified. Sure there are fakes in the market but stop bashing tech that is proven to clean air.

          1. I gave you over 5000 scholarly studies to read and you are up at 1am replying to me. Just go read a few of them please. Filters are great, I know I use carbon filters myself. In conjunction with some of this tech you can remove 99.9% of the VOC’s. I’m trying to help you Doc.

  5. Yes and the mainstream press has totally ignored this. Although The Guardian in the UK did mention it. I noticed that HVAC contractors are now pushing these two companies like mad. Personally I won’t touch any contractor who tries to snow me with pseudo science.

    1. Thanks Allison, excellent article , very clear and easy to understand.

  6. I use the Aerislite and have noticed a Big difference in air quality at least in my bedroom.

  7. Trane just published the independent test results of all of the technologies mentioned above. Not surprising, Ionizers were shown to be about as effective as MERV13 filters. And the most effective technology was HEPA filters with PCO a close second. You can find the summary video on YouTube here:

    1. Kevin, you forgot the part where you say that your company is “Trane’s largest independent distributor of commercial, industrial and residential heating and air conditioning systems and equipment.” That’s what it says on your homepage anyway.

    2. Kevin I can’t find the study on the Trane site, can you post a link?

  8. There is a new product on the market called IVP Air “Heated HEPA”. Simply put, it uses HEPA filters and pulses electricity on one set of the metal separators to heat the HEPA above the temps required to kill captured pathogens. See more here: www dot ivpair dot com.

    1. Likewise, you forgot to mention that your company is a distributor of IVP Air products. I know you put the link in their so people can click your name and find that out, but it’s nice to provide that kind of disclosure when you say nice things about a product you sell.

  9. Allison,
    Thank you for your thorough article on what is best methode to remove airborne contaminates from the home environment. I am already useing several HEPA filters (with and additional activated carbon filter) through out my house. They have a total Clean Air Delivery Rate (CDAR of over 600 CFM). I use these mostly in the automatic mode when at home then often turn them on full when I am away from home.
    I also have a Merv13 filter in my HVAC sytem. I generaly leave this circulating air even when I am not heating or cooling my home. I have found the air very clean however I have purchased a “RGF Reme Halo LED Whole Home in-Duct Air Purifier System REME LED ” and plan to put it in today. They claim the new LED unit produces no Ozone. They claim that it cleans all the air in your home by createing Hydroxal ions (H202) that kill viruses and clumps together small particals so that your HVAC filter will remove these small particals that ususally can get through the filter. Also that the H2O2 ions are at a low safe level. I looked it up and that safe level is below 1 part per billion.

    Please comment. Is this filter safe to use?
    Thank you
    Ron Barnett

    1. Ron, it sounds like you have a really good IAQ system without the new device. Dr. Zaatari and the others on the open letter they wrote hydroxyl ions in with the group of air cleaners to avoid, so I personally wouldn’t put one in my house, even if it doesn’t produce ozone.

      1. Hello Allison,
        Thank you for your Prompt reply. what does Dr. Zaatari and the others on the open letter say about air cleaners that use hydroxyl ions that are at a level of less than 1PPB?

        1. Hi Ron, my two cents based various research papers and internal testing carried out, Allison’s paper is bang on on any additive filtration.

          Be it Ozone, Hydrogen Peroxide, Hydroxyl Radicals etc, working principal remains the same – which is oxidation of VOC’s ( Hydrocarbons) or Microorganisms.

          The oxidation potential measured in Electro chemical volts determine the efficacy, that is how good and fast a radical or ion can oxidise.

          Higher the oxidation potential better the oxidation, this also makes the Nth life of particular ion lower.

          Now here is the catch, most of these independent testing / No harmful by-product etc as MARKETED by various companies test the devices in a very controlled environment and disclosure states Harmful by-product are within limits ( every other manufacturer markets in same way)

          Once these products are installed Residential / Commerical environment, the dynamics of Air completely change the operations of these products wherein they are now placed in uncontrolled environment.

          Due to incomplete chemical reactions, these ions / radicals react with various hydrocarbon present ( TVOC’s) and instead of resulting in harmless byproducts ( CO2 and H2O) they form variant of Hydrocarbons which may be even more dangerous or carcinogenic than the one you wanted to treat.

  10. Curious what you think about negative ions for their own sake. I rather doubt they make a significant filtration difference, but they make me feel happier – like the magical fresh air following a rainstorm.

    First search hit I found says an ozone level <50 ppb is "good", and that devices producing over that cannot be sold in California:
    Of course they sell filters – apparently physical filtration with a "patented PECO (photo electrochemical oxidation) process"…

    Are "negative ions" the same thing as ozone? Is there a "safe" level? Why is turning on my tiny "bathroom deodorizer" a "breath of fresh air"? Or at least a satisfying illusion of fresh?

    1. …no they are not. Any gas molecule /atom can be ionized. Ozone is an oxygen molecule with an extra oxygen. That is O3 instead of the normal O2. OZone is produce in an electric arc or by UV light. The ozone in our upper atmosphere is produced by UV from the sun and helps forms a protective conductive shield around the planet.
      On the other hand, an Ion is simply a molecule/atom with one more extra electron making it a negative ion, or one or more less electrons making it a positive ion. Ion’s can be in an air solution like the ones we are talking about here in this discussion on air purifiers, or they can be in a solution like water. For example dissolving salt (NaCl) in water where the NaCl disassociate and become positive Na ions and negative Cl ions. Water is a polar (though neutral molecule) that pulls the Na and Cl apart into ions.

      Simply put an Ion is atom or molecule whose charge is not neutral, and ozone is an O2 molecule with an extra oxygen making it an O3 molecule.

      Hope that helps and is not too wordy.
      Ron Barnett

  11. Thanks for the clues! I dug some more… It looks like oxygen can form ionic bonds with some metals, but mostly exists covalently bonded to another oxygen atom.

    An oxygen gas molecule (O2) exists as a pair of oxygen atoms joined together by a double covalent bond. Two pairs of electrons are shared by the two atoms. Ozone (O3) consists of three oxygen atoms joined together. One of the lone pairs of electrons from one of the oxygen atoms of an O2 molecule forms a new covalent bond with a third oxygen atom.

    Ozone (O3) is more reactive than oxygen gas (O2) because they have different structures. The double bond between oxygen gas atoms requires a lot of energy to break whereas when ozone reacts an oxygen atom generally splits off quite easily, which leaves behind a stable O2 molecule.
    Oxidation of volatile organic compounds by negative air ions
    Chih Cheng Wu 2004

    NAI means negatively charged small air ions. Superoxide (O2-) is the main negatively charged species in NAI, and is more stable than other ions. The lifetime of NAI depends on humidity, temperature and other factors, and the typical lifetime in clean air is less than several minutes.

    Ozone O3 can be generated by the same electric discharge as ionization, and the amount of O3 generated is related to the material of electrode, humidity, discharge polarity, diameter of the electrode tip, and other factors. Discharge of a corona or a spark can generate ozone (O3), nitrogen oxides (NOx), and hydrogen peroxide (H2O2) when the voltage exceeds 16 kV.

    So – ozone and ionized “superoxide” are chemically different, but can be generated by the same equipment, depending on the ionizing voltage.

    A survey of ionizer studies:

    Lots of confirmation of small particle reduction, main drawback is the possibility of ozone.

  12. I use Blueair standalone air filters at home which have an “ionization chamber” in them but also came in well below the limit in the CA study linked above. I’ve been curious to see if folks in the know would recommend the safe for CA models or if they’d stay away from anything that has ionization all together? Overall, I’m impressed w/ the Blueair products because of their extremely efficient shape. The 411’s use only 10 watts on high speed.

  13. Another great article, Allison.
    I work in the HVAC field. This includes hospitals, labs, and clean rooms. This research reflects exactly what is installed in the systems serving these facilities. It is all high MERV/HEPA filters and fresh air exchange. Critical environments use filtered 100% outside air. I do see some of the germicidal UV lamps – more commonly in public facilities. I come across exactly 0 (that’s zero) electronic, ozone, ionizing, etc. filtration equipment in any of these systems. HEPA filters are NOT cheap to maintain. If these products were as good as the manufacturer claims, why don’t I ever see any? Stop with the crap claims and show me REAL peer reviewed CREDIBLE research.

  14. Hey Allison! This is my third time reading this. It helps me so much. My company sells PCO/UV products and I am sometimes tempted to sell them due to sales, etc. But having great information like this keeps me grounded

  15. I’ve been researching air cleaning options that might help alleviate my worsening allergies. Thanks for providing very clear, concise articles on the subject.

  16. Hey Allison! What’s the most recent scoop on this? Any new studies or developments we can reference when choosing technology that can clean our air?

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