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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
Coway Airmega 400S
Credit: Coway
Top Pick Award
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Price:   $750 List | $649.36 at Amazon
Pros:  Excels in large spaces, extensive control options, great noise to power ratio
Cons:  High operating cost, bulky, app required for some features
Manufacturer:   Coway
By Nick Miley and Genaveve Bradshaw  ⋅  Jun 16, 2022
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80
OVERALL
SCORE


RANKED
#2 of 15
  • Air Cleaning Performance - 40% 9.0
  • Noise - 25% 8.3
  • Ease of Use - 25% 8.5
  • Operating Cost - 10% 2.0

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 quite easy to use (it has both an on-unit and app-enabled user interface) and has a nice exterior design. The unit also has an air sensor that informs the "smart mode" which turns the filter on/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.

Compare to Similar Products

 
Coway Airmega 400S
This Product
Coway Airmega 400S
Awards Top Pick Award Editors' Choice Award Editors' Choice Award Top Pick Award Best Buy Award 
Price $750 List
$649.36 at Amazon
$250 List
$239.90 at Amazon
$230 List
$191.63 at Amazon
$140 List
$139.99 at Amazon
$100 List
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Pros Excels in large spaces, extensive control options, great noise to power ratioExceptional air cleaning performance, very quiet operation, simple user experienceExcellent air cleaning performance, quiet operation, average lifetime costSmall footprint, minimalist design, good performance for its sizeBudget friendly, compact, great performance
Cons High operating cost, bulky, app required for some featuresExpensive operating costExpensive operating costNo timed settings, lacks air quality sensorLoud, doesn't have an automatic air sensor
Bottom Line A high-performance, high-volume machine that has user-friendly interface options and a wider range of controls than other purifiers of its classExcellent, high quality air cleaning performance from a quiet and convenient applianceA top performing model that combines average lifetime costs to create a great valueSmall, powerful, and inexpensive — a great pick for those wishing to filter air in a smaller spaceA budget-friendly and space-efficient model that gets the job done but is a little underpowered for large spaces
Rating Categories Coway Airmega 400S Winix 5500-2 Coway Airmega 1512HH Blueair Blue Pure 411 Levoit Core 300
Air Cleaning Performance (40%)
9.0
8.1
7.9
7.2
7.6
Noise (25%)
8.3
9.3
9.0
8.0
4.0
Ease of Use (25%)
8.5
8.5
7.8
8.0
8.4
Operating Cost (10%)
2.0
5.0
5.0
8.0
7.0
Specs Coway Airmega 400S Winix 5500-2 Coway Airmega 1512HH Blueair Blue Pure 411 Levoit Core 300
Dimensions 14.8" x 14.8" x 22.8" 8.2" × 15" × 23.6" 16.5 x 9.5 x 18.5 16.7" x 8" x 8" 8.7" x 8.7" x 14.2"
Weight 24.7 lbs 15.4 lbs 12.7 lbs 5.3 lbs 7.5 Ibs
CADR 328 CFM 246 CFM 240 CFM 120 CFM 135 CFM
True HEPA (99.97%) Yes Yes Yes No Yes
Estimated Lifetime Cost (5 years) $1,339 $660 $556 $337 $455
Airborn Particulate Reduction After 1 Hour (%) 99.96% 99.99% 99.84% 99.72% 96.33%

Our Analysis and Test Results

Performance Comparison


Coway Airmega 400S air purifier - the coway airmega 400s is a workhorse for large spaces. it has a...
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

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 monitor.


Our analysis of air cleaning performance is simple yet sophisticated and comprehensive. We sealed off a 150-square-foot room and burned incense and paper to bring the Dylos particulate reading to approximately 1500. We then turned on the purifier and recorded the time it took to clean the air. The 400S reduced the particulates from over 1500 to 220 in 30 minutes and down to 2 particles in 60 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).

Coway Airmega 400S air purifier - the robust fan in this unit makes it a go-to for larger spaces.
The robust fan in this unit makes it a go-to for larger spaces.
Credit: Abriah Wofford

Another key component of air cleaning performance assessment is the odor reduction analysis. Burned paper and incense used in this evaluation produce 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 air purifier - the smart mode on the 400s makes use of an air sensor to control the...
The smart mode on the 400S makes use of an air sensor to control the unit's operation.
Credit: Abriah Wofford

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 isn't the quietest model in the class, it's pretty close. 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 assesses the pitch of the motor and fan because, as most readers know, it's not just volume but the type 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 air purifier - 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

While it's not officially part of our assessment, the 400S also has a sleep feature. So, for those folks 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 air quality 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 reasonably 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 well above average. 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).


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. Although, 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 (24.7 lbs) 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 air purifier - the well designed controls on the 400s make it a breeze to use.
The well designed controls on the 400S make it a breeze to use.
Credit: Abriah Wofford

Operating Cost


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 high price — $268 per year. 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 air purifier - this air purifier is among the most expensive to operate, not in...
This air purifier is among the most expensive to operate, not in small part for its high-end HEPA filer.
Credit: Abriah Wofford

Value


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; and also has a good all-around performance. 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 air purifier - the coway airmega 400s has a sleek design and purifies air quickly...
The Coway Airmega 400S has a sleek design and purifies air quickly, even in larger rooms.
Credit: Abriah Wofford

Conclusion


This review of the Coway Airmega 400S covers the unit's air cleaning performance, noise, ease of use, and operating or long-term cost — everything one will want to know before making a purchase. This unit is best suited to larger spaces and performs remarkably well in all of our evaluations except for long-term costs. This unit should be at the top of your list if you want to purify a lot of air.

Nick Miley and Genaveve Bradshaw
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