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How I Rate Air Purifiers
This guide covers how I rate air purifiers for their impact on your health. It explains what all the little symbols mean under the air purifiers in the Healthy Design Shop.
You can use it as a guide when searching for air purifiers anywhere— the same information applies wherever you go.
Read more about why I rate air purifiers and materials here.
My guide to air purifiers is focused completely on your health, which sets it apart from others.
Most air purifier review websites or are based on anecdotal in-home use (“I noticed less dust,”) aggregate customer reviews, ease-of-use, aesthetics— and sometimes favor unproven, or even harmful technologies (ozone generation, for example).
Luckily, there are a handful of air purifier testing platforms and news outlets that actually conduct systematic testing of air purifiers using high-precision particle counters. They’ll typically pump the same amount of smoke in a closed room of a certain size and time how quickly the purifier filters the air. This kind of testing is crucial because air purifiers aren’t regulated in the United States, and the effectiveness of any given purifier depends not only on the kind of filter it contains but also how efficient it is as actually bringing in dirty air and re-dispersing clean air back into the room. For example, a medical grade, H14, true HEPA, filter sounds best— but because it’s so dense, purifiers with an H12 filter and higher air flow often perform better. Real-life testing allows us to know this.
For Interior Medicine, the ability of an air purifier to filter particulate matter from a room, as above, is a baseline starting point for what makes a good pick, as the health risks of particulate matter are high. However, I also think more attention should be paid to filtering Volatile Organic Compounds (VOCs) from indoor air, which also contribute to asthma, allergy, frequent headaches, lung issues, and can even contribute to cancer (like formaldehyde and benzene). And, there are four main features included in air purifiers that have a potential negative impact on health: generating ozone, emitting excess blue light, operating at a high noise level, and WiFi.
To stay organized and unbiased, I use the Standard Rating Scale to rate air purifier components from healthiest to least healthy. Here’s a quick reminder about what each level on the scale means:
Healthiest option available.
Healthy, but doesn’t meet the strict standards of the blue dot.
Minimal health risk. Verified to be healthier than its standard counterpart.
Caution is warranted.
Well-known harmful effect on health and should be avoided whenever possible.
Here are the air purifier-specific requirements for meeting each level on the scale. Read on below for more details about terminology and specific examples.
Click on bolded statements to see links to research.
Particulate Matter Filtration
What is Particulate Matter (PM)?
A fancy word for particles, Particulate Matter in your home comes from dust mite fragments, mold spores, and sources of combustion— like cooking, or using a toaster. If you live in a part of the world with wildfires, the smoke that comes into your home is also Particulate Matter.
These particles pollute your Indoor Air Quality quickly, and if they’re not cleared out of the home, they can irritate the lungs or combine with other harmful pollutants.
Particulate Matter is talked about as either PM 10 or PM 2.5. This just refers to how big the particles are, because the different sizes cause different problems.
Pollens, molds, dust, and dust mite fragments are particles that are below 10 microns in size, and their main effect is irritation of the throat and lungs. They can exacerbate asthma, and make it harder for the lungs to clear out viruses.
The particles smaller than 2.5 microns (PM 2.5) are more concerning, as these are the ones that can pass through your lungs and directly into your blood stream. Things like wildfire smoke, and the particles and chemicals released from cooking fall in this category.
Why is Particulate Matter dangerous?
We know that PM can cause coughing, wheezing, and exacerbations of asthma, and reduced ability to remove bacteria and viruses from the lungs.
Amazingly, it can also increase the risk of heart attack and worsening of heart failure, and increase ER visits, hospital admissions, and premature deaths.
PM is increasingly linked with dementia and Alzheimer’s Disease.
What is a HEPA filter?
HEPA means High Efficiency Particulate Arrestance. HEPA filters capture 99.97% of particles that are 0.3 microns in size. Due to complicated physics, 0.3 microns is the hardest size of particle to capture. It’s actually easier to capture particles both larger and smaller than this! A regular HEPA filter captures particles 100 times smaller than 0.3 microns with almost 100% efficiency.
Are HEPA-style or 99% HEPA filters the same as regular HEPA filters?
No! The terms HEPA-style, HEPA-like, 99% HEPA, and others, are not real HEPA filters. These do not filter particles with the same efficiency as HEPA filters, and may not filter small particles at all.
What is an ULPA filter?
ULPA filters are Ultra Low Penetration Air filters. They can actually capture even more particles than HEPA, but, they do not work as well as HEPA filters, because they are so tight, that air has such a hard time getting through them. They have a very low CADR (clean air delivery rate).
They may sound better, but they are not recommended, because they clean very small amounts of air.
What is a PECO air purifier?
PECO stands for PhotoElectroChemical Oxidation. It oxidizes micro-organisms, effectively killing them. This technology has been around for decades, but in 2016, was added to the Molekule air purifier. Unfortunately, it was found in multiple tests unable to filter out harmful particulate matter like PM 2.5 or other gasses nearly as effectively as regular HEPA filters can. The Molekule company was forced to retract these claims. While it is an interesting technology, with potential future applications, it remains just not as effective as regular HEPA filtration. The Molekule filter now has a HEPA filter and a PECO filter. This is a major and well-publicized version of healthwashing.
What do CADR and CFM mean?
CADR = Clean Air Delivery Rate. CFM = Cubic Feet per Minute.
These are two metrics commonly used to measure how effective an air purifier is.
The CFM is how much of a room’s air volume is filtered each minute. A general rule of thumb is to look for at least 100 CFM for every 250 square feet of space.
The CADR is the CFM multiplied by the efficiency of the filter. It only applies to particulate matter (it does not measure how well VOCs or microbes are filtered). The CADR is a fine measurement if the purifier has a true HEPA filter. It is not useful for a purifier with a very high CFM but a non-HEPA filter: this would mean that air moves through rapidly, but doesn’t actually get clean. A good rule of thumb: choose a HEPA air purifier with a CADR 2/3 of your room’s area. A 20 x15 square foot room has an area of 300. So, a CADR of 200 minimum would be ideal.
These are important measures to consider, and typically play in to how well an air purifier does in testing. But, it’s not the whole picture: the HEPA filter density matters, too. This is why I rely on real-world testing rather than exclusively on these numbers.
Is there technology superior to HEPA?
All regular HEPA filters are capable of removing particles 100 times smaller than 0.3 microns at nearly 100% efficiency— it’s boring, but true.
Claims about filtration technology that’s more effective than HEPA is not yet true.
Gas (VOC) Adsorbent
What are VOCs? Why are VOCs harmful?
VOCs are Volatile Organic Compounds. They are gasses, and many have harmful properties, like formaldehyde. VOCs, including formaldehyde, are found in the home in the following places:
Glues holding furniture together
New carpet or vinyl flooring
Sealants, stains, and finishes on wood furniture or flooring
Engineered wood and particleboard
Paints
Area rugs with synthetic backing and glues
Cleaning products
The “new house smell” is simply VOCs off-gassing into the air.
Formaldehyde and benzene are VOCs released from daily indoor products and are both known carcinogens. There are thousands of other VOCs which contribute to asthma, allergy, frequent headaches, and lung issues.
Interestingly, VOCs usually have an odor, but not always.
What is a gas adsorbent?
Gasses are not particles, and therefore cannot be captured by a HEPA filter. An adsorbent, like activated charcoal, is used instead. Adsorption is a chemistry-based process that works by having gas cling to the surface of the adsorbent, where it stays bonded with surface energy.
Do you need a gas adsorber?
If you are using an air purifier near the kitchen, in a room with lots of activity, or with materials that may be doing some off-gassing (like a couch or mattress made with regular foam, for example), choosing an air purifier with gas adsorption is important.
If you have asthma, allergies, or chemical sensitivities, it can be important.
If you are using an air purifier in a room without off-gassing, cooking, or much activity, you might choose to forgo a gas adsorbent. A good way to determine whether your room has many VOCs in it is by using a high-quality indoor air quality monitor to get a reading.
What does activated carbon (charcoal) do?
Activated charcoal is a common gas adsorbent that is used in purifying air. Wikipedia explains it best— it starts as carbon, and is activated like popcorn kernels are popped into popcorn: it becomes larger, with more surface volume, so more gas molecules can bond to it. Activated charcoal is very good at capturing a wide range of VOCs from the air.
What mineral mixtures are added to activated charcoal and why?
Sometimes, mineral mixtures are added to activated charcoal to increase the types of VOCs that can be adsorbed from the air. Potassium iodide, potassium permanganate, and zeolite, are three different mixtures that are useful when added to activated charcoal. Each has a different pore size that can adsorb different chemicals better than charcoal alone. Zeolite is capable of adsorbing formaldehyde, which is important, because charcoal cannot do it on its own.
Why are air purifiers only tested for the PM filtering ability and not their VOC ability?
So far, Particulate Matter (PM) has received almost all of the attention for air purifier abilities. This is partly because HEPA filters are the primary component of air purifiers, and very few contain VOC-adsorbing charcoal and minerals— though this is changing as awareness of VOC impact on health rises.
Particulate Matter is also a major global health issue, contributing to millions of excess deaths yearly.
Finally, particulates are also very easy to measure with handheld devices, and VOCS are trickier. There are VOC-measuring devices, as seen in indoor air quality monitors, but they generally cannot differentiate between “bad” VOCs and “OK” VOCs yet. For example, residential devices that claim to be able to measure formaldehyde in the air have mostly been debunked as just reading general VOCs, like the scent of an orange, for example.
Potential Health Risks: Ozone Generation
What is UVGI?
UVGI stands for Ultraviolet Germicidal Irradiation. This technology does have the ability to kill microbes, however, in most home air purifiers, the air flows by it too quickly, leaving inadequate contact time for it to be effective. UVGI also does not address the main issues in most homes, which are particulate matter and VOCs, rather than microbes.
What are air purifiers with ionizing technology?
Ionization is a very popular technology add-on for air purifiers. If they are strong enough, they emit ions, which stick to particles in the air, and cause them to become “heavier” and stick to items in the room. Sure, the air is cleaner temporarily, but now the particulate matter is settled on your stuff. Worse, if an ionizer is strong enough to do this effectively, it is also generating ozone, which is toxic to your lungs and causes inflammation.
Why are air purifiers with ozone generation unsafe?
Ozone, O3, is the free radical version of oxygen. It is highly reactive with particles in the air, and also highly reactive with cells in your body. Breathing in ozone can cause lung inflammation and respiratory issues.
Why is blue light considered a potential health risk?
Exposure to blue light, especially in the bedroom, where many people use their air purifiers, has many negative health outcomes. Even a very small amount of night time light (5 lux) can disturb your clock genes and cause circadian rhythm problems.
Too much blue light is associated with eye strain and macular degeneration, and incredibly, an increased risk of breast and prostate cancer. In contrast, red light has none of these effects.
Read more about blue light here.
Potential Health Risks: Blue Light
Why is noise considered a potential health risk?
When sound is unwanted, and affects the health and well-being of people or other living creatures, it meets the definition of noise pollution.
The EPA confirms that it’s not just an annoyance, but is as important to your health as other types of pollution are, like air or water pollution. Excess noise, especially at night, can actually contribute to heart attack, and have negative impacts on cardiovascular health, including high blood pressure.
Read more about noise pollution here.
Potential Health Risks: Noise Levels
What decibel level is reasonable for air purifiers?
Air purifiers are meant to be run 24/7 on their low setting, unless during times of high air pollution (wildfire, burning food indoors, or acute off-gassing from new furniture, for example.) I consider anything under 50 decibels (dB) to be quiet enough for bedroom use. For reference, 50dB is about the sound you’d hear in a quiet office, or coming from a quiet refrigerator. It is generally considered a reasonable and safely quiet level for sleep.
Why is WiFi considered a potential health risk?
WiFi devices use radiofrequency electromagnetic fields (RF-EMF) to send information. This has become a common feature in air purifiers, so that you can control them via your smart home app or phone when you’re not in the room.
As far as health impacts go, EMFs surround us constantly, and have since the beginning of time. The man-made ones bring us enormous benefit, and research results are very mixed on whether there are adverse health outcomes. On the other hand, some people know that EMFs very strongly affect them. And, since man-made EMFs are still relatively new to our world, and I don’t know the long-term effects yet, some countries and people are being extra cautious.
I believe the bedroom should be a place for healing and regenerative sleep, so out of respect to the unknown and out of an abundance of caution, I highlight air purifiers with a WiFi-free option at this time. Many also have WiFi options available for a slightly higher cost, if you decide that’s convenient for you!
Potential Health Risks: WiFi
Third Party Certifications
Are there any 3rd party certifications for air purifiers?
Very few. And, the ones that exist are voluntary. Air purifiers are a very inconsistent and unregulated industry, especially for portable in-home air purifiers that the majority of people need.
CARB (the California Air Resources Board) and UL (Underwriters Laboratories) are third parties that verify that air purifiers don’t generate ozone.
AHAM (Association of Home Appliance Manufacturers) has standardized the clean air delivery rate (CADR) but it only applies to how well a purifier can clean air with dust, pollen or tobacco smoke (not VOCs, viruses, or other contaminants).
HEPA is not a 3rd party certification, but legally, a company can only say their filter is a HEPA filter if that is indeed true.
What are 3rd party certifications and why do they matter so much?
Third-party certification means that an independent group that didn’t make the product, and has no financial ties to the product, has reviewed, tested, and verified the claims that the company making the product has made.
Third party certifications protect you. Just like greenwashing makes products appear better for the Earth than they really are, some companies intentionally make their products seem healthier for people than they really are, too.
Can I depend on 5-star reviews to find a good air purifier?
Ratings that rely on 5-star customer reviews, or blogs that aggregate customer reviews, are not reliable.
These are not based on particles, science, or effectiveness. Instead, they’re based on experience, which undoubtedly hleast effective air purifiers on the marketas some measure of a placebo effect— buying something expensive certainly has the power to make you feel like your air is cleaner (even when it isn’t).
For example, the $800+ Molekule had great reviews before it was discovered to be one of the least effective air purifiers on the market— likely because it was aesthetically pleasing and had great marketing. They have since been forced to retract their claims and have added a regular HEPA filter to their machines.
Other
Do probiotic air purifiers work?
Probiotic air purifiers are relatively new to the market. While I love the idea of probiotics incorporated into homes, this is not an effective way to remove fine particulate matter (PM 2.5) or VOCs, which can have serious consequences for cardiovascular, lung, and cognitive health, from your air.
Do water-based air purifiers work?
No.
Water-based air purifiers do not have HEPA filters, and therefore are not capable of cleaning the air effectively.
