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To help narrow down our air purifier picks, we gathered 14 of the most popular models at CNET Labs’ product testing facility in Louisville, Kentucky, where we put them through the same rigorous battery of tests. Working with trusted lab collaborator Eric Snyder, our goal was to determine which air purifiers delivered the best in terms of particle removal efficiency, energy consumption, and quietness, while also evaluating their respective feature sets and value. Join us as we reveal the science behind our thought process.
The particle removal test
As you may already know, the air we breathe isn’t just air. If you were to walk outside in the middle of the night and turn on a flashlight, you would witness a universe of tiny fragments floating around and being carried by the wind. What is this stuff anyway?
In reality, it is a combination of anthropogenic (man-made) and naturally occurring particles. The former consists mainly of urban, industrial and automotive emissions of hydrocarbons, nitrogen oxides and combustion by-products, and the latter consists mainly of smoke from forest fires, sulfates, soot and matter from volcanic activity around the world. We breathe a mixture of all of these at all times.
According to the United States Environmental Protection AgencySome of these microscopic solids and liquid droplets, which can consist of hundreds of different chemicals, are so small that inhaling them is almost unavoidable. PM10 and PM2.5, particles less than 10 and 2.5 micrometers in diameter respectively, pose the greatest risk to human health because, once inhaled, they travel deep into the lungs and even into the bloodstream, affecting the proper functioning of the lungs and heart.
Air purifiers are supposed to help us improve our indoor air quality by removing these types of particles from the air — but how well do they do it? That’s where our CNET Labs team comes in. Simply put, our mission was to create an environment in which we exposed each air purifier to particle-saturated air of roughly the same concentration and evaluate how quickly and efficiently they got the air back to breathable conditions.
To achieve this, we needed to find a way to produce a quantifiable and reasonably repeatable amount of particles; an environment or “test chamber” in which to house these particles and the air purification units; and an accurate particle counter to act as our monitoring device and allow us to visualize this data. Here’s what we came up with:
Custom made smoke bombswhich are made up of 50% potassium nitrate (KNO3), 40% sucrose (sugar), and 10% sodium bicarbonate (baking soda), and a safety fuse for safe, remote ignition. The sugar acts as our fuel source, while the potassium nitrate acts as an oxidizer, and the baking soda ensures that our dry mixture burns slowly and evenly.
Us test chamber for air purifier was designed and built by Eric and myself. Features include a clear plexiglass front panel and glove access on the right side that allows us to operate the air purifiers, a particle counter holder for our control device, two fans that keep the air and smoke mixing in the chamber, vents that keep a small amount of fresh air flowing, an ignition port to ignite the smoke bombs from outside the platform, and an exhaust port that safely removes residual smoke from the chamber and building after each test. The chamber is not hermetically sealed, but it is tight enough to ensure that no dangerous amount of smoke escapes to the surrounding area.
Using the Temptop PMD331 particle counterwe were able to verify that just 5 grams of our dry smoke bomb mixture produces approximately between 590 million and 610 million particles per cubic meter. The device can count particles of various sizes, including PM2.5 and PM10, and it records this data every 15 seconds. Although we can count particles of different sizes separately, it is the total number of particles that we care about; that is, the sum of all particles of different sizes.
After figuring out the basics, we perform our test procedure as follows: we turn on the particle counter and let it run continuously. We prepare a 5-gram smoke bomb, which is ignited via the ignition port after the air purifier is installed and a good seal is ensured. Once the air in the room is saturated with particles (more than 580 million particles/m3), we turn on the air purifier in question. The data extracted from the Temptop allows us to accurately track the impact of the air purifier on the number of particles in real time.
Under normal conditions, that is, when there was no smoke in the test chamber, the total number of particles that the Temptop reported was about 10 million. So you can think of this as the ‘finish line’ of this race to remove particles. In our test logic, the faster the air purifier reduces the number of particles to below 10 million particles per cubic meter, the better. We perform this test twice for each air purifier, once on the lowest fan setting and once on the highest fan setting to visualize the operating range of each unit. Check out the results for each unit we tested on both low and high fan settings in the GIFs below:
The sound level test
This is a simple test, but it tells us a lot. Using a decibel meter, we measure how loud the air purifiers are on their low, medium, and high fan settings. This is especially important if you plan on having your air purifier in your bedroom and running it all night without disturbing your sleep.
We perform this test in our sound reinforcement studio to ensure that the decibel meter only picks up sound waves from the air purifiers and excludes other possible sources. The lower this number, the quieter the air purifier is. You can see the results for yourself in the chart below. Each device we tested scored around 35 decibels on the low setting, but we saw a bigger difference on the medium and high settings.
Energy consumption
If you’re like me and your allergies are your worst enemy, you’d love to have your air purifier running all the time. The only concern is that your energy bill will definitely go up, but by how much?
To answer this question, we’ll use a device called a Kill-a-Watt and measure how much power each air purifier uses at different fan speeds. From there, we can correlate this to the average monthly cost of running the unit non-stop. All you need to know is the energy cost per kilowatt hour in your state. The following formula describes it best:
The average cost to run an air purifier non-stop for a month = wattage used/1000 * 24 hours * 30 days * average energy cost per kWh in your state.
The chart below shows how much it costs to run each air purifier we tested on high for an entire month in different states with different energy rates.
