The Coway Airmega 400 is a large-room air purifier built for spacious living areas, open-concept spaces, and primary bedrooms. It uses a three-stage filtration system that combines washable pre-filters, pelletized activated carbon, and HEPA filtration, running separate filter assemblies on each side of the unit. A built-in particle sensor feeds into Smart mode, which adjusts the fan speed automatically based on current air quality. However, despite its premium positioning, it lacks Wi-Fi connectivity and smartphone app support, with all controls accessible directly on the unit.
Our Verdict
The Coway Airmega 400 is an excellent choice for pet owners. It efficiently clears airborne dander and allergens from the air, and its high airflow keeps it effective even in larger rooms. If you have a heavy shedder or do any grooming indoors, that extra capacity helps catch fur and dander before it has a chance to settle or spread around the home. It also stays reasonably quiet at lower fan speeds, so it's less likely to bother noise-sensitive cats or dogs during day-to-day use.
High CADR makes it well suited for larger spaces.
Quiet operation at lower fan speeds.
Bulky design takes up a lot of floor space.
The Coway Airmega 400 is an excellent option for bedrooms. Its quiet operation and dedicated Sleep mode make it easy to run overnight, while the built-in air quality sensor can automatically adjust performance as conditions change. The air quality indicator can also be turned off completely for a darker sleeping environment. However, it lacks Wi-Fi connectivity and smartphone app support, so you'll need to adjust settings directly on the unit unless it's positioned within easy reach of your bed. The unit itself is also quite bulky, so if you are working with limited space or a smaller bedroom, it might be a tight fit.
High CADR makes it well suited for larger spaces.
Quiet operation at lower fan speeds.
Dedicated Sleep mode for overnight use.
No Wi-Fi connectivity or smartphone app support.
Bulky design takes up a lot of floor space.
The Coway Airmega 400's particle filtration rate is amazing. Whether it's placed in a large primary bedroom, a spacious living room, a larger kitchen, or an open-concept main floor, its high clean air delivery rate (CADR) gives it the coverage needed to maintain good air quality throughout the space. Even when dialed back to lower fan speeds, its CADR remains high enough to provide meaningful coverage in medium- to large-sized rooms.
High CADR makes it well suited for larger spaces.
High CADR makes it well suited for larger spaces.
Changelog
- Updated Jul 16, 2026: We've updated this review to Test Bench 1.3.1, which adds an additional field to indicate whether an air purifier's filtration system is HEPA-certified. To read more about the changes, see the changelog.
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Updated Jun 25, 2026:
We added a link to the newly reviewed Winix C909 in the Display and Control section of the review for users seeking an alternative with Wifi connectivity and app control.
- Updated Jun 18, 2026: We've updated this review to Test Bench 1.3, which adds a new 'Footprint' test that's meant to score an air purifier's dimensions. If you're interested in learning more about why we made this change, read our changelog article.
- Updated Jun 17, 2026: Review published.
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Differences Between Sizes And Variants
The Coway Airmega 400 comes in two color variants: 'White' and 'Graphite.' We tested the 'Graphite' model, though we expect the other variants to deliver similar overall performance. You can see the label of the unit we bought and tested.
If you encounter another variant of this device, let us know in the comments, and we'll update our review.
Popular Air Purifier Comparisons
The Coway Airmega 400 is a premium air purifier built around strong air-cleaning performance in larger spaces. Compared to the more affordably priced Levoit Core 600S, the Airmega 400 holds up well in air-cleaning performance, though it gives up some ground in convenience. Features like smartphone app control, voice assistant support, and scheduling are missing here, which feels like an odd omission at this price point. The Airmega 400 also compares favorably to the high-end Dyson Purifier Big+Quiet Formaldehyde BP04, delivering stronger air-cleaning performance and coverage. That said, the Dyson offers a more polished overall experience with app connectivity, a remote control, and more detailed air quality reporting. The Blueair Blue Signature Large takes a different approach entirely, pairing solid air-cleaning performance with a furniture-inspired design that lets it double as a side table, making it a easier fit for living spaces where the Coway's more utilitarian look might stand out.
If you're interested in alternatives, check out our recommendations for the best air purifiers, the best air purifiers for pets, and the best air purifiers for bedrooms.
The Blueair Blue Signature Large is a better air purifier than the Coway Airmega 400, though the gap between them is fairly small. The Blueair delivers somewhat stronger particle filtration, holds onto more of that performance at quieter fan speeds, and is quieter overall. It also adds smartphone app connectivity and a more considered design, with a furniture-inspired form factor that lets it double as a small side table and blend into a living room or bedroom more naturally than the Coway. Unlike the Blueair, which relies in part on HEPASilent ionization to achieve its performance numbers, the Coway uses purely mechanical filtration and doesn't produce ozone as a byproduct, making it a better choice if you or your pets are sensitive to ozone.
The Coway Airmega 400 is a better air purifier than the Winix C909. The Coway delivers stronger particle filtration performance and significantly higher airflow, making it the better choice for very large living rooms, open-concept spaces, and other expansive areas. It also uses pelletized activated carbon rather than a thin carbon sheet, which should give it an advantage in odor reduction. The Winix counters with Wi-Fi connectivity, remote app control, scheduling, and air quality monitoring, all of which are missing on the standard Airmega 400.
The Coway Airmega 400 is a better air purifier overall than the Levoit Core 600S, though the Levoit remains a compelling alternative at a much lower price. Both units deliver excellent air-cleaning performance in larger spaces, but the Coway pulls ahead with stronger particle filtration and quieter operation. The Levoit counters with a more modern feature set, including smartphone app connectivity, voice assistant support, scheduling, and remote air quality monitoring, all of which are absent on the Coway.
The Coway Airmega 400 is a slightly better air purifier overall than the NuWave OxyPure, though the two are closely matched on air-cleaning performance. Both are built for larger spaces and deliver excellent particle filtration, but the Coway edges ahead with stronger overall filtration and quieter operation. The NuWave is a compelling alternative, particularly in terms of cost. Its filtration system is unusual in that it relies largely on washable filters with an advertised lifespan of up to 20 years, which can make it significantly cheaper to run over time compared to the Airmega 400's two replaceable cartridges that Coway recommends swapping out annually. The NuWave also adds smartphone app connectivity and a broader range of operating modes.
Test Results
The Coway Airmega 400's top-mounted control panel provides access to three fan speed settings, along with a timer function, Sleep mode, and Smart mode, which automatically adjusts fan speed based on readings from the built-in air quality sensor. The unit also features separate filter maintenance indicators, with a Wash reminder for the pre-filters and a change reminder for the Max2 filters, so you won't have to guess when maintenance is required.
A color-coded air quality indicator provides a quick visual overview of current air quality:
- Blue: Good
- Purple: Moderate
- Pink: Unhealthy
- Red: Very Unhealthy
Its illumination can be turned off completely for use in bedrooms or other dark environments. When operating in Smart mode, the Airmega 400's light sensor can also automatically switch the unit into Sleep mode after detecting darkness for several minutes, helping reduce both noise and light levels overnight.
One notable omission is app connectivity. While the nearly identical Airmega 400S, or alternatives like the Winix C909, can be controlled remotely through Coway's companion app, the standard Airmega 400 tested here lacks Wi-Fi support, meaning all adjustments must be made directly on the unit.
The Coway Airmega 400 uses a three-stage filtration system made up of a washable pre-filter, a pelletized activated carbon filter, and a HEPA filter. Unlike many air purifiers, it runs two complete filter assemblies at once, with each side of the unit housing its own pre-filter and Max2 filter cartridge.
The washable pre-filters serve as the first line of defense against larger contaminants such as dust, lint, hair, and pet fur. Behind them sit Coway's Max2 filters, which combine pelletized activated carbon and HEPA filtration into a single replaceable cartridge. The HEPA portion is designed to capture fine airborne particles such as pollen, dust, smoke, and pet dander, while the activated carbon section is intended to reduce odors and gaseous pollutants. The use of pelletized activated carbon is a notable advantage over the thin carbon layers found in many competing air purifiers. However, meaningful odor reduction typically requires a substantial amount of activated carbon. You can read more about activated carbon filtration in our air purifier performance research.
Coway recommends cleaning the pre-filters regularly and replacing the Max2 cartridges roughly once a year. Since the Airmega 400 uses two cartridges at once, replacement costs are higher than you'd pay for a smaller single-filter unit, though that comes with the territory given its larger size and higher airflow capacity. Replacement filters can be purchased directly from Coway.
This unit's maximum clean air delivery rate is excellent. At its highest fan speed, it has the airflow needed to keep large primary bedrooms, spacious living rooms, and open-concept areas feeling noticeably cleaner. It's also well-suited for quickly clearing the air after activities like cooking, vacuuming, or opening windows during periods of poor outdoor air quality.
This air purifier does a good job of maintaining cleaner air while operating at a comfortable noise level. It moves enough air to effectively handle bedrooms, home offices, and many living spaces without becoming a constant distraction, making it easy to leave running throughout the day or overnight. While higher fan speeds provide faster air cleaning, its quieter settings still deliver enough performance to keep up with everyday airborne particles in most situations.
This air purifier is impressively quiet overall. At its lowest fan speed, the operating noise is barely above a whisper, making it well-suited for overnight use in a bedroom or anywhere else where background noise is a concern. Higher fan speeds produce a noticeable increase in noise, though they remain reasonably unobtrusive for most people. At its highest setting, it gets considerably louder, roughly comparable to the hum of a window air conditioner, and may start to become a distraction if you're sitting or working nearby.