Coway Airmega 300 vs 400 Comparison

This is a comparison post for the Airmega 300 and 400 air purifiers. I’ve written a few additional notes here, but make sure you check out the full review.

Since discovering I have some seasonal allergies about two years ago, I’ve been looking for a decent air purifier. My place is a large studio, about 850 sq ft, and it’s mostly one room. I was looking for a few things:

  • Capable of purifying coverage for about 700 sq ft
  • Attractive—something I wouldn’t feel like I had to hide
  • A smart or eco mode that prevented it from constantly running
  • Quiet fans

Eventually, I stumbled upon Coway’s Airmega product line. They were highly rated and covered all of the above. More than anything the Airmega is a sleek-looking device—much more than I expected from an air purifier. The only downside is the price of the units.

Coway Airmega 300

Excellent for large rooms and studio apartments

With dual filters and a powerful, but quiet motor, the Airmega 300 is perfect for rooms between 600 and 1200 sq ft. It's strong performance and attractive design make it a standout among a sea of boring air purifiers.

Coway Airmega 400

The best air purifier for very large spaces

Larger and more powerful than the Airmega 300, the Airmega 400 is ideal for spaces 1,200 sq ft or larger. Think very large rooms and open office spaces.

So should you get the Airmega 300 or 400?

After some patience I was able to grab an Airmega 400 on sale for about $450. There were a few things that I wasn’t entirely aware of when I made this purchase. I’ve since returned it for a 300, but here are a few things I would be aware of:

Size. The Airmege 400 is huge. Really huge.

Here is a picture of it next to my IKEA Hemnes nightstand. It is about 2 inches shorter, but amlost the same width and depth. The picture here doesn’t really do it justice. It did not fit in the delivery locker at my apartment complex and I had to go pick it up from the post office.

The truth is that I had not done my homework. The 400 is more powerful with 1,560 sq ft of coverage, but it is also much larger—about an inch in every direction. The 300 is still big, but feels much smaller than the 400.

Filter cost difference.

  • Max2 filters cost about $120/yr for the 400
  • Max2 filters cost about $80/yr for the 300

The Coway Airmega 300 and 400 air purifiers were recently on sale.

Light sensor. The pretty light that helps display the air quality in your home is bright, very bright. In addition to the dust and pollution sensors the 400 has a light sensor that automatically turns the light off at night.

You can always keep the light off. That’s what I’ve done with my 300. But having it auto dim is a nice feature if you’re planning on putting it into your bedroom.

UPDATE: I may need to research this more. Perhaps the 400 does not use the light sensor to turn off the air quality indicator light.

Comparing additional specs

Specifications Airmega 300 Airmega 400
Dimensions WxHxD 13.6 x 21.2 x 13.6in 14.8 x 22.8 x 14.8in
Weight 21.4 lb 24.7 pounds
Purifying Coverage (2 ACH) 1,256 sq ft 1,560 sq ft
Purifying Coverage (4 ACH) 628 sq ft 780 sq ft
Annual filter cost ~$80 ~$120
Noise Level 22~52 dB 22~52 dB
Power usage 57 W 66 W
Sensors Dust / Pollution Dust / Pollution / Light

What about the 300s and 400s models?

There are newer, smart versions called the Airmega 300s and 400s. These versions come with an app that let you remotely see the air quality in your room and control the Airmega. Personally, I don’t see the point. I’ve just set my 300 to smart mode—it comes on when needed. Otherwise I kind of just forget about it.

The newer S models are also generally $100 to $200 more than the base models. It just doesn’t make sense to pay that much more for an air purifier app.

Would a smaller air purifier work?

Both the Airmega 300 and 400 are both attractive and excellent for large spaces. However, if you have several rooms that you’re looking to purify, it would be more effective to purchase a few air purifiers with less coverage.

Coway manufactures the Airmega 200M and Mighty which might work better in this case. They have about 360 sq. ft. of coverage and cost a fraction as much. If you’re trying to purify your living room, bed room and home office it would be more effective to purchase 3 smaller ones than a single large air purifier. It would cost about the same.

If that sounds more like what you need, take a look at our Coway Airmega 200M vs Mighty AP-1512HH Comparison. One of those should work.

First month of the Airmega 300

It is probably too early give long-term notes. Smart mode seems to work well. Usually the fans are off or on low, which isn’t audible. The only times the purifier kicks into medium and high speeds is when I’m cooking something on the stove top. After about 20 minutes it winds down.

The air quality light is very bright at night. I’ve turned mine off.

That’s about all I have to report thus far.

Coway Airmega 300

Excellent for large rooms and studio apartments

With dual filters and a powerful, but quiet motor, the Airmega 300 is perfect for rooms between 600 and 1200 sq ft. It's strong performance and attractive design make it a standout among a sea of boring air purifiers.

Coway Airmega 400

The best air purifier for very large spaces

Larger and more powerful than the Airmega 300, the Airmega 400 is ideal for spaces 1,200 sq ft or larger. Think very large rooms and open office spaces.

Long-term notes

Purchased an Airmega 400 in September 2018 and later exchanged it for the smaller Airmega 300. Since a products flaws can appear after months or years of use, I publish my long-term notes here. That way you can determine how buy-it-for-life the product is.

  • February 5, 2021 A few years in the Airmega 300 is still a powerful and reliable air purifier. We’ve spent significantly more time at home because of COVID. Having a good air purifier has made a significant difference.

  • July 2, 2020 I’ve ordered a replacement Max 2 filter. The indicator light finally came on. I had been a little worried that it was broken. The HEPA filters are supposed to be replaced annually. It appears these lasted almost twice that. I suppose the replacement indicator is based on usage and not on a timer. I’d say this is a big win for consumers and just another reason to trust Coway.

  • August 12, 2019 This Airmega 300 review is published. I am still very pleased with the air purifier. It has just enough “smarts” to be effective.

  • March 29, 2019 My replacement air purifier arrived. Fast shipping, no issues.

  • March 26, 2019 The Airmega 300 has a power issue that I believe was caused my an electrical surge in my place. I had to fill out Coway’s warranty registration form and they sent me a shipping label. I did have to pay $15 for a box to put the old device in.

  • November 4, 2018 I published an article comparing the Airmega 300 and Airmega 400.

  • September 4, 2018 I ordered the Airmega 400 and realized that it was much larger than expected. I exchanged it for the slighyly smaller Airmega 300.

Image from Coway

Hi can either of these air filters be used to clear wildfire smoke from my home? Thanks!

Hi Mari, yes they can!

I should have included a link to the video that made me purchase this air purifier in the first place! Here is a video of the Airmege 400 clearing surrounding smoke in a matter of seconds.

My Airmega tends to go on high mode every time I cook a steak or try and season my cast iron skillet. That’s mostly from the smoke those activities put off. It basically returns my place to normal after about 10-20 minutes on high.

The Airmega will work, but I wouldn’t nessesarily recommend it unless prices isn’t an issue or the space is more than about 800 sq ft. There’s also the Coway Mighty, which is manufactured by the same company, but is about half the price.

To be fair any HEPA air filter should help with air quality due to wildfires. According to Wikipedia, to qualify as a HEPA filter it must remove (from the air that passes through) 99.97% of particles that have a size greater-than-or-equal-to 0.3µm—basically very small particles.

Hope that helps!

1 Like

@Mari_Castillo it’s also probably worth mentioning that while this will mostly work for smoke, it does not have a chemical Volatile Organic Compound (VOC) filter. VOC filters are usually charcoal and filter our gases.

If you want an air purifier that has a HEPA filter in addition to a VOC filter take a look at the Wirecutter-recommended Austin Air HM400.

Austin Air HealthMate

Exellent for particulate and odor removal

A combination of HEPA and activated-carbon filters, the Austin Air HealthMate can remove most odors, VOCs and particulates. It's a comprehensive air purifier, but comes with a higher price.

It’s a bit pricier than event the Airmega, but you’ll have even more filtration.

If you want to spend even more there’s also Molekule, which uses a new technology called Photo Electrochemical Oxidation (PECO). I don’t know that much more about it though.

Well, I’m not sure a VOC filter is needed just for smoke. Any HEPA filter should be fine for removing smoke—that’s why it has been around since the 1950s.

I’ve heard of Molekule a few times since these California wildfires started, but I’m a bit of a skeptic. I just did some research to see what other opinions I could come up with.


This Wirecutter review where they compared air purifiers, but Molekule didn’t a review that wasn’t suprvised.

We requested a model because we were interested in testing its effectiveness on micron-scale particulates and VOC reduction, but Molekule requested that we agree to conditions around the testing—asking that a Molekule engineer or a consulting researcher they’d worked with in the past monitor and advise on our work if we conducted testing on our own.

Hacker News

This comment thread on Hacker News. Particularly the comment by chaostheory.

I had one. It has multiple issues:

  1. CADR is really low to the point where the unit is near useless due to #2

  2. In addition to a low CADR, it has the highest noise. It looks and sounds like a jet engine when you have this thing on high, which is needed due to the low CADR. This is the loudest air purifier that I’ve ever owned

  3. If you get a defective main filter, the unit will emit an unpleasant metallic smell. I haven’t tested the particles yet but I doubt the air is clean.

  4. Unlike other smart air cleaners in the same price range, it’s app and smart features don’t work. You can’t even create a schedule for it

It’s a very flawed device


And there are a few concerning reddit threads—like this one titled What has your experience been with Molekule?

From sAfuRos:

I had a lot of back and forth’s with Molekule CS as an original Molekule pre-backer over a year ago because the filters reek and continue to do so.

Molekule says this is due to “contaminants that may enter the filter during the packaging and transit process” but that sounds like BS to me. I had no less than 5 filters sent to me total (for free, so props to molekule CS for that) and they all had the horrible smell. The smell goes away over time but never fully leaves, such that in a small room the smell will permeate the entire room even months after the same filter has been running 24/7.

After my own research, I believe this is due to the fact that it’s very difficult to bond TiO2 molekules (which is what Molekule is using on the nanofilter) as a coating; you’ll almost certainly get offgassing for the entire life of the filter, as small nano-particles essentially ‘fall-off’. I believe this lines up very strongly with the evidence that others have posted about VO2 levels not decreasing or even increasing; the decrease in other Vo2 compounds is offset by the Molekule’s own offgassing.

From specikk:

Now, on to the Molekule. The first thing that struck me as odd was that the Molekule contains no sensor to monitor air quality-- at least not ones that are exposed to the app or used by the device itself. Perhaps they are in the hardware and will be enabled by a software update? It seems like quite an oversight to not include a basic air quality sensor for a device at this price point.

Molekule is a fairly new company and hardware is hard. However, I can’t recommend spending $800 on this thing. That’s hardly an affordable air purifier. And the reviews and comments so far seem pretty critical.

I hope they can figure it out, because it seems promising.

@Sam In the article, you mentioned you thought the 400 had a larger fan than the 300. Do the units indeed share the same fan, or is the larger fan size in the 400 not material enough to make a difference?

@raneses I apologize. I think the way I worded a couple sentences was a little confusing. I’ll update that.

To answer your question the 400 is both larger and has a more powerful fan than the 300. The metric you want to look at for air purifiers is Air Changes Per Hour (ACH).

  • Airmega 300 in a 1,256 sq ft room will change the air twice in an hour
  • Airmega 400 in a 1,560 sq ft room will change the air twice in an hour

Unless you have a really large room, I’m not sure that you’ll notice a huge difference between the 300 and 400 in day-to-day performance. I keep mine on smart mode and the only time the fan spins up to high is when I’m searing a steak.

Appreciate the comment!

Has anyone looked at the Airmega 200? How does it compare to the 300 and Mighty? I’d love a quick review, if you have.

Considering this is one of the most popular posts on Product Dork, I thought I’d post an update—my Airmega had an LED or power problem. For what it’s worth this was probably caused by a power surge at my place, not a faulty product.

In either case customer service was great and Coway sent me a replacement without hassle.

Did something odd happen to the formatting here? All these responses now have the same date associated with them?

Yeah, this is my bad. I was attempting to change the update to the day that the new Airmega arrived. Unfortunately, it reset the entire topic and all the comments to the same day.

I was able to restore the original post date. Unfortunately it looks like I can’t revert the comments though. That’s why it looks like all of them appear on the same day now.