The Ultimate Buying Guide: Coway Airmega 400S Air Purifier

After an enormous amount of research, decided on this unit for a large open space ~1000’sq. Looks good, and feels of high build quality.

This purifier moves a lot of air on its Max setting, and you can feel the air movement from several feet away. It blows upward, so not a breeze like from a fan, but a gentle air movement circles the room. It’s also very quiet. In low you cannot hear anything, even standing beside the purifier. Medium adds a little white noise to the room. High is noticeable, but not a nuisance.

Pros: “Smart” air purifier boasting a high CADR, attractive unit, solid build quality, decent price, and dual 12-month HEPA filters make this a smart investment. Dual handles make this easily manoeuvrable.

Cons: Filter availability.

The App: The app is decent, not great. It’s basically a remote control (on/off, fan speed) with a custom schedule builder if you don’t want the Auto mode enabled. Offers filter life indicators/notifications as well as indicators/notifications when to wash the pre-filter filters. Air Quality Index (AQI) is not available in North America.

If the 400S (“S” = Smart) is a few bucks more than the 400 (standard) then go for it… but consider how much more you are willing to spend for the ability to control fan speed and receive notifications on your phone.

Filters are not easy to find, perhaps due to the popularity of HEPA in the age of COVID, …but like face masks, hand sanitizer, and toilet paper… I’d expect that to normalize soon. All said, we’re happy. Would not hesitate to purchase again.

First off this filter is very large and the filters within it are huge in comparison to other competitors (Detailing Honeywell AirGenius 4 / 5 , Honeywell HEPA HPA300, and Molekule below). Check out the overall measurements of the unit before ordering it – 15″ by 15″ by 23″ tall.

First off, this purifier is BIG, and has TWO LARGE HEPA / Charcoal filters on each side. The HEPA will remove 99%+ of air contaminates and the Charcoal will scrub any smell. Do you have dogs or live in an area with bad air quality? Get this! The only downside is that the filters need to be replaced once a year and typically around $120 for the full set, you dispose the old ones. But when it comes to health . . . just do it. I had “Cleanable” filters in the past such as the Honeywell AirGenius 4 & 5 , let me say when you have to do it 4 times a year, I rather just pay $120 for the set. It typically takes 45 minutes each time to clean the AirGenius and about 4-5 hours to dry.

The Coway Airmega 400s purifier also has a fine mesh pre-filter on each side of the unit (before the main HEPA / Charcoal). It is VERY fine, and is meant to capture hair and other items (heavy dust). These do not need to be replaced, instead they are cleaned manually, some say just clean them with water using a garden hose . I would be very careful using a hose since the fine mesh could tear. Instead I would recommend wiping them down by hand with a paper towel to remove the fine debris then fill up a bath tub and swirl them around a few times, then let them pat them dry with a towel and let them air dry.

I first had the Honeywell AirGenius 4’s and 5’s for a few years but decided to move away from them because of health concerns related to the ozone producing electrostatic filter. I’ve heard of respiratory problems and other issues arising from the ozone they produce, even the EPA recently released some documentation on electrostatic filters, so I decided to move to a Honeywell HEPA equivalent.

Next I moved to the Honeywell True Clean HEPA HPA300 ($250 each), this unit is also very big with 3 HEPA filters (much smaller filters than the Conway but it has 3 of them instead of 2, and a large replaceable charcoal filter in front of the HEPAs. Although a great unit, I wanted more coverage instead of buying more of these. Consumer reports rates this their top 3 filters on the market, if you have a smaller apartment / condo and want to save some money, this one is great and the replacement filters are half the price (but a little less than 60% of the coverage at around 465 square feet – i’ll explain soon why the Coway Airmega 400s should only only be rated at 780 square feet).

Lastly I moved the Molekule setup ($800 each) , although a very attractive unit the pre-filter is TINY and got clogged all the time. The pre-filters on this thing vs. the Molekule are maybe 6 times the surface area and there is TWO pre-filters in here, so around 12 times the pre-filter surface area. The HEPA filter in the Molekule feels like a toy compared to the giant ones in this unit. The only advantage the Molekule has is that it contains a light killing coating on the filter activated by a UV light within the unit. If Coway added a UV filter post stage they will own this market.

In regards to color unit in all the pictures i’ve seen show it black, this is not true, its a very attractive gray on all side, and black on the top and feet.

The power of this unit is amazing, if you turn it up all the way IT IS LOUD, but at the lowest setting I don’t really notice the unit, other items in my room make more noise. There is a big leap in power output and sound from level 1 to level 2. Technically there is 5 settings, sleep, level 1, level 2, level 3, and smart which will just move the settings around using the smart sensor within the unit.

Does it clean the air? That should be the most important question! The air smelled smelled noticeably cleaner after using this unit for a day and coming home. If I cooked something right away my house didn’t smell of the food, those charcoal filters work great!

How may do you need? The 1560 square feet is not accurate, that is for 2 full air scrubs per hour. Technically the rating is suppose to be 4 full square footage air scrubs an hour per the CADR (Clean Air Delivery Rate standard). Then you need to think about if you sleep with your bedroom closed at night you won’t get filtered air in there, or if you put the filter in your room the rest of the house will not get airflow. So really this should be rated for 765 square feet at 4 full air scrubs per hour, which is still better than anything on the market! Even the big HoneyWell unit is rated for 465 square feet, and the Molekule is rated for ~400 square feet when you normalize it. I’m going to put some recommendations below, but if you can only afford one unit, don’t worry, even 2 full air scrubs an hour is AMAZING, better then most things out there. If you keep it running 24 hours a day your house will be VERY clean.

My 2 cents in an IDEAL situation (if you have the extra money to spend):

In single floor house I would get one for the master bedroom and one for a common area (living room, kitchen, dining room) as far away from the bedroom as possible. This will ensure while you are sleeping you get clean air and so does the rest of the house. If you have a two floor BIG house I would recommend getting 3 units with the 3rd unit being upstairs in a common area or in a kiddo rooms. 3 units should be good for 2300 – 4680 square feet if you take the full 4 full air scrubs into consideration or Conways 2 full air scrubs an hour.

The only downside is the app setup, once working it is great on Apple. On Android it is a mess, I think they ported it over from Apple to Android and didn’t finalize their QA.

I was NOT successful adding this unit to my 5Ghz network. It doesn’t let you select your wifi from a list, instead it grabs the last wifi you were connected to. So first thing, connect your iphone to your 2.4Ghz network. Then start the setup.

One important thing I documented in my pictures is where the buttons are. They aren’t the big round things on the left side needed to start the wifi paring, those are just indicators. You touch the screen printed area that i’m pointing at in the pictures in order to start the wifi pairing (Follow the app instructions).

The unit is turned on by the big power button, but the level is controlled by the touch arc between the power button and the screen printed area of power level.

You will probably get a API request timeout in the app the first time you set it up, just force kill the app (on your iphone X swipe up to pull up the app carousel, then swipe up again to force kill the app, on iphone 4 to 8 double touch your home bar to bring up the app carousel, then swipe up again to force kill the app). On the second reload everything will work great.

Other then those small hangups on setup and getting the app working for the first time, it has been great. I think the app is pretty well laid out and informative.

The app will tell you when to change your filters, what your air quality looks like over the last few hours / days / week, give you the ability to turn on and off the unit by a schedule, adjust the fan levels, order new filters, etc.

If you don’t use the app there is a lit up circle on the front of the unit that will tell you your current air quality and notify you if you need to clean or change your filters (clean pre filters or change once a year your HEPA / Charcoals).

Coway if you want to own this market and steal the market share away from dyson, honeywell, and everyone else on the market, revise your app with better QA and a better UX, it is a little rough. Add a post UV filter. Add another step between fan level 1 and fan level 2. Get this in costco, best buy, or consumer reports.

I highly recommend this unit. The prices now are currently amazing so there is no reason you shouldn’t get this!

The filter itself has provided phenomenal filtration for approx. 600 sq ft space. The circular LED particle display is very sensitive to report dust or humidity passing inside the sensor with different colors. The filters themselves are obviously made with the highest quality, and are multi-stage and readily suck up smoke, most smells and dust. The circular indicator goes yellow or red when it detects particles and gradually absorbs the particulates until the indicators returns to the reassuring “blue-green” color.

I bought this to combat smells migrating from a neighbor in the unit below. It does a valiant job. The neighbor is a formidable foe, however. So I don’t fault the unit. The filters are quite expensive. The filter has last months so far, and the LED filter life indicator suggests it is half expended. I have cleaned the fine metal screens, running them under water to rinse off dust rather than letting it go airborne again. The clean-the-metal-screen indicator activates pretty often—about once a week—which is more than I would expect. It is not a big chore, but I didn’t know I would have a job to do to maintain the filter, albeit minor. Air quality has been good, so worth it. The activated charcoal elements do work, however, with the challenging smells from below (cooking? smoking? who knows?) I do use Febreeze spray from time to time to freshen things up and quickly bump things up to a fresher level inside.

I thought the unit would be too big for the space, but with the neighbor issue, it has proved to be right-sized to the task. I usually run it on level 3 while at home, which has an acceptable sound level and also creates a smooth white noise to filter out some of the neighbor’s odd noises as well. But when I leave, I boost it to 4 to catch any violations while I’m gone, so the air is fresh when I come back. The highest setting is quite loud, but if you want clean air “now” it is nice having the extra horsepower when needed. When absent, I’ll use 4 to guarantee things are clean.

Over the winter, wood smoke from outside would settle at ground level with atmospheric inversions pretty often. It was really nice to have “clean room” of air and a reprieve from the smokey outside air. Annual forest fires that come every summer summer will give this filter a workout, too, but I’d expect it to do well.

I would recommend the filter. However, I took one star off for the app. I was very uncomfortable with the language I found on end user license agreement (EULA) which seems to grant broad-brush license to this Chinese company to use your information any way it wants, or give it to anyone it wants. With such a customer-unfriendly EULA, it caused me to wonder what unadvertised “features” this unit might have. Why does it need so much access? But more importantly, I’m not sure what data you must “OK” when installing and using the app on your phone. Is this spyware? Does it slurp up your contacts and other personal info and send it back to the mothership? The EULA created just enough doubt that even though I have the WIFI model, I decided NOT to use the smart app features from my phone and not to install the app, which has been fine. However, I paid extra to have this feature and was a bit disappointed by the level of intrusion the app wanted and Coway’s invasion of privacy.

I leave the filter running 24/7 anyway, so the app really isn’t all that necessary. The circular LED status display gives sufficient feedback to make occasional adjustments when needed, so changing settings isn’t often enough to need a phone app anyway.

Overall, I would recommend the unit, but not the WIFI version. The prices rose immediately after I ordered the WIFI model, such that the higher price for the non-WIFI unit made it the same price as what I paid for the WIFI version—so I just kept it. (The price has gone up 50% since I purchased, so I’d suggest watching for sales. I would not have purchased this at the current price.)

I tried an assortment of different filters prior to buying this one to combat the inside air problems with the neighbor. This is the only one that had enough oomph to truly make a difference. This unit would be great for apartments or condos with shared walls or floors where you may not have full control over neighbor activities.

A miscellaneous comment. The bright circular LED status light can be turned off at night. It also serves as a fairly bright night light if left on in living spaces at night. I suspect the app can control this, too, but I’ve opted to do it manually.

I will have to consider whether I’ll get the genuine Coway filters (yes, there are two large filter panels inside with a massive filter area) which are quite expensive, or one of the seemingly identical no-name filters at half the price. The reviews suggest the knock-offs may work as well. I’d be willing to try them.

I can’t say anything about air quality improvement, because I never had a problem, maybe? I do know that this machine is working on something. It is super quiet while idling on low fan. I don’t even hear it over normal household noise, even when I am sitting 6 feet from it .

I keep it on smart Mode. It ramps up the fan automatically to high when the lights turn pink and red. When my wife sprays Lysol in the house the unit gets pissed off and turns red for a minute. You will hear the fan when it turns up for pink and red light.

When the kids are running around the house kicking up dust the light stays purple until they chill out. We watched a friend’s dog for a week and the light would turn purple more often than normal.

I run a wood pellet stove as my only heat source all winter in new England. When I started running the stove this fall the light turns purple every so often, for a minute.

Finally, it is easy to clean. It looks nice. I like watching the light change colors as normal activities occur in the house. My wife is happy because she told me to buy one. Win win, no disappointment. I purposely avoided the smart model, I’m not that fancy.