How did we find the best air purifier? First you evaluate thousands of online user reviews to find the most well regarded models. Then you buy those models, seal up a room so it's airtight, burn enough paper and incense to make that room look like a Cheech and Chong movie, then you stick the air purifiers in that room and see how they fare. Well, that's the short version. Read on for the nitty gritty details of how we conducted our controlled, comparative tests.
Air Cleaning Performance
Obviously air cleaning performance is the most important factor for air purifiers, so we made sure our testing was pushed these devices to their limits. We chose a 150 square foot room for our testing, and sealed up the windows and doors to make sure no outside air flow would affect our results. We placed a Dylos air quality meter on a 2 foot high bench 3 feet from the center of the room. We then burned incense and paper until the small particle reading (the harder particles to filter) was between 1300 and 1500. We then placed each purifier, one by one, in the center of the room and ran them for an hour on their highest settings. The Dylos provided a reading history so we could track the effect the purifiers had on airborne particulate concentration over time. We Awarded scores based on both how quickly each model removed airborne particles, and the lowest concentrations they were able to maintain.
We chose smoke for our test because it produces a lot of particles in the 0.3 micron size range. This is the most difficult size of particle to filter out. Larger particles are easily trapped in filters, while smaller particles are actually so small that they tend to get caught up in the pores and irregularities of the fibers that make up filters. 0.3 microns is right in the sweet spot where particles can fit between the filter fibers but are too large to get trapped in the fiber pores. Thus this size presents the most difficult task, and thus the most difficult test, for an air purifier.
We've found that noise is somewhat subjective. We always measure the noise produced by our testing products with a decibel meter, but we often find that the obtrusiveness of a noise depends more on the pitch and timbre of a noise rather than its volume. Air purifiers were no exception. Thus for our noise testing we ran all model on low, medium, and high settings and subjectively rated how annoying and noticeable the noise was.
Ease of Use
Here again we applied a thorough, subjective rating system. We adjusted every setting on each model using both the on device controls and remote control (if one was included) to test their user interface. We also replaced the filters in each model multiple times, and moved each model all over the office to assess how portable they were. We combined all of these aspects to arrive at our ease of use scores.
Our operating cost scores were based off of an estimated lifetime cost figure. This figure took three things into account: cost of the purifier, the amount of electricity each purifier uses, and how much replacement filters cost. In this calculation we assumed that each purifier would last for five years, that they would be run for 12 hours a day, that most electricity cost are around the national average ($0.12/kWh), and that filters would be replaced according to manufacturer recommendations. We used a Kill A Watt Meter to measure how much electricity each device used over the course of two hours to determine average energy usage. Our final estimated lifetime cost figures ranged from $143 to $1,105.