Our verdict: The Coway Airmega 400S ranks 9th of the 10 air purifiers we compare, with 8.4 out of 10.
Coway Airmega 400S
8.4/10
The Coway Airmega 400S is a large, app-connected air purifier for open-plan living areas and very big rooms. It suits shoppers who want strong smoke, dust and pollen cleaning and will accept a heavy unit and pricey filters.
CADR of 328 smoke, 328 dust and 400 pollen, rated by Coway for up to 1,560 square feet at two air changes per hour
Two HEPA filters and two washable pre-filters for heavy-duty cleaning
Auto, eco and sleep modes, with noise from about 22 dB
Wi-Fi app control, plus an air quality monitor and filter indicator on the front
Keep in mind
Weighs about 25 pounds and is wide at the base
Two Max2 filters make replacement costly
Why the Coway Airmega 400S scores 8.4
Each bar shows where it places among the 10 air purifiers in this guide, so a full bar is 1st of 10. How happy owners are counts for most of the score.
How happy owners are7th of 10
How many rated it8th of 10
How new it is8th of 10
Why it sits behind the IQAir HealthPro Plus XE HyperHEPA
The IQAir HealthPro Plus XE HyperHEPA (8.5) beats the Coway Airmega 400S (8.4) because it is the newer design. The Coway Airmega 400S leaves owners a little happier, but not by enough to close the gap.
About the Coway Airmega 400S
The 400S is a tall, square tower with a Max2 filter on each side. Each Max2 filter combines activated carbon with True HEPA, and each is paired with a washable pre-filter, so the unit holds four filters in total. Coway rates it at 328 CADR for smoke and dust and 400 for pollen. That covers up to 1,560 square feet at two air changes per hour with 8-foot ceilings.
It has five fan settings (Smart, Sleep, Low, Medium and High) and a 1, 2, 4 or 8 hour timer. In Smart mode a built-in sensor raises or lowers the fan as the air changes, for example when you cook. A colored ring on the front shows air quality, and the filter indicators sit beside it. The ring and lights can be turned off, which the Coway IoCare app can also do.
The app works over Wi-Fi and with Alexa and Google Home. It shows indoor and outdoor air quality, filter life and fan speed, and it supports schedules and 24-hour, 7-day and 30-day history. One reviewer found it mostly duplicated the controls on the unit itself. It comes in black or white.
What owners report about the Coway Airmega 400S
We found very little owner feedback we could confirm for this exact model, so what follows comes mainly from published reviewers, not owner threads.
Reviewers praise how thoroughly it cleans, including smoke and odors, and say Sleep mode and Low are close to silent. Medium and High are audible but sit in the background. The main complaint is the cost of replacement filters. The reviewers also found the app useful for alerts but largely redundant with the controls on the unit.
One reviewer with a dusty home and a dog washed the pre-filters about every eight weeks. Reviewers disagree on how often the Max2 filters need replacing, from about once a year to every three to six months, so budget for the shorter end if the air is dirty.
Who the Coway Airmega 400S suits
Buy it for a large living room, an open-plan floor or a room where smoke, pet dander or pollen is a problem, and where you want automatic fan control. It is a big unit, so it needs floor space and is awkward to carry between rooms.
Look elsewhere if filter running costs matter most: the Shark NeverChange Air Purifier HP152 is built around a long-lasting filter. For a bedroom or a small room, the Levoit Core 300S-P is smaller and quieter in practice, and the Coway Airmega Mighty AP-1512HH suits rooms around 360 square feet.
Questions about the Coway Airmega 400S
How often do you replace the Coway Airmega 400S filters?
Sources differ. One reviewer expected about a year, while another said every three to six months. The Max2 filters are sold as a pair and the pre-filters are washable, so check the unit's filter indicator.
What does the wash light mean on the Coway Airmega 400S?
It means the pre-filters need washing. The rings around the filter buttons fade as the filters get dirty. When a ring goes fully dark, the pre-filter and filter icons light up. Rinse or vacuum the pre-filter and let it dry fully before putting it back.
Does the Coway Airmega 400S remove odors?
Yes, to a degree. The Max2 filters include activated carbon, and one reviewer found it reduced odors better than most large purifiers, though a slight smell lingered in their test.
How loud is the Coway Airmega 400S?
Quiet on low and in Sleep mode, from about 22 dB. One reviewer measured the top speed at 43.2 dB and described it as background noise.
How big a room does the Coway Airmega 400S cover?
Coway rates it for up to 1,560 square feet, at two air changes per hour with 8-foot ceilings. A reviewer of the larger-room use case suggested its practical sweet spot is smaller than the rating.
Other air purifier picks
The other badge winners in our air purifiers ranking.
Every score here comes from our ranking model; no editor sets the order. Too few review sites cover air purifiers for their verdicts to lead, so this ranking is led by owners. It ranks products by how happy owners are, holding back any product few owners have rated until more agree. How many rated it and how new it is only settle close calls, and value for money earns its own badge rather than a higher place. We compared 20 models for this guide before settling on these ten.
Brands can't pay to be included or to move up. We last checked these picks in October 2026.
