Air Purifiers Buying Guide: What to look for and… What to avoid

The fact is… it is a buyer beware situation and you would be surprised at the crap sold out there. I have tested literally… I don’t recall… 80 different models of air purifiers over the years when I volunteered in the homes of people with sick family members.

I am obsessed with the topic after we almost lost our 2-year old daughter to air pollution in 2008 seven months after we moved to New Delhi, India. I am a founding member of Help Delhi Breathe. From time to time I contribute to #MyRightToBreathe and the many associated NGOs and individuals.

I have audited schools, hospitals, office buildings, and meeting halls and just love testing, observing and writing about air quality and Clean Energy. I speak at air quality events. I monitor air quality. I love talking about CleanTech and Clean Energy. I am currently a consultant at WHO on (you guessed it) …air pollution (i.e., monitoring, community engagement, and public policy).

So here are all those years and hours of experience in a nutshell.

In order to purchase an effective air purifier, look for a few things (Copyright 2015 Jeffery K Smith)

Look for:

1- The filter — High-Efficiency Particulate Air (HEPA) efficiency rating of (H13 or H14). Efficiency ratings higher than these are okay as long as you understand that in heavily polluted environments you will need more than one machine in the same room (with the exception of a small bedroom). Read more about super-efficient filters later under the ‘Avoid’ list. H11 and H12 efficiency rated HEPA filters still have many uses. Read more about that later too;

2- A high Clean Air Delivery Rate (CADR) which translates to the number of times the total volume of air in a room is likely to be cycled through the filter within an hour when operated on the highest fan-speed setting;

3- A fine Pre-filter to protect the HEPA filter. Pre-filters capture larger particles and can usually be cleaned again and again. HEPA filters can’t be washed without damaging them;

4- Are Replacement filters easily available?

5- Filter Change Indicator to save money. These are sometimes just ‘timers’ so do not rely on them alone;

6- Portability of the air purifier (wheels or a lighter weight will allow you to move them from room to room);

7- Large, heavy, gas filters. If you can afford these systems, those with several kgs of Activated Carbon and/or Alumina to remove some of the Volatile Organic Compounds (VOCs) and some NOx if you live near traffic congestion. NOTE: If you are concerned that the activated carbon might come from one of those antiquated wood- or coconut shell-burning facilities, then call the manufacturer to find out the source countries and methods for their activated carbon.

8- The energy rating or watts per hour used.

Avoid these things when purchasing an air purifier:

1- an Ionization filter technology that generates measurable Ozone (some ionization technology balances the positive and negative ions and is described as Ozone neutral). Ionization that is not balanced by producing both positive and negative ions can generate trace ozone that accumulates in homes with little to no poor ventilation. If the room is properly ventilated, then the Ozone and for that matter harmful toxic emissions from Volatile Organic Compounds (a.k.a., VOCs are emitted from manufactured construction materials, goods, and furniture, carpets, some plastics, cleaners, disinfectants, glues, paints, varnish, even perfumes, make-up, deodorants, dry-cleaned fabrics and more) will not accumulate. (see number 10 below for more about the kinds of air purifiers that emit ozone);

2- Some OEM or lesser-known brand machines and manufacturers will sell you a nice-looking machine with an H11 filter inside (they could put an H13 in there, but, that bites into their profits).

What’s the harm? None really, I never minded having cheaper filters to catch most particles. It is a good strategy to supplement your more expensive machines and save money on filter replacements. So What’s the problem with H11’s, Jeff? I hate it when the dealers sell an H11 (95%) or like the Daikin (I describe below) with 50% efficiency and charge the same price or more than the many other dealers that provide True HEPA filters of H13 ratings or higher. It is as if you bought a Maruti Suzuki Kizashi (2.4-liter engine) and later found that it has a Maruti Suzuki Alto engine (1.0 liter) inside. You get all the nice features and luxury interior with a good-looking exterior. But… you would feel ripped-off paying 17 lakh (USD $23,000) for a 4 lakh (USD $6,000) car’s engine. Update: If you live in India and want to know which OEM brands in which I have found cheaper H11 filters (costing them INR 1000 USD $14 or less) when they are charging INR 28,000 (USD $400) and more for an air purifier they get from China with the filter for INR 6,000 (USD $85) or less, then write to me privately. This is confirmed as I also tested them at showrooms and events. this is not a situation in which the reseller “switched the filter behind our backs” occurred.;

3- Expensive Replacement filters

4- Poor quality HEPA-Type or HEPA-Rated filters. These are marketing ploys to confuse and sell lower-cost filters. I can list many machines sold in Delhi by top brands that have crap filters in them that will not be more than 50% effective in reducing particulate in northern Indian megacity winter conditions;


5- HyperHEPA and ULPA filters that have a low CADR because they are “too efficient”. Some are so efficient that it reduces the number of times that the particulate pollution in the air of a room gets cycled through the filter within an hour. These kinds of machines with ULPA or HyperHEPA filters are designed for lower pollution level environments. These super-efficient and amazing machines are not designed for such elevated levels of PM2.5 and PM10 fine and coarse dust particles as we see across northern India from October through February every year.

Exception: I used these systems in our bedrooms. But, I had to have a lower cost system in the room to assist these medical-grade type of machines. It’s damn expensive. But, more than one family member was sick from the pollution. We decided to have the advantages of both. “Avoid” them, though, if your budget doesn’t allow for you to have two machines in the same room;

6- Machines that intake air from too close to the floor level. There is too much PM10 and larger coarse dust that will be pulled into these units and the pre-filter becomes clogged very quickly. Slowly, the airflow (air exchange or CADR) rate will become lower and will be difficult to detect when the pre-filter or filter needs to be cleaned or replaced. Workarounds: a- Use a household PM2.5 air quality monitor to detect when your room is becoming too polluted (caution: you will still have to constantly check the pre-filter as you will not be sure if the ambient particulate levels are rising or the filter is clogged!) b- Raise the machine up off the floor with a wall-mount or other safe mechanism;

7- Machines with fans that are too loud. Many of the super-efficient filters described above must be operated on the highest fan setting as the pressure resistance of the filter is so great that the CADR has almost no chance to keep up with the ambient particulate pollution entering the home (nearly every home I entered with a HyperHEPA filter had the fan speed on medium at most. The high setting is deafeningly loud though that is how the machines CADR is rated.;


8- Purchasing an air purifier that is:

a. too small (those desktop things mostly), or

b. has a fan speed that is too weak or

c. too poorly designed and allows air inside the cabinet to pass around the filter rather than through the filter;

These will not circulate the air in a room through the filter ‘several’ times (or in some cases even one time) in an hour;

9- NEVER use the ‘automatic detect’ setting on any air purifier unless you live in a very clean country. The built-in particle sensors that enable this energy-saving feature will detect the air purifier’s own clean air bubble and shut off and stay off while most of the rest of the room slowly climbs toward ambient pollution levels often into hundreds of micrograms per cubic meter! You will spend a load of cash even paying extra for the energy-saving feature. But, it will not protect your family.

10- AVOID Machines with Ultra Violet systems and/or PCO PhotoCatalytic oxidation. These features are add-ons that many manufacturers use to differentiate their machine from others and to be able to charge a higher price. But, these are not needed in most scenarios. Concordia University researchers found formaldehyde is produced by PhotoCatalytic oxidation. But, that is one study.

Ozone is produced by most UV light lamps at trace levels and can slowly accumulate to unhealthy levels especially in buildings and homes with little or no ventilation (we seal up our homes and buildings sometimes too much to keep the PM2.5 out). Ozone causes many respiratory symptoms (i.e. wheezing, shortness of breath, asthma, and COPD). Ozone damages the epithelial cells within the lungs and research has shown that Ozone sensitivity in primates remains throughout life. Children are especially vulnerable to the health effects of ozone exposure as lung development continues from birth through ages 8-12 years. According to current research, after fine particulate, ozone causes the most health effects and premature deaths are attributable to air pollution. UV light is used to damage the DNA of airborne viruses and bacteria to prevent them from reproducing. When one considers the fact that the viruses may never pass in front of the UV light several times and most certainly do not remain under the UV light long enough to be damaged at most fan speeds that these combination air purifiers operate at, then it really doesn’t benefit the household or home user. Some newer UV technology using quartz bulbs has been developed that does not emit harmful ozone at all (researching this still; for example, GE 219 quartz tubing is only certified as “not emitting ozone” by the manufacturer according to the sources I have found so far.). I suggest that you leave the UV light filter off if your air purifier has this feature.

Most germicidal UV ‘filters’ in buildings and household air purifiers emit light at a short wavelength between 255-280 nanometers. These lower-cost bulbs that are not quartz still produce trace levels of ozone. If the room is properly ventilated, then the ozone will not accumulate. You can ask the manufacturer if the UV bulb is quartz or not. But, only believe trusted manufacturers that have published this online (and not in a Snapdeal reply to a customer), I mean on their official website;

11- The Daikin MC70MVM6 was only able to capture about 50% of PM2.5 particles in my tests. The filters are not HEPA. They are not much more efficient than pre-filters. This little machine belongs in homes that experience levels of ‘relatively low’ PM2.5 particulate pollution less than 35ug/m3 as is common in the Western nations with better emissions controls for industry, power plants, and vehicles and with better fuel quality. This machine relies on a photocatalytic filter that is not actually good enough for northern India’s wintertime pollution levels. This is not worth ₹26,000 (USD $450 circa 2015) in my opinion.


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