Large spaces are the Coway Airmega 400S's job, and it cleans up to 3,120 sq. ft. quickly while staying quiet in sleep mode. Air cleaning performance is the strength, and the smart controls are genuinely convenient. The drawbacks worth weighing before buying: high operating costs and a large physical footprint.
Full review
328 CFM rated for 3,120 square feet
The 400S is sized for rooms most purifiers cannot handle. Its clean air delivery rate is 328 CFM for smoke and dust, which Coway translates into 3,120 square feet at one air change per hour, or 1,560 square feet at two. TechGearLab, which scored it 75 out of 100, measured the practical version of that claim: particulate counts falling from around 500 on the air-quality index to almost nothing in 45 minutes. On an open-plan floor that is the difference between a purifier that keeps up and one that is decoration.
Two carbon layers ahead of the HEPA stage
The HyperCaptive stack runs a washable pre-filter, an activated carbon layer and a HEPA filter on each of two intake faces. The doubled carbon is what separates this from cheaper units on smells rather than dust, since gases and volatile compounds pass straight through HEPA media. TechGearLab still found a faint acrid note lingering after an hour of simulated smoke, so treat odour removal as strong rather than absolute.
22 decibels in sleep mode, 24.7 pounds on the floor
On low speeds the unit is genuinely quiet, dropping to 22 decibels in sleep mode, which is below a refrigerator hum and easy to leave running overnight. High speed is audible, as it has to be to move that much air.
The physical cost is size. At 22.8 inches tall and 24.7 pounds this is furniture rather than an appliance you tuck behind a chair, and it needs clearance on both sides because it draws air through two faces. The matte finish resists fingerprints, which helps, but nothing disguises the footprint.
A built-in sensor worth treating sceptically
The smart half works through the IoCare app plus Alexa or Google Assistant, with scheduling and remote control. Air Purification Education is direct about the limitation: the built-in air-quality sensor should be taken with a pinch of salt, as consumer-grade particle sensors generally should, and that undermines the automatic mode which depends on it. Running a fixed fan speed is the more predictable approach.
$749 up front and expensive filters afterwards
TechGearLab scores operating cost low, and that is the real objection. Replacement filters are expensive, the unit draws more power on high than smaller competitors, and Breathe Quality notes that the roughly $749 sticker puts it against premium brands rather than mid-range ones. Filters last up to twelve months, which softens the blow without removing it.
Strengths
- +Covers spaces up to 3,120 sq. ft. with high efficiency, per TechGearLab
- +Removes 100% of particulates in 45 minutes, according to TechGearLab
- +Operates at whisper-quiet 22 dB in sleep mode, per Breathe Quality
- +Features smart mode that auto-adjusts based on real-time air quality sensors
Watch-outs
- −High operating cost due to expensive replacement filters
- −Bulky dimensions (14.8" x 22.8" x 14.8") occupy significant floor space, as Breathe Quality notes
- −Requires a mobile app to access certain smart features
How it compares
The Coway Airmega 400S dominates in raw coverage power, cleaning spaces up to 3,120 sq. ft., which far exceeds the 540 sq. ft. limit of the Blueair Blue Pure 211+ and the 99 sq. ft. limit of the Dyson TP07. While it shares smart features with the Levoit Core 400S, the Coway is physically much bulkier and incurs higher long-term filter costs than the Levoit.
Price history
3 daily reads from cowaymega.com since Oct 29, 2026. Lowest $749 (Oct 31), highest $749 (Oct 31), latest $749 (Nov 4). We call whether it's a good price once there are 7 days of reads at one store.
Rating sources
Counts as 4.24/5 in our score — this publisher's 138 scores on the site average 3.66, so its scores are adjusted up to compare fairly with other publishers.
Counts as 4.69/5 in our score — this publisher's 1 scores on the site average 4.80, so its scores are adjusted down to compare fairly with other publishers.
Our 4.5 score is the average of the 2 scored reviews above, each adjusted for how strictly its publisher scores; 1 more reviewed it without printing a score and is not in the average. More about methodology.
