With increased demand due to the pandemic, the market for air purifiers has become even more competitive. Companies vie for business using slogans and claims which can be difficult to verify. Fortunately, there are a number of standards that can be used to determine which air purifier will best meet your needs.

What kind of filter does it use?

HEPA filters are the industry standard for effectiveness. To be designated a True HEPA filter, it must be able to trap 99.97 percent of particles that are 0.3 microns. But, in reality, HEPA filters are actually capable of filtering out particles of almost any size.

A True HEPA filter can trap dust, mold, smoke, pet allergens, PM2.5 (dangerous particles that are 2.5 microns or smaller), and even bacteria and viruses… which is why the CDC has recommended them for help in slowing the spread of COVID-19.

Beware of companies that call their filters “HEPA-like” or any similar term.  Those phrases are used for filters that have not passed the industry standards and usually mean that they are less dense and unable to capture the smallest and most dangerous particles.

HEPA filters are very effective at trapping particles, but not so helpful for removing gas.  Purifiers that contain activated carbon filters are your best bet in filtering out volatile organic compounds (VOC’s) and odors.

That’s because activated carbon is extremely porous. During a process called adsorption, the pollutants that enter the filter stick to the outside of the carbon. As long as there is an open adsorption site (and, in activated carbon there are plenty), the pollutants will keep sticking to the carbon.

To get the best possible protection, look for purifiers that have both HEPA and activated carbon filters.

Filters work best when changed regularly. In general, HEPA filters should be changed every year and carbon filters should be replaced every three to six months.

Is the purifier AHAM certified? 

If a purifier is AHAM certified, it means that it has been tested and rated by the Association of Home Appliance Manufacturers for its ability to clean tobacco smoke, dust, and pollen from a room.  AHAM certified purifiers provide CADR numbers so that you can compare different purifier’s performance for various pollutants.

What’s the CADR?

CADR stands for Clean Air Delivery Rate. It’s the rating system designed by The Association of Home Appliance Manufacturers (AHAM) as a way to measure the performance of residential air purifiers. CADR provides a standard to help keep consumers from being deceived by misleading marketing campaigns.

CADR measures how much air is filtered in an hour for a particular pollutant. The number you see represents how much volume of air is actually cleaned within an hour from the designated pollutant.

CADR numbers are given for smoke, pollen, and dust. Basically, the higher the CADR number, the faster the air purifier filters the air. However, rather than just going with the highest number, it’s best to also factor in the size of the room when deciding which air purifier to purchase so you don’t end up wasting energy and money.

A good way to determine the ideal CADR is to follow AHAM’s 2/3 Rule which says that generally, the CADR of your air cleaner should be equal to at least two-thirds of the room’s area.

For example, a room that is 10 feet by 12 feet has an area of 120 square feet. ⅔ of 120 is 80, so an air cleaner for that room would ideally have a smoke CADR of at least 80.

What’s the ACH rating?

ACH rating stands for “Air Changes per Hour”. The ACH number shows the relationship between the volume of air and how much air the purifier moves per minute (CFM). Generally speaking, an ACH rating of 7x means that the full air volume is exchanged seven times every hour. However, this number is based on a standard 8-foot ceiling.  If you have higher ceilings, there is a higher volume of air, and the ACH will be lower.

The ACH rating is helpful because it can give you a quick way to compare purifiers. It’s typically best to look for air purifiers with at least a 4x ACH rating.

What is the CFM?

CFM stands for cubic feet per minute, also known as airflow.  It’s the amount of air that passes through the purifier at a certain point. The higher the CFM count, the larger the space the air purifier can clean. The right CFM value is important so that there is proper airflow in the room and an ideal turnover of air.

The formula for measuring CFM is Length x Width x Height x (Air Changes per Hour) / 60 min.

Most standard rooms in homes or offices need about 6 air changes per hour. However, larger rooms often require more changes. It’s important to consider both the size of the room and how many pollutants are in the air.  For instance, kitchens generally have lower air quality than a bedroom or office.

A basic rule of thumb is that you need about 100 CFM for each 250 square feet of space. A standard room air purifier typically has around 400 CFM.

How much noise does the purifier make?

Air purifiers work by moving air, which typically results in at least some sound. Unfortunately, the air purifier industry does not have standards for sound emissions. In fact, manufacturers are not obligated to reveal any specifics on noise levels. But, most reputable purifier companies do give some information on noise level, as measured in dB(A).

For perspective, rustling leaves rate at a dB(A) of 0 and a lawnmower rates at about 80 dB(A).

A very quiet air purifier would rate at around 10 dB(A) and a more typical one would be 20 dB(A).

But, the dB(A) alone isn’t enough.  For a true assessment, the decibel levels should be compared at equal CFM levels. For instance, it isn’t accurate to say that a unit moving 390 CFM that is producing 67 db(a) is louder than a unit moving 100 CFM unit that produces 45 db(a).

Some other factors to consider when comparing noise.

  • The actual quality of the sound: 40 db on one system may have a more pleasant sound than 40 db of another.
  • Your personal perception of the sound. Just like taste and smell, we each perceive sound differently.
  • The environment that the unit will be operating in.  The more ambient noise, the less you will notice the air purifier.  For instance, a busy office versus a quiet home.

In short, while the numbers are helpful, the best way to determine if an air purifier is right for you is to actually listen to it operating at different settings.

Does the purifier use ozone?

The pandemic has brought new attention to ozone purifiers for their capability to destroy bacteria and viruses.  Unfortunately, they can also do major harm to our bodies.

Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule that is necessary for us to breathe. The third oxygen atom can detach from the ozone molecule, and re-attach to molecules of other substances, changing their chemical composition.

It’s this third oxygen molecule that interacts with organic material like viruses outside of the body, changing their composition so that they can’t infect us.  Unfortunately, the extra oxygen molecule can also interact with substances inside our bodies, creating a range of health issues like chest pain, coughing, shortness of breath, and throat irritation.

Because there isn’t really any government oversight over purifiers, manufacturers are able to continue marketing ozone purifiers by avoiding making specific medical claims about the devices.

The lack of government oversight is another reason that it’s so important to do your own research before purchasing an air purifier.  In general, look for high-quality purifiers that use True HEPA filters, carbon activated filters, and are AHAM certified.