Coway Airmega 400S Review In 2023: Smart enabled air purifier!

Coway Airmega 400S is the top end in the series so naturally it has best-in-class coverage for all room size. With 2 air charges every 30 minutes, expect a wide 1560 sq. ft. purifying coverage. Coverage drop to half at around 780 sq. ft. coverage with 4 air charges every 15 minutes. For normal non-allergic situation, the 2 charges purifying coverage is sufficient for most. Smart mode is the default mode that will manage autonomous purifying. In Sleep mode, speed will automatically set to low for noise and power reduction. You can also manually select one of the 3 speed to disable Smart mode.
online price (US)**
±749.00 $$$$$$$/ 7

(annual filter cost ±130)

** MRSP (Manufacturer's Suggested Retail Price)/ RSP (Retail selling price) is accurate at the time of posting.
^ Annual filter cost is calculated based on filter price and 12 hours of usage. Pricing could vary depending on air quality, usage frequency, and speed.
` The indicated online price guides as follows: $ = under $50, $$ = $50-100, $$$ = $101-200, $$$$ = 201-300, $$$$$ = $301-400, $$$$$$ = 401-500, $$$$$$$ = over $500.

Coway Airmega 400S Specification

ProductCoway Airmega 400S
14.8 x 22.8 x 14.8 in
(37.6 x 57.9 x 37.6 cm)
Weight24.7 lb (11.2 kg)
Coverage (up to)1,560 sq. ft. (145 m2)
Airflow speed
Dust free (CADR)350 cfm (595 m3/h)
Pollen free (CADR)350 cfm (595 m3/h)
Smoke free (CADR)350 cfm (595 m3/h)
Humidifying(H) speed
- Lifespan
- Replacement cost ($)
Pre-filter (2 pack)
+- 25
HEPA filter
- Lifespan
- Replacement cost ($)
Max2 (Green True HEPA filter)
1 year
Carbon filter
- Lifespan
- Replacement cost ($)
Max2 (Activated carbon filter)
1 year
Ionizer/ Technologies
UV-light/ PCO
Other filter
All-in-one filter
- Lifespan
- Replacement cost ($)
Max2 Filter
1 year
+- 129.99
Optional/ Addon
Noise level22 - 52 dB
Power usage level6 - 66 W
Timer/ Scheduler1, 2, 4, 8 hours (App), Scheduler
SensorsPollution sensor, Light sensor
Auto mode
Air qualityAQ indicator
Filter change indicator
More color options
Wi-Fi/ BTBluetooth
Remote control
Child lock
Warranty5 years
Email/ Phone support

Key Features

  • Wi-Fi connectivity for AIRMEGA app integration
  • Works with Amazon Alexa
  • 4-stage filtration
  • Permanent Pre-filter
  • MAX2 filter (99.999% True HEPA filter + 99% Activated Carbon filter)
  • 3 fanspeed (Low, Medium, High)
  • Dual air suction via side air inlet
  • Dedicated Pre-filter and HEPA filter indicator (Change, Wash)
  • Smart mode - Auto, ECO and Sleep mode
  • Real-time air quality monitor (Good, Moderate, Unhealthy, Very Unhealthy)
  • Adjustable pollution sensor's sensitivity (sensitive, normal, less sensitive)
  • Scheduler/ Timer via IoCare app (1, 2, 4, 8 hours)
  • 5 years warranty

Design and Usability

Simplicity meets modern architecture. Coway Airmega 400S manage to perfect the art of design with its seamless dual side air inlet. The 14.8 x 22.8 x 14.8 in size and 24.7 lb weight is considerably compact for its category if you discounted the four fixed legs. Build quality is top-notch that does not seem to be any signs of ozone off-gassing or air by-pass. Upfront, there is a LED ring AQ indicator with real-time (every minute) air pollution update. Up to four different colors will be shown on the air quality status. Starting from Good (Blue and green), Moderate (Green and yellow), Unhealthy (Yellow and pink) to Very Unhealthy (Pink and red). Finally, to lift or transport the air purifier around, simply hold on to both sides of the handles.

Coway Airmega 400S control

Controls are located at the top black panel that separates into two sections. On the left side, you will find a Wi-Fi button, Light button, Pre Wash button, and Max2 change button. Touching the Wi-Fi button connect the air purifier to a Wi-Fi network. The Wi-Fi LED indicator will start blinking when the pairing is in progress. Once a stable connection is established, the LED indicator will stay constant. The light button will turn on or off the air quality indicator light. Pre Wash button will shows the pre-filter cleaning cycle at 5 levels: 100%, 80%, 60%, 49%, 20%, and 0%. Once the button is lit, you will need to clean the pre-filter. To reset the Pre Wash filter Lifetime notifications, touch and hold the button for 2-3 seconds. The above steps apply to Max2 Change button as well. Instead of cleaning the filter, you will need to replace the Max2 filter. Light sensor function by detecting the intensity of ambient light. When the air purifier is in Smart mode and surrounding is in pitch black for 3 minutes, Sleep mode will activate.

Moving to the right side, you have the big main Power button that is self-explanatory. Touch the button once to turn on the air purifier, touch and hold the same button again for 2-3 seconds to turn it off. To manage the fan speed or purifying mode, either touch or swipe your finger upward or downward on the curve bar. One more secret function that most people didn’t know unless they read the manual (how many of you does that). you can adjust the sensor’s sensitivity by holding on the Light button +Smart bar. Continue by selecting one of the fan speed (speed 1 = sensitive, speed 2 = normal, speed 3 = less sensitive). Overall, all buttons are responsive, clearly labeled with dedicated indicator light.

Like 300S, the Wi-Fi enabled feature that allows you to control the air purifier at any place via IoCare app. Pairing is easy for both Apple and most Android phones so long you have strong Wi-Fi connectivity. We did encounter some issues with some lower end model (Huawei to be exact) that requires few retries. Upon successful connection, you can access features like timer, speed, Smart Mode, and scheduler. Highlights would be on the scheduler that allows you to program weekly activities. You can also access indoor/ outdoor air quality report and Real-time Air Monitoring.

Airmega 400S also works with Amazon Alexa where you could control specific functions. The standard list of voice command includes on/ off, switching mode, fan speed, timer, check filter life, and air quality.

Briefly go through other key specification again. A standard 4-stage filtration, 3 fan speed with Smart mode (Auto/ Sleep/ Eco). Wi-Fi enabled for Airmega’s IoCare app and Amazon Alexa support. Pre-filter/ MAX2 life-time indicator (actual filter real-time usage lifespan). Lastly, air quality indicator, 30 days money back guarantee and 5 years warranty.

Airflow, Coverage, And CADR

Running at a maximum of 1560 sq. ft. with 2 air changes per hour or 780 sq. ft. with 4 air changes or every 15 minutes, the air purifier produces plentiful airflow output. Adding an adjustable pollution sensor, the default Smart mode is there for autonomous purifying. Sleep mode will reduce noise and speed intended for night use. Speaking of night use, 400 can be used in bedrooms or even living halls as it has the capacity for large room sizes.

BrandPurifying CoverageFan Speed
Alen BreatheSmart 45i800 sq. ft.4
Coway Airmega 300S1,256 sq. ft.3
Rabbit Air A3 SPA-1000N1,070 sq. ft.5
Winix AM90230 sq. ft.4
Blueair Classic 405430 sq. ft.3
Blueair Classic 205280 sq. ft.3
CADR is also equally impressive as the purifying coverage. Overall dust, pollen, and smoke have an outstanding 350 cfm figures. Significantly higher than most air purifiers CADR output within its segment. Based on the figures itself, 400S would have no problem handling heap of dust and allergens. Same goes with indoor smoke and odor pollutants.

Recommended Read

Filters And Performance

Airmega 400S uses the same 4-stage filtration setup that is proven against the test of time. Essentially a dual pre-filter plus Max2 filter bundled (True HEPA and Activated Carbon). Each pre-filter would cover both sides of air inlet for incoming airborne contaminants. With large particles out of the way, Green True HEPA filter would focus on trapping 99.999% of microbes allergens. Anything that is 0.01 microns or bigger with not be able to bypass the HEPA filter excluding gas particles. That job belongs to Activated Carbon filter that will absorb nearby smoke and odors. There is no optional Ionizer included in the filtration list; Not a big miss for some.

Noise And Energy Usage

22 - 52 dB noise level is the same as 400 model. Reasonable but not overly silent at low speed and low to normal conversion noise level at max speed. Usable in bedroom if you crank it in Sleep mode. The 6 - 66 watts power consumption is in an identical pattern with noise. Minimal consumption rate at low speed and high consumption rate at medium/ high speed. To further enhance the eco-friendliness, there is ECO mode by will activate automatically. The air cleaner would shut down the fan when the room air quality is good for at least 10 minutes. Auto mode would also prevent any energy wastage where it would only run at a higher speed when requires.
Noise TypeDecibels
Coway Airmega 400S22 - 52 dB
Breathing10 dB
Rustling leaves20 dB
Whispering/ Quiet library30 dB
Light rainfall40-50 dB
Conversation50-60 dB
Vacuum cleaner/ Hair dryer/ Washing machine65-80 dB
City traffic80-90 dB

Pricing And Maintainence Cost

Coway Airmega 400S air purifier is the highest in the brand hierarchy hence it is the costliest. We do think it's worth every penny you paid but some features are not critical to purification. If that's the case, maybe it's time to consider the smaller 300S or other equivalent models. Annual filter replacement cost is more reasonably priced with plenty of availability. Both 400 and 400S uses the same Max2 filter set.
Like Apple, some air purifiers that offer a fixed price across all retailers. Airmega is not one of them. You can get 400S at around 100-200 dollars lower than its RSP price depending on the condition of the unit. We recommend Amazon as it has the highest discount percentage. There is also 30 days no question asked return policy, and free shipping (choice). Coway official channel is not a bad place either with promotional price, free shipping (U.S. only), and easy payment. Certain physical stores like Walmart, Kohls or Bed, Bath and Beyond might carry 400S. Try your luck.

Final Thoughts On Coway Airmega 400S

Overall, we are happy with Airmega 400S practicality and airflow delivery. Make no mistake though, this is a premium model that explains the low numbers (+- 179) of Amazon reviewers. Out of the bunch, 65% of the users gave it a 4-5 stars agree on the HEPA filtration efficiency. They also like how easy the air purifier works with air quality monitor and Smart mode. A few also compliment on IoCare app advanced scheduling feature. As for the negatives 1-2 stars, a high 26% of users dislike the following things. First, Smart mode aka Auto/ Sleep/ Eco that does not react quick enough to the surroundings. Second, IoCare app is virtually unusable since switched to Coway platform. Third, the air purifier is merely ineffective against allergens, smoke or odors. Clearly the pros outweigh the cons and the complaints are fixable. We have confidence the app issue will be resolved in the coming months.


  • 4-stage filtration with the widest purifying coverage in its group.
  • Dual pre-filter covers and protects the HEPA filter from large particles.
  • Outstanding allergens and smoke filtration via MAX2 filter (Full-size HEPA + Carbon).
  • Auto mode accurately adjusts the fan speed based on room air quality.
  • Light/ sleep mode automatically tones down the noise and speed when the room is dark.
  • Separate Pre-filter and MAX2 lifespan indicators based on real-time usage.
  • Timer + advanced scheduler for 7 days customizable via the IoCare app.
  • Legible and accurate real-time air quality monitor.
  • Standard 5 years manufacturer warranty.


  • All Airmega air purifiers are expensive, yet this is the most expensive version of its series. Considered the filter cost too.
  • Slight learning curve on Wi-Fi connectivity, especially for a first-time user.
  • No Ionizer as an option.
  • Timer is only accessible via the Airmega app.

Verdicts And Ratings

Build Quality



Particle Filtration

Smoke Filtration


Filter Cost



Coway Airmega 400S Air Purifier Review

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.

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