In order to help inform our air purifier picks, we gathered 14 of the most popular models out there at the CNET Labs product testing facility in Louisville, Kentucky, where we put them through the same rigorous set of tests. Working with trusty lab associate Eric Snyder, our goal was to determine which air purifiers offered the best performance in terms of particle removal efficiency, energy consumption and quietness, while also evaluating their respective feature sets and value. Tag along as we unveil 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’d bear witness to a universe of tiny fragments floating around and being carried by the wind. But what is that stuff, anyway?
In truth, it’s a combination of anthropogenic (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. We are, at all times, breathing in a mixture of it all.
According to the US Environmental Protection Agency, 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. PM10 and PM2.5, which are particles of less than 10 and 2.5 micrometers in diameter, respectively, pose the greatest risk to human health since once inhaled, they allocate deep into the lungs and even into the bloodstream, impairing the proper functionality of the lungs and heart.
Air purifiers are supposed to help us improve indoor air quality conditions by removing these types of particles from the air — but how well do they do that? That’s where our CNET Labs team comes in. Put simply, our mission was to create an environment in which we exposed each air purifier unit to particle-saturated air of roughly the same concentration in order to assess how quickly and efficiently they get the air back to breathable conditions.
To achieve this, we needed to find a way to produce a quantifiable and fairly repeatable amount of particles; an environment or “test chamber” in which these particles and the air purifier units would be contained; and an accurate particle counter that acts as our control device and allows us to visualize this data. Here’s what we came up with:
Custom made smoke bombs, which are made of 50% potassium nitrate (KNO3), 40% sucrose (sugar) and 10% sodium bicarbonate (baking soda), and a safety fuse for safe ignition at a distance. The sugar acts as our fuel source, while the potassium nitrate acts as an oxidizing agent and the baking soda ensures that our dry mixture sustains a slow and even burn.
Our air purifier test chamber, designed and built by Eric and myself. Its features include a clear-view front panel made of plexiglass, a gloved hand access on the right, which allows us to manipulate the air purifiers, a particle counter holder for our control device, two fans that ensure proper mixing of the air and smoke inside the chamber, vent ports that ensure there is a small amount of fresh air at all times, an ignition port to light up the smoke bombs from outside the rig, and an exhaust port that removes the remaining smoke safely from the chamber and the building after each test. The chamber is not hermetically sealed, but it’s tight enough to ensure that no hazardous amount of smoke escapes to the surroundings.
Using the Temtop PMD331 Particle Counter, we were able to verify that only 5 grams of our smoke bomb dry mixture produces roughly between 590 million 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. Even though we’re able to count particles of different sizes individually, it’s the total number of particles we care about. That is, the sum of all particles of different sizes.
Having figured out the essentials, our testing procedure is carried out 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 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 Temtop allows us to accurately track the impact that the air purifier has on the particle count in real-time.
Under normal conditions — that is, when there was no smoke in the test chamber — the total particle count reported by the Temtop was around the 10 million mark, so think about this as the “finish line” for this particle removal race. In our test logic, the faster the air purifier gets the particle count back below 10 million particles per meter cubed, the better. We carry out this test twice for each air purifier, one at the lowest fan setting and another at the highest fan setting to visualize the range of operation of each unit. Check out the results for each unit we tested at both low and high fan settings in the GIFs below:
The noise level test
This is a simple test, but one that’s telling. 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 in your bedroom and leaving it running through the night without disrupting your sleep.
We perform this test in our sound-enhancing studio to make sure that the decibel meter picks up only soundwave stimuli from the air purifiers, excluding other possible sources. The lower this number, the quieter the air purifier runs. You can see the results for yourself in the graph below — each unit we tested clocked in at around 35 decibels at its low setting, but we saw greater differentiation at medium and high settings.
If you’re like me and your allergies are your worst enemy, you’d prefer it if your air purifier is running all the time. The only concern is that your energy bill will definitely increase. But by how much?
To answer this question, we use a device called Kill-a-Watt and measure how much power each air purifier consumes at different fan settings. From there, we can correlate this to an average monthly cost of running the unit nonstop. All you need to know is the energy cost per Kilowatt-hour in your state. The following formula describes it best:
average cost to run an air purifier nonstop for a month = watts consumed/1000 * 24 hours * 30 days * average utility cost per KWh in your state
The chart below shows how much each air purifier we tested would cost to run for an entire month at its high fan setting in a variety of states with different energy rates.