Coway AIRMEGA 400S Air Purifier Review

AIRMEGA 400s - air purifierI chose this air purifier for my next review due to its ability to service very large rooms (up to 1560 sq. feet, as the manufacturer claims), its “smart” connection to Alexa and numerous sensors. Even though I wasn’t impressed with the design, the variety of smart options quickly caught my attention. I lead a busy lifestyle, just like many of you, so an ability to control the air purifier at a distance appealed to me.

Coway have a reputation for building good quality purifiers. The most famous of which being the sleek ap1512hh, we reveiwed earlier in the year.

The Airmega 400S seems to have a good filter combination, four fan speeds, and a nice control panel. The price is a bit high, though but what you kind of expect for a unit that can service such large areas.

Let’s take a closer look to find out if the unit is truly worth the money the manufacturer is requesting.

Filtration System

Airmega 400s has two washable pre-filters, two trueHEPA filters, and two activated carbon filters.

Washable Pre-Filter: This pre-filter is designed to catch large hair, dust and dander particles floating around your rooms. Its main goal is to allow the HEPA filter to work longer without being clogged by big contaminants. In case you use the air purifier about 8 hours a day, you need to clean this filter once every 2 weeks. You can either vacuum the filter or, in case it’s really dirty, rinse it under tap water.

Max2 Filter Set : TrueHEPA. This set contains Green TrueHEPA filter, which catches 99.97% of all particles 0.3 microns in diameter. This means it keeps your air clean from the mold, dust, pollen, and other contaminants. I’m not sure what Green means in this case, except for the color. I think Coway (the manufacturer) used this word as an advertising trick. But in any case, trueHEPA filter does an excellent job. So “that which you call a rose…”

Activated Carbon filter: The second part of the Max2 set is an activated carbon filter. It deals with 99% of odors, VOCs, and harmful gasses. This is a great filter to have in a large kitchen or a house, where people smoke or vape.

The Max2 filters need to be changed once every 12 months (in case the filter is used about 8 hours a day). The cost of such filter replacement is about $125 (total for two sets) if you buy them from Coway direct. The cost is rather high compared to most air purifiers on the market today. But let’s not forget that this model has 2 filter sets and services a rather large area, for which you may need two standard purifiers.

The air purifier features filter quality indicators so you don’t need to schedule cleaning/replacement. The unit will tell you when you need to start worrying about the filters.


Airmega 400s - filtration system



Airmega 400s - designI’ve reviewed many air purifiers over the years and I can say that the overall design of this model leaves much to be desired. It’s my subjective opinion, but I think the manufacturer could put in some more effort making the air purifier look a little sleeker.

This is a fairly large unit (14.8 x 14.8 x 22.8), which weighs about 25 pounds. It’s not designed to be carried around the house. But since it services a huge area, you probably won’t need to move it anyway. It comes with a handle, though. I think it could use castor wheels as well.

The bright LED ring on the front panel of the purifier lets you know the air quality measured by the sensors. It’s rather large so you can check it out from a distance. Thankfully, you can turn the light off during the night. The rest of the control panel is mostly straightforward.

You can’t install the air purifier near a wall or any other obstacles because the dual suction system collects the air from the sides of the model. You need to make sure the air has free access to the side panels of the unit.

Overall, if you don’t mind the box-like shape of the air purifier, the design is satisfactory. All you have to do is find a place where it doesn’t get in the way, yet doesn’t stand close to any obstacles. It probably won’t be hard in a 1,500 – sq. foot room.


Smart Options and Sensors

Here comes my favorite part. This air purifier has a big variety of smart options, making it one of the top choices for smart home lovers.

Alexa/App compatible

You don’t have to get off the sofa or drive back home if you’ve forgotten to turn your air purifier on or off. Everything you want to do with the purifier, you can handle by using an Android/iOS app or Amazon Alexa. The remote control of the features is priceless for busy people who live in large houses.


Coway created a smart eco mode to save energy. If the air quality stays good for at least 10 minutes, the fan stops working. It restarts only when the air quality becomes poor again. The air quality indicator changes color from green to red to show you the current air parameters.

Sleep Mode

The sleep mode is activated automatically when the room is dark and the air quality is good for 3 minutes. Sleep mode reduces the noise and the power of the air purifier. In case you turn the light on for 5 minutes or longer and/or the air quality in the room falls below moderate, the sleep mode won’t go on automatically. You’d need to handle it manually.

There is one downside regarding the bright lights during the sleep mode. You can turn the air quality indicator off manually (through an app or Alexa) so it doesn’t bother you during the night. However, if you use the timer option (i.e. set the air purifier to start working in four hours.), any time it starts or stops working, the light goes back on.


If you want the air purifier to start working when you are away from home or during the night, you can set up a timer. The delayed start works in 1, 4, or 8 hours, depending on your preferences. You can set up the timer manually or do it with an app.

Air Quality Sensor

This model is equipped with an air quality sensor that helps it regulate the fan speed. If the air quality becomes worse, the fan speed is automatically increased. As soon as the quality improves, the fan goes to the lowest setting or stops if the eco mode kicks in.

You can adjust the sensitivity of the air quality sensor. If you believe that the air purifier increases the fan speed too often, you can decrease the sensor sensitivity from sensitive to normal to less sensitive. This sensor must be cleaned at least once every 2 months in order to work properly.

Noise Levels

You’d expect a large unit like this one to have a very loud fan. However, this is not the case. In fact, the fan has four settings. The fastest one may be called somewhat loud but it doesn’t interfere with your everyday activities. The lowest fan setting is virtually quiet. It’s ideal for the night time. So if you are planning to place this air purifier in your bedroom, you don’t have to worry about getting a good night’s sleep.

The approximate noise levels for Airmega 400s are as follows:

  • Sleep setting – 22 dBA
  • Setting 1 32 dBA
  • Setting 2 45 dBA
  • Setting 3 3 55 dBA

22 dBa is a barely audible sound. It’s comparable to light whisper. Meanwhile, 55 dBA is comparable to a moderately loud conversation or background music. So you get the idea.

Coverage Area

The manufacturer claims that this air purifier can service large areas up to 1,560 square feet, which is rather impressive. Such indication means that one unit can clean a whole apartment or a small house. Let’s look at the CADR ratings:

  • Smoke – 350
  • Dust – 340
  • Pollen – 400

By using our favorite formula (CADR x 1.5), we can see that the recommended coverage area is about 600 – 700 square feet. So the manufacturer’s claim is a bit brave. Conway explains that the air purifier can clean a room of 700 square feet once every 15 minutes and a room of about 1,500 square feet once every 30 minutes.

Anyway, I believe the unit works fine for rooms up to about 1,000 square feet. I think 1,560 sq. ft. is a stretch.

Airmega 400s - coverage area



Conway offers a very attractive 5-year limited warranty. Motor and electronic parts will be replaced if something happens due to manufacturer’s defects.

However, if you are a big fan of warranties, like me, you know you have to read all the terms carefully. Make sure to keep all the receipts/proofs of purchase (if purchased in a store, not online) in a folder so the purchase date is readable. Don’t forget to do all the maintenance on time, otherwise, the warranty may become void.

Even though I didn’t find myself in a situation when I’d need to call Conway’s customer support, I’ve read numerous positive reports about their speed, politeness, and integrity.


  • Services a large area
  • Numerous smart modes
  • Smartphone/Alexa compatible
  • 5-year warranty
  • Two filter sets
  • Quiet operation


  • A slight learning curve (not intuitive)
  • Covers a smaller area than stated by the manufacturer


AIRMEGA 400S Air Purifier Review Conclusion

After doing an extensive review of this air purifier, I can say that it’s worth the money you are paying for it. It’s a powerful unit with numerous smart options and two filter sets. It can take care of large rooms (even though not quite as large as claimed), including basements, garages, and offices. This air purifier comes with an excellent 5-year warrant from a respectable manufacturer.

Also published on Medium.

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