What every best Air Purifiers has:
- HEPA filtration.
- High maximum air-exchange rate.
- Filter-change alert.
Clears out big rooms. If you want an air purifier for big rooms, or if you live near a highway or have especially questionable air for other reasons, reviews point to the Coway Airmega 300 as a good choice. ConsumerReports.org gives it a middling grade overall, but does say that at high speeds, it does an excellent job of clearing a room of dust, smoke, and pollen, although it's not all that effective at low speeds. That said, in testing at TheSweethome.com, John Holecek and Tim Heffernan find that Airmega will keep smaller spaces exceptionally clean even on the lowest setting. It's the third best at reducing airborne particulates in that site's tests, "87 percent reduction (not statistically different from the Mighty's 88 percent) in particulate levels over 20 minutes versus the original measurement."
Very smart. The Airmega 300 includes a "smart" auto mode that monitors the air quality and adjusts the air speed accordingly. There's also an eco mode that will conserve energy by turning the unit off altogether if no pollution is detected at all for 10 minutes, and a sleep mode that will do the same after three. There's an indicator that will tell you when the filters need changing, (in the case of the main filter) or washing (in the case of the pre-filter). A ring indicator on the front changes color to inform you of the room's air quality. The unit is on the large side, measuring 21.2 by 13.6 by 13.6 inches, and a bit heavy (at 21.4 pounds) and there are no casters to make moving it about easier. There's also a step up version, Conway Airmega 300s (Est. $585), which adds Wi-Fi connectivity and an app that lets you schedule operation and monitor the air quality in a room remotely, but the added features don't do particularly well in reviews, so our advice is to stick to the base 300, which cleans the air just as effectively, and costs less.
Loud on high. Like all air purifiers, the noise levels at higher speeds is hard to ignore, though ConsumerReports.org says that it's one of the quieter air purifiers it tested at high speed, many sleepers will likely still find it to be a bit too loud. At low speeds, the unit draws good comments for not disturbing the peace when talking or sleeping. The auto mode helps assure that the unit does not run at high speeds when the air quality does not require it.
High initial cost, low annual cost. ConsumerReports.org estimates the annual cost of ownership (considering both energy usage and filter cost) at $110 per year, which is the second lowest of any large room (350 square feet or larger) unit. TheSweethome.com comes up with somewhat higher estimates, however, pegging the annual cost of electricity at just under $100, while the filters will run you just under $50 per year (based on its test of the Coway 300s, which is identical save for the Wi-Fi feature).
John Holecek and Tim Heffernan test the Coway Airmega 300s, and use those conclusions to recommend the more basic Airmega 300 (which lacks Wi-Fi connectivity and a proprietary mobile app but is mechanically identical) for large rooms and situations where the air is particularly dirty. "With a pair of filters, the Coway Airmega 300 is rated to clear spaces as large as 1,250 square feet and will keep smaller spaces exceptionally clean even on the lowest setting," they say.
Editors here test more than 30 room-size air purifiers, including the Coway Airmega 300. Testers rate the units' ability to clear a sealed chamber of dust, pollen and smoke (on low and high speeds) and rate their measured noise levels on both speeds. Annual energy and filter costs are also estimated.
User reviews for the Airmega 300 are limited, but we found nearly 50 of them at Amazon.com. Most are pleased with performance and usability, and the unit earns a score of 4 stars thus far. A few owners received a defective unit, or claimed that air purifier didn't perform satisfactorily, but most give it better than 4 stars.