How CNET Tests Air Purifiers

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CNET has tested dozens of air purifiers over the years to help you pick the best ones for your needs -- whether it’s for cold and flu season, to reduce dust and allergies or to deal with a shedding pet. All of our air purifiers are rigorously tested in CNET Labs product testing facility in Louisville, Kentucky. When evaluating our scores for air purifiers, we take into account particle removal ability, energy efficiency, loudness, price and features. Each unit is given a score out of 10 for each criteria, and then receives a weighted final score out of 10.

Editors' Choice and CNET Lab awards

Two air purifiers that won the lab award

After we test air purifiers, we also evaluate the top performers for an Editors’ Choice award as the best purchases for most consumers, based on quantitative and qualitative factors like particle removal, energy efficiency, noise level, price and unique features. This award was given to our current best overall, the BlueAir Blue Pure 311i Max, and our pick for the best cold and flu prevention, the Shark Large Air Purifier HP232.

We also evaluate pure quantitative test results from our rigorous methodology to distinguish a Lab Award winner. Our lab award winner for the fastest particle removal on a high fan setting is the Coway Airmega 400s, achieving a T90 of 21 seconds at the highest fan speed. It also ranked second in overall particle removal and is a great option for large rooms. The Shark HP232 Air Purifier Max earned our other lab award for the fastest particle removal at a low fan setting. It was the top performer in overall particle removal speed, with a T90 of 1 minute and 17 seconds. It was also the cheapest unit to run in terms of energy efficiency.

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How we test air purifiers

Particle Removal (30%): The average amount of time it takes for an air purifier to remove 90% of the particles from our test chamber.
Energy Efficiency (20%): The average energy measured in kilowatt hours used by the air purifier, we also calculate it over the course of a month.
Overall Loudness (20%): The average noise level across low, medium and high fan settings.
Price (20%): We consider how affordable or expensive an air purifier is. Most of our recommendations range between $300 to $800, depending on size.
Features (10%): We consider features like app control, remotes and design elements that help it fit into a room.

The particle removal test

The air we breathe isn't just air. In truth, it's a combination of human-generated and naturally occurring particles. The former is composed mostly of urban, industrial and automotive emissions of hydrocarbons, nitrogen oxides and combustion byproducts, and the latter is mostly represented by smoke from forest fires, sulfates, soot and matter from volcanic activity around the globe.

This gif shows our smoke chamber filling with smoke after lighting the smoke bomb. This image shows our older particle counter rather than the newer model we currently use.

Gianmarco Chumbe/CNET

According to the EPA, some of these microscopic solids and liquid droplets, which can be made up of hundreds of different chemicals, are so tiny that it's almost inevitable to inhale them.

Fine vs. coarse particles

Our custom-built air purifier test chamber sits in the dark, the interior illuminated behind plexiglass by white string lights. It's a sealed, closet-size room that we fill with smoke to test each unit.

In terms of smoke, seasonal allergens and dust, an important consideration in buying an air purifier is whether it has an automatic mode. Certain air particles do not remain consistent throughout the year or even throughout the day. While different types of particulate matter are indistinguishable to the air purifier itself, according to the experts we spoke to, an important consideration for particles such as pet dander is energy draw, because that type of pollutant theoretically remains consistent in your home and necessitates constant use of an air purifier.

We test our air purifiers against fine and coarse particles. Coarse particles, including PM10 and PM2.5, which are particles with diameters of less than 10 and 2.5 micrometers, respectively, pose the greatest risk to human health once inhaled. They are absorbed deeply into the lungs and even into the bloodstream, impairing the proper functionality of the lungs and heart. At PM2.5, these include combustion particles, organic compounds and metals.

GreyWolf PC3500 Particle Counter against a purple background

At PM10, these include dust, pollen and mold. Large coarse particles are greater than PM10 and include fine beach sand (PM90), which is less of a concern because it doesn't usually enter the lungs, but can still irritate your eyes, nose and throat.

Fine particles are 2.5 micrometers in diameter and smaller. These include ultrafine and nanoparticles, which have diameters of less than 0.1 micrometers.

Smoke chamber test

Glass measuring cups containing potassium nitrate, sugar and baking soda sit beside a test tube containing a mixture of the three, plus a fuse. This is one of the "smoke bombs" we use during our air purifier tests.

Using the GreyWolf PC3500 Particle Counter, we were able to verify that 0.5 grams of our smoke bomb dry mixture produces roughly between 590 and 610 million particles per meter cubed. The device is able to count particles of different sizes, including PM2.5 and PM10, and it logs this data once every 15 seconds. Although we're able to count particles of different sizes individually, it's the total number of particles we care about, which is the sum of all particles of different sizes.

Close up of the smoke bomb before ignition.

We prepared a 0.5-gram smoke bomb, which is ignited via the ignition port after installing the air purifier and ensuring proper sealing. Once the air in the chamber becomes particle-saturated (greater than 580 million particles/m3) we turn on the air purifier in question. The data extracted from the particle counter allows us to accurately track the impact that the air purifier has on the particle count in real time.

Noise level

Using a decibel meter, we measure how loud the air purifiers are at their low, medium and high fan settings. This is particularly important if you plan on having your air purifier on in your bedroom overnight and you don't want it to disrupt your sleep. We perform this test in our sound-controlled studio to make sure that the decibel meter picks up only the sound of the air purifiers, excluding other possible sources.

To give you a frame of reference, a quiet whisper is about 25 decibels. A normal conversation can range from 60 to 70 decibels. A vacuum cleaner ranges from 65 to 80 decibels. A subway train at 200 feet away is as high as 95 decibels. With most of our air purifiers no louder than 65 decibels even at maximum fan setting, you're typically looking at a noise level that's on par with a normal conversation. Generally, noise level isn't weighted as heavily as other factors, but it does matter, especially if you're looking for an air purifier

Energy consumption

To evaluate how much energy an air purifier consumes, we use a HOBOware data logger, an energy monitoring device to measure how much power each air purifier consumes at different fan settings. We can take this measurement and estimate the cost of running the air purifier over the course of a month in different states. Knowing the energy draw for your air purifier can make a difference to your energy bill, and we weigh it as a factor in our evaluation.

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