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Coway Airmega 400 Review and 400 vs 400S vs 300 vs 300S Comparison

Coway makes some of the most popular air purifiers currently on the market. When recently selecting a model for a comparison, we chose the Coway Airmega 400. Below we’re sharing our Coway Airmega 400 review after testing the air purifier in our studio.

Coway Airmega Review - 400 Model
Coway Airmega air purifier purchased for this review. © Vacuum Wars

After our review, we’ll cover the differences and similarities between the 400, 400S, 300 and 300S Airmega models. For the sake of the review, we’ll be specifically sharing an Airmega 400 review–all our testing was done with that model. 

Coway Airmega Review

About the Airmega 400

The Airmega 400 is designed for large spaces. Coway describes this in a couple of ways. Suggested coverage is 1,560 sq.ft. In rooms of that size the 400 is capable of doing two full air changes per hour. If compared with an air purifier citing one ACH (air change per hour) that number doubles to 3,120 sq.ft.

Coway Airmega 400
Coway Airmega air purifier

Coway also provides their own CADR (clean air delivery rate) numbers of 328 for smoke, 328 for dust and 400 for pollen. In the comparison table below we also included Energy Star’s numbers for reference.

Notable features

There’s much more to talk about where features are concerned. We’ve saved most of the features for the comparison section below. But, a few notable features include:

Our Tests and Other Coway Airmega Models

Performance for the 400 and 400S should be all-but identical as they are the same air purifier offered with a different set of features which are unrelated to our testing. 

Coway Airmega Measuring Noise at Different Fan Settings
Measuring noise level at each fan speed. © Vacuum Wars

The 300-series Airmega models share the same filter technology but are in a smaller package that includes a smaller motor. So, while they do share the same type of filters, our test results don’t apply to those models. The differences we’ll focus on are around features, functionality and why you’d choose one series over the other. 

Air purifier resources
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Particle Reduction Test

The Airmega 400 (as well as the 400S, 300 and 300S) have the same three-stage filtration technology. We’ll go into it a bit more below, but it includes a washable pre-filter, HEPA filter and activated carbon for VOCs and odors. Here’s how it performed.

Coway Airmega 400 Particle Reduction Test
Our Coway Airmega 400 during the particle reduction fog test. © Vacuum Wars

In our filtration tests we evaluate both particle and VOC filtration. In our fog test we see how well an air purifier can clear 12 seconds worth of fog in a ventless room. We set the test up and put the Coway Airmega 400 at its highest fan setting. We measured the 400’s performance at 32 particles per minute, an above average score.

RELATED: See our Airmega 400 vs Nuwave Oxypure review and other recent air purifier reviews!

VOC Reduction Test

Our VOC test is conducted by putting the air purifier into a sealed refrigerator, adding a set amount of incense smoke, then measuring the air purifier’s ability to clear the VOCs in 5 minutes. The Airmega 400 successfully cleared 100% of the VOCs on Max power, another strong showing as not all air purifiers we’ve tested have performed this well.

Coway Airmega Air Purifier VOC Reduction Test
Testing VOC reduction. © Vacuum Wars

Formaldehyde Reduction Test

The Airmega 400 also achieved a near-100% reduction in formaldehyde in our tests, another notable success. Having two sets of filters both with activated carbon undoubtedly tipped the scales in its favor.

Overall, the Airmega 400 performed very well in our tests with better than average or well better than average results.

Coway Airmega 400 - Replacing Filters
The Airmega 300, 300S, 400 and 400S all have two sets of filters. © Vacuum Wars


The Coway Airmega 400 performed great in our tests and has a long list of features (see below). Coway seems to have arrived at a good balance of features, performance and price with the Airmega 400, and we think it’s definitely worth consideration when shopping in this price range.

The Coway Airmega Line

Currently, Coway sells around twenty different Airmega air purifier models. Inside the product line are the 300 series and 400 series and their S-badged counterparts, the 300S and 400S. They all look identical on the outside (beyond the size difference) and that carries through to the inside in many ways, too. 

Coway Airmega 300
Air Purifier

Coway Airmega 300

Coway Airmega 300S
Smart Air Purifier

Coway Airmega 300S

Coway Airmega 400
Air Purifier

Coway Airmega 400

Coway Airmega 400S
Smart Air Purifier

Coway Airmega 400S

When we purchased the Coway Airmega 400 for our comparison there were three additional models we considered before purchase: Airmega 400S vs 400 vs 300S vs 300. Here’s both the similarities and differences between the models.


The Airmega 400, 400S, 300 and 300S have a lot in common.


All four air purifiers have an identical filter set on opposing sides of the air purifier. Coway has branded some of the naming of the filters, but each set essentially adds up to the three levels of filtration found in most higher-end air purifiers:

  • Pre-filter – Traps larger particles, extending the life of the other filters.
  • HEPA filter – Captures 99.97% of ultrafine particles
  • Activated carbon filter – Removes odor-harming gasses like VOCs and neutralizes odors including cigarette odor, pet smells, sulfur dioxide, acetaldehyde and nitrogen dioxide
Activated Carbon Mesh
The activated carbon mesh on one side of the unit’s HEPA filter. © Vacuum Wars

Coway also notes their Green True HEPA filter is capable of capturing “99.97% of ultra fine particles like viruses, bacteria, fungi and pollen” and that the filter has a microbial treatment to “deactivate the spread of contaminants.” 

Coway Airmega HEPA and Activated Carbon Filter
Combination HEPA and Activated Carbon Filter (HEPA side showing). © Vacuum Wars

The Airmega 300, 400, 300S and 400S all have the same filter technology and configuration with the difference being that the 400S and 400 have a larger filter than the 300S and 300.

Filter life is quite good with Coway suggesting replacement annually.


All four air purifiers are packed with features. The standouts include:

  • PM2.5 particle sensor – An onboard sensor provides real-time air quality monitoring.
  • Air quality indicator – An air quality indicator on the front of each air purifier displays one of four colors describing the air quality (see below).
  • Auto mode – A PM2.5 particle sensor automatically adjusts the fan on the 400, 400S, 300 and 300S based on changing indoor air quality.
  • Eco mode – Eco mode is like Auto mode but when each Airmega air purifier detects the air is cleaned, it completely turns the fan off until it detects pollution.
  • Sleep mode – In sleep mode the fan rotates very slowly decreasing the noise the air purifier generates.
  • Filter Status Indicators – Illuminates when the filters need to be washed or need to be replaced.
  • Timer – Set the air purifier to run for 1, 4 or 8 hours before turning itself off. 

Each of the air purifiers also includes a 5 year warranty.

Coway Airmega 400S vs 400 vs 300S vs 300 Comparison Chart

Airmega 300Airmega 300SAirmega 400Airmega 400S
Pre FilterYesYesYesYes
HEPA FilterYesYesYesYes
Carbon FilterYesYesYesYes
Fan Speeds4444
Particle SensorPM2.5PM2.5PM2.5PM2.5
1 ACH2,512 sqft2,512 sqft3,120 sqft3,120 sqft
2 ACH1,256 sqft1,256 sqft1,560 sqft1,560 sqft
4 ACH628 sqft628 sqft780 sqft780 sqft
Auto ModeYesYesYesYes
Eco ModeYesYesYesYes
Sleep ModeManualAutomaticManualAutomatic
CADR (Dust)306306328328
CADR (Smoke)285285328328
CADR (Pollen)339339400400
Dimensions13.6 x 21.2 x 13.613.6 x 21.2 x 13.614.8 x 22.8 x 14.8 in14.8 x 22.8 x 14.8 in
Warranty5 yr5 yr5 yr5 yr
Where to BuyAmazonAmazonAmazonAmazon
Specification from the Coway website and product manuals.

Differences – Airmega 400 vs 400S vs 300 vs 300S

The most helpful comparison is to look at the S versions versus the non-S versions, so the 400 vs 400S and 300 vs 300S and then the difference between the 300 series versus the 400 series.

Coway Airmega 300 vs 400 and 300S vs 400S

The difference between the Coway Airmega 300 and 400 is that the Core 400 is designed to purify the air in a larger area than the 300. Specifically, Coway recommends the Airmega 300 for 1,256 sqft of coverage and the Airmega 400 for 1,560 sqft.

It is also physically larger and has a bigger motor to handle processing the higher volume of air. As far as features and functionality, the 300 and 400 have the same features set and perform the same functions.

The same holds true when comparing the 300S and 400S. The difference between the units is the same as the non-S models.

Coway Airmega 300 vs 300S and 400 vs 400s

The difference between the Coway Airmega 300 and 300S and 400 and 400S models is that the 300S and 400s are smart air purifiers with additional features. 

The Airmega 300S and 400S have the following features which the 300 and 400 models lack:

  • Voice Control
  • Amazon Alexa Compatibility
  • Google Assistant Compatibility
  • Scheduling
  • Control and Monitoring using the Coway App
  • Sleep Mode is Automatic as opposed to Manual
Coway Airmega 300
Air Purifier

Coway Airmega 300

Coway Airmega 300S
Smart Air Purifier

Coway Airmega 300S

Coway Airmega 400
Air Purifier

Coway Airmega 400

Coway Airmega 400S
Smart Air Purifier

Coway Airmega 400S

Which to choose

The Coway Airmega 300, 300S, 400 and 400S all have a strong set of shared features. The first thing to consider when choosing which to buy is the size of the room or area you will be using the air purifier in.

As we noted, the 400 and 400S are for larger areas than the 300 and 300S. In the comparison table above we provided Coway’s figures for both a single and two air changes per hour.

Between the 300 and 300S and 400 and 400S the decision is also straightforward. If you want the app-enabled smart features that the 300S and 400S models have, then choose one of those. If you don’t have a need for them, you can save a little money by choosing the 300 or 400.


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