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Coway Airmega 400S Review

A high-performance, high-volume machine that has user-friendly interface options and a wider range of controls than other purifiers of its class
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Coway Airmega 400S Review (The Coway Airmega 400S is a workhorse for large spaces. It has a nice finish, too, and keeps noise to a minimum.)
The Coway Airmega 400S is a workhorse for large spaces. It has a nice finish, too, and keeps noise to a minimum.
Credit: Abriah Wofford
Price:  $749 List
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Manufacturer:   Coway
By Genaveve Bradshaw, Nick Miley, and Ryan White  ⋅  Oct 25, 2024
75
OVERALL
SCORE


RANKED
#8 of 11
  • Air Cleaning Performance - 40% 9.5
  • Noise - 30% 7.1
  • Ease of Use - 20% 6.4
  • Operating Cost - 10% 2.6

Our Verdict

If you're looking for an air purifier that can filter a lot of air without roaring like a jet engine, the Coway Airmega 400S is a great option. This relatively inexpensive unit is easy to use, featuring both an on-unit and app-enabled user interface, and boasts a nice exterior design. The unit also has an air sensor that informs the “smart mode,” which turns the filter on and off depending on air quality. Most importantly, the filter is among the highest-rated for air cleaning performance, making it a go-to choice for those with airborne particulate sensitivities. The two main considerations for this model, in our opinion, are the overall high operating cost and the space it occupies. If you can handle these drawbacks, it remains a good choice.
REASONS TO BUY
Excels in large spaces
Powerful purifying
Extensive control options
Great noise to power ratio
REASONS TO AVOID
High operating cost
Bulky
App required for some features
Hefty investment
See how it measures up versus competitors in our article on the best air purifiers.

Compare to Similar Products

 
coway airmega 400s
This Product
Coway Airmega 400S
Awards Top Pick Award
Best for Larger Rooms
Editors' Choice Award
Best High-End Air Purifier
Editors' Choice Award
Best Air Purifier for Most
Best Buy Award
Best Value for a Smart Air Purifier
Best Buy Award
Best Value for Small Rooms
Price $749 List
$529.00 at Amazon
$468 List
$426.18 at Amazon
$230 List
$229.99 at Amazon
$220 List
$219.99 at Amazon
$100 List
Check Price at Amazon
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Bottom Line A top-end purifier that excels in larger areas while offering users a greater degree of control both on the unit and via the proprietary appThis purifier can clean with the best of them and we can't recommend it enough for those who can afford itIt's tough to find an air purifier that can do it all, but rest assured that this one canThis app-compatible model is user-friendly and comes with an assortment of programmable featuresAn affordable, high performing option that is ideal for smaller spaces
Rating Categories Coway Airmega 400S Alen BreatheSmart 45i Coway Airmega 1512HH Levoit Core 400S Levoit Core 300
Air Cleaning Performance (40%)
9.5
9.1
8.3
9.4
7.8
Noise (30%)
7.1
7.3
7.6
6.8
7.0
Ease of Use (20%)
6.4
8.9
8.3
7.9
7.4
Operating Cost (10%)
2.6
6.1
8.3
6.7
7.8
Specs Coway Airmega 400S Alen BreatheSmart 45i Coway Airmega 1512HH Levoit Core 400S Levoit Core 300
Measured Annual Cost $271.28 $178.96 $110.16 $148.14 $96.81
Airborne Particulate Reduction After 1 Hour (%) 100.00% 99.98% 100.00% 100.00% 99.92%
CADR 328 (Smoke)
328 (Dust)
400 (Pollen)
245 overall
139.9 (Smoke)
207.9 (Dust)
230.4 (Pollen)
234 (Smoke)
248 (Dust)
232 (Pollen)
Sleep: 59
Speed 1: 88
Speed 2: 118
Speed 3: 177
Speed 4: 260

*Per Levoit, their stated CADR ratings for this product are the same for Smoke, Dust, and Pollen but differ for fan speeds
141 (Smoke)
140 (Dust)
145 (Pollen)
Measured Dimensions 14.8" x 14.8" x 22.8" 8.5" x 15.0" x 25.0" 9.6" x 16.8" x 18.3" 10.8" x 10.8" x 20.5" 8.7" x 8.7" x 14.2"
Measured Weight 24.6 Ibs 15.5 Ibs 13.1 lbs 10.4 Ibs 7.3 Ibs
Measured Cord Length 7' 7' 8" 6' 6" 6' 3" 6' 3"
True HEPA (99.97%) Yes Yes Yes No No
Estimated Lifetime Cost (5 years) $1,356.42 $894.81 $550.81 $740.70 $484.03
App Control Yes Yes No Yes No
Air Quality Sensor Yes Yes Yes Yes No
Measured Decibels 51.2 48.3 55.9 51.8 52.3
Energy Star Certified Yes Yes Yes Yes Yes
Listed Coverage 3,120 sq. ft 1600 sq. ft 1,748 sq. ft 1560 sq. ft 219 sq. ft

Our Analysis and Test Results

The main draw for the Coway Airmega 400S is the unbridled power it possesses. It'll be really tough to find another air purifier that can outdo this one in terms of pure performance. It has incredible coverage and should prove adequate in nearly any space up to about 3,120 square feet. Continue reading to find out just how well it did in our comprehensive testing process.

Performance Comparison


The Coway Airmega 400S is a big appliance, but it also cleans at a high level.
Credit: Natalie Kafader

Air Cleaning Performance


The Coway Airmega 400S is a class leader in our air cleaning performance analysis. Few models can filter air as thoroughly and at such a high rate while at the same time reducing odors such as smoke in the process. Not surprisingly, this unit has one of the highest Clean Air Delivery Rates (CADR) in its class which was supported by our independent assessment using a Dylos air quality monitor.


Our analysis of air cleaning performance is simple yet sophisticated and comprehensive. We burned sheets of paper in a tin-foil-lined bowl to bring the Dylos Air Quality Meter particulate reading to approximately 500 AQI (around 35,000 large particles). We then turned on the purifier and recorded the time it took to clean the air. The 400S reduced the particulates to 49 in 30 minutes and down to an impressive two particles in 45 minutes. The 400S also has a robust CADR. While many manufacturers list the CADR in a single number, the 400S breaks this rating into three relevant categories. These categories and their ratings (in cubic feet) are as follows: smoke (328), dust (328), and pollen (400). All told, the Airmega 400S removed 100% of particulates in the allotted 60 minutes.

coway airmega 400s - the airmega 400s cleaned our simulated smoky environment quickly...
The Airmega 400S cleaned our simulated smoky environment quickly, removing 100% of particulates in just 45 minutes.
Credit: Natalie Kafader

Another key component of air cleaning performance assessment is the odor reduction analysis. Burned paper used in this evaluation produces small molecules that are the source of the perceived smell. Removing these molecules from the air is quite difficult as they are often too small to be captured by the purifier's filter. Despite the difficulty of this task, the 400S did quite a bit better than other models in the class, though there was still a slight acrid smell left behind in the room at the end of the hour-long testing interval.

As a final note on air quality, this unit has a built-in sensor that automatically turns on the machine when air quality falls below a certain threshold. While this feature is not a rated component in this assessment, we thought it was a nice touch worth mentioning.

coway airmega 400s - here, we are logging the aqi of our smoky room.
Here, we are logging the AQI of our smoky room.
Credit: Natalie Kafader

Noise


No one wants to trade air pollution for noise pollution. As such, we assess the volume and pitch of the noise produced by the purifiers under our review. While the Coway Airmega 400S is not the quietest model in the class on high or medium settings, it's ultra quiet on low. Moreover, the pitch is relatively natural and easily goes unnoticed. This assessment is all the more impressive when one considers how much clean air this machine moves and the size of the motor and fan required to do that work.


Our assessment of the noise produced by the air purifiers is measured by a sound pressure monitor (measuring decibels) and our ears. The sound pressure monitor measures the noise produced by the machine at six feet, while our ears assess the pitch of the motor and fan as it's not just the volume but also the kind of noise that is being produced that can be distracting. We assess the machine's volume and pitch at low, medium, and high settings.

coway airmega 400s - coway airmega 400s being tested for its noise output at 6 feet.
Coway Airmega 400S being tested for its noise output at 6 feet.
Credit: Genaveve Bradshaw

The 400S also has a sleep feature. For those who are extremely light sleepers, be aware that this machine kicks into an ultra-quiet “sleep mode” when the room it's in becomes dark and the air quality is sufficiently high. This setting is so low that you can hardly hear it running.

Ease of Use


The two most important things an air purifier does are remove particulates from the air and do so quietly. However, once those aspects are satisfied, the device should also be easy to use. While not the easiest purifier to use in its class, the 400S is not tough to figure out. To evaluate the ease of use we look at the device's setup time, interface (remote and on-unit controls), customization (air-quality sensor and settings), and portability (dimensions, carrying handles, and weight).


Users can control the power, timer, mode, fan speed, and nightlight...
Users can control the power, timer, mode, fan speed, and nightlight via the smart app.
Thanks to the app, you can view the air quality of your home from...
Thanks to the app, you can view the air quality of your home from anywhere.
We love the ability to remotely control this purifier via the companion smart app.

The 400S is a breeze to set up, requiring less than five minutes from boxed-up to fan spinning. The unit also has an app that acts as a remote control. The app is easy to navigate; however, it is largely unnecessary because the onboard controls are well laid out and intuitive, with a touch slider for speed settings and lights indicating both settings and air quality. However, all this is moot because when the unit is set to the “smart” mode, it will turn itself on/off depending on the air quality. Finally, the 400S is on the larger and heavier (24.6 pounds) end of the spectrum for air purifiers in our review. While it isn't advisable to travel with this unit, its carrying handles make it fairly easy to move around the house.

coway airmega 400s - weighing in at a whopping 24.6 pounds, the coway airmega 400s is not...
Weighing in at a whopping 24.6 pounds, the Coway Airmega 400S is not small by any stretch of the imagination.
Credit: Natalie Kafader

Operating Cost


In our operating cost testing, we determine the operating cost of an air purifier by using the national average kilowatt-hour rate of $0.13, and we assume a daily usage of 12 hours per day. We also include the cost of the filter replacement based on the manufacturer's recommendations and the cost of the purifier itself. Finally, we assume a five-year life of the device, so the unit's cost is divided over the first five years.


When it comes to larger appliances — especially those that run for long periods of time — operating costs are a real concern both in terms of maintenance and power consumption. While the power consumption of the Coway Airmega 400S isn't excessive, considering the amount of air the unit can move, its filters come at an eye-popping $129. In the 400S's defense, it does use a true HEPA filter (the gold standard for air purifying filters). However, this defense only goes so far. As such, the long-term cost of this unit is among the highest in the class.

coway airmega 400s - the true hepa filters are pricey to replace.
The true HEPA filters are pricey to replace.
Credit: Natalie Kafader

Should You Buy the Coway Airmega 400S?


Looking at the upfront and long-term cost of the 400S alone, it would be easy to say that this unit offers consumers a poor value. However, for the right user, the cost will pencil out. This unit is great for big spaces and outperforms the competition in this regard. So, if you have a big indoor space that you want to keep particulate-free, this machine will be well worth the high cost.

coway airmega 400s - we recommend the coway airmega 400s for those who want to purify...
We recommend the Coway Airmega 400S for those who want to purify large spaces and don't mind paying a lot for a replacement filter.
Credit: Natalie Kafader

What Other Air Purifiers Should You Consider?


If you want to save money but can't compromise on coverage levels, the Levoit Core 400S is an effective machine and is half the weight. It doesn't use industry-leading HEPA filters, but that didn't stop it from producing great cleaning results. If you don't quite need this level of power but still want good cleaning ability, the Alen BreatheSmart 45i is definitely worth a look due to its small footprint yet impressive performance.

Genaveve Bradshaw, Nick Miley, and Ryan White