How We Tested
Hi, I’m Julia MacDougall, the Senior Scientist here at Reviewed. I’ve tested a wide variety of products, including paper shredders, backpacks, and coding toys for kids.
I have allergies that follow me around wherever I go. My friends know that if they don’t see me flash a packet of tissues at least once while I’m out, chances are I’ve been replaced by an allergy-free clone. Naturally, I was hyped to test out air purifiers because I was curious to see if they really work.
The Testing Area
To test these devices in Reviewed’s lab, I built an airtight 200-square-feet space to mimic the size of large rooms, like a bedroom or living room.
To begin testing, I set off a red smoke grenade to see if the air purifier could clear the room (spoiler alert: it can, but it completely clogs the filters), and as a result, the room’s walls were slightly red-tinged from then on, looking like a scene out of Dexter.
The room replicates the way someone might use an air purifier in their home, and without having to worry about external air currents or smells interfering with our tests.
I tested air purifiers for casual usage and whether it could eliminate odor. I asked volunteers to take two units home and use each for two weeks at a time. Volunteers then filled out surveys focused on user-friendliness and their impressions on how each unit worked in their homes.
The smell tests were conducted in the testing room I built by introducing a smell (cigarette smoke, fish oil, essential oils) into the sealed room for 20 minutes, running the air purifier on its highest fan speed setting for four hours, and then asking people to identify what they smelled.
The more smell confusion recorded, the better the air purifier performed at removing a particular odor from the room.
Unfortunately, we were unable to measure the size and type of particulates in a room before and after using an air purifier. (If you want that information, check out the guides from our friends at the Wirecutter and Consumer Reports).
However, we’re confident in our testing, because it allows us to replicate the experience someone actually using the air purifier in his or her home would have, since air particulate differences detected by machines are not necessarily detectable by humans.
What is a HEPA Air Purifier?
Similar to space heaters and air conditioners, air purifiers draw air in using a series of fans, then condition the air in some fashion, and finally blows the air back out into the room. Inside the unit, a HEPA filter removes particles so the air blowing out is cleaner than what came in.
While there are many types of air filters these devices use, and sometimes in combination with each other, HEPA filters, are known to be the most effective. These filters are often highly folded and made up of a bunch of fibers that have been forced together at a bunch of different angles so as to increase the likelihood of catching a particle, large or small, and removing it from the air.
While the EPA says there’s no widely accepted definition of HEPA performance in consumer products, a “True HEPA” air purifier is known to be the most effective.
The most common HEPA-related marketing claims you’ll see from manufacturers include:
True HEPA filters which have the highest efficiency rate of filtering out air pollutants, at 99.97 percent.
HEPA filters generally have a 99 percent efficiency rate.
HEPA-like/99% HEPA/HEPA-type/HEPA-style filters are filters that are less effective and not considered pure HEPA filters.
What Does the Clean Air Delivery Rate (CADR) Mean?
While researching these appliances you’ll often see a CADR rating mentioned. The Clean Air Delivery Rate (CADR), unlike the HEPA filtration system, is determined and verified by an independent testing lab using AHAM standard AC-1.
The CADR values measure how quickly a given air purifier can reduce the amount of dust, pollen, and smoke in a room to levels that would be equivalent to adding completely clean, uncontaminated air to the same space.
Look for higher CADR ratings to guide your eye, but again, don’t let it make your break your purchasing decision. Be aware that the CADR value is an ideal value, and know that your typical CADR rating may be lower than the number on the air purifier’s box.
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We use standardized and scientific testing methods to scrutinize every product and provide you with objectively accurate results. If you’ve found different results in your own research, email us and we’ll compare notes. If it looks substantial, we’ll gladly re-test a product to try and reproduce these results. After all, peer reviews are a critical part of any scientific process.
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