Current prices were checked on Amazon on October 16, 2026. Only the AirDoctor AD3500 could be found on Amazon. Size, noise and filter-cost figures come from the older page and the makers and were not retested. The older page’s Airmega 400S yearly filter cost was corrected.
AirDoctor and Coway are two of the best-known premium purifier brands. Here is how they compare in small, medium and large sizes, and what the filters really cost.
Table of Contents
AirDoctor vs Coway at a Glance
The older page set three AirDoctor models against three Coway models by size. AirDoctor sells through the AirDoctor store, and only the AD3500 could be found on Amazon, at $559.00. All three Coway units are on Amazon: the Airmega 150C at $189.99, the 250S at $449.00 and the 400S at $612.00. AirDoctor has seven models and Coway about fifteen, per the older page.
Small Rooms: AirDoctor 2000i vs Coway Airmega 150
The AirDoctor 2000i is 14 by 6.6 by 18.7 inches and weighs 10 pounds. The Airmega 150 is 13.4 by 6.5 by 18.5 inches and weighs 12 pounds, in three colors. The 2000i has four fan speeds, an auto mode, a dim mode, an ion setting and Wi-Fi. The Airmega 150 has three speeds and an auto mode. Both have a CADR near 152 to 153 CFM. At that airflow, a 244 square foot room gets an air change in about 12 minutes. The Airmega 150 runs at 20 to 48 dB and 35 watts, against 38 to 59 dB and 11 to 110 watts for the 2000i. See what CADR means.
Medium Rooms: AirDoctor 3500i vs Coway Airmega 250S
The AD3500i is 15.7 by 8.3 by 23 inches and 18 pounds. The Airmega 250S is 18.5 by 8.3 by 19.7 inches and 20.5 pounds. The AirDoctor has a CADR of 326 CFM, enough for 505 square feet at five air changes an hour. The 250S has 249 CFM, enough for 372 square feet. The Coway runs at 22 to 54 dB and up to 64 watts. The AirDoctor runs at 39 to 59 dB and 11 to 110 watts.
Large Rooms: AirDoctor 5500i vs Coway Airmega 400S
The AirDoctor 5500i is 16 by 16 by 29.7 inches and 33 pounds, with wheels. The Airmega 400S is 14.8 by 14.8 by 22.8 inches and 24.7 pounds. The AirDoctor has a CADR of 560 CFM, enough for 868 square feet at five air changes an hour. The 400S has 328 CFM. The Coway claim of 624 square feet works out to an air change in about 15 minutes, a little under five an hour. Noise is 30 to 50 dB for the AirDoctor and 22 to 52 dB for the Coway.
Looking ahead, the filter bill is where this match-up gets decided. Coway sells one combined filter, the Max2, and AirDoctor sells a carbon filter and an UltraHEPA filter apart. The older page did the Airmega 400S math wrong, and the fixed numbers change the picture. The catch is that the cheaper unit up front is not always the cheaper unit over three years.
4 Air Purifiers to Compare
Prices and ratings were checked on Amazon on October 16, 2026.
Price on Amazon: $189.99 | 4.4 stars from 553 ratings (checked October 16, 2026)
The Coway Airmega 150C is listed for up to 1,035 square feet with a true HEPA filter, a carbon filter, a washable filter, an air quality monitor and a 3-year warranty. It has a 4.4 rating from 553 ratings.
Price on Amazon: $449.00 | 4.2 stars from 255 ratings (checked October 16, 2026)
The Coway Airmega 250S is listed for up to 1,860 square feet with app control, a washable pre-filter, a HEPA filter and a 3-year warranty. It has a 4.2 rating from 255 ratings.
Price on Amazon: $612.00 | 4.4 stars from 977 ratings (checked October 16, 2026)
The Coway Airmega 400S is listed for up to 3,120 square feet with a HEPA filter, app control and a 5-year warranty. It has a 4.4 rating from 977 ratings.
Price on Amazon: $559.00 | 4.7 stars from 485 ratings (checked October 16, 2026)
The AirDoctor AD3500 is listed with UltraHEPA filtration and cleaning 630 square feet in 15 minutes. It has a 4.7 rating from 485 ratings.
The risk to watch is the coverage claim. The older page rated the Airmega 400S for 624 square feet at five air changes an hour, and the Amazon listing says up to 3,120 square feet, which is about one change an hour. Expect more listings that lead with the largest number. Use the five-times figure for allergies or smoke, and plan for two filter changes a year on any combined filter.
Filter Cost, Corrected
Filters decide the cost over time. Per the older page, the AirDoctor combo packs cost $135 for the 2000i, $179 for the 3500i and $375 for the 5500i. The Coway Max2 filter costs $50 for the 150 pack, $79 for the 250 and $129 for the 400, and Coway says to change it every 12 months, though carbon wears faster. The older page said the Airmega 400S would cost $464 a year, but that doubled a two-pack price. A 2-pack at $232 covers a full year with two changes, so the corrected cost is about $232 to $258. Use the air purifier filter replacement cost guide. All these prices come from the older page, so check the current price before you buy.
Which Is Better?
AirDoctor wins on airflow and its filter claim in every pair. Coway wins on price, noise, power and availability on Amazon. For a small room, the Airmega 150C is the better value. For a very large room, see our Coway Airmega 400 review. For the mid-size choice, read the Coway Mighty review and air purifiers for large rooms.
FAQ
Which cleans more air, AirDoctor or Coway?
AirDoctor, in every pair. The 5500i has a CADR of 560 CFM against 328 CFM for the Airmega 400S.
How much do Coway filters cost per year?
About $79 a year for the 250S and about $232 to $258 for the 400S, per the older page. Check the current price.
Which is quieter?
Coway, on low speed in all three pairs and at the top speed in the small and medium pairs. The AirDoctor 5500i is slightly quieter on high, at 50 dB against 52 dB.
Where can you buy them?
All three Coway units and the AirDoctor AD3500 are on Amazon. The other AirDoctor models are sold on the AirDoctor store.
Final Word
AirDoctor moves more air and has the stronger filter claim. Coway costs less, runs quieter and is easy to buy on Amazon. Match the size to your room first.
What happens next: expect both brands to push app control and bundle filters by the year. Coway is already selling the Airmega line on Amazon at lower prices than AirDoctor sells on its own site.
Related Guides
Keep going with Coway Mighty review, Coway Airmega 400 review, what CADR means, air purifier filter replacement cost guide and air purifiers for large rooms.
