# Coway Airmega 400S - Category: Air Purifiers - Ranking appearance: Also considered (not ranked) - Updated: 2026-08-02 - Canonical HTML route: /products/coway-airmega-400s/ - Ranking context: [Return to the full ranking](/rankings/air-purifiers-wildfire-smoke-allergies-quiet-bedrooms/2026-05.md) Coway Airmega 400S is the connected version of Coway’s dual-filter large-room platform, adding remote control and scheduling for open living spaces while retaining quiet lower-speed operation. ## Verdict Choose the 400S when app control is genuinely useful in a large shared room; choose the ranked 400 when the same core filtration with simpler controls is enough. ## Review The Airmega 400S is a genuine large-room machine, not a broad low-air-change marketing exercise. Coway publishes smoke CADR 328 and 1,560-square-foot guidance at two air changes per hour, plus a 22–52 dBA range. Two washable prefilters and two Max2 filter sets provide substantial particle and carbon surface area, while automatic modes keep lower-speed use civilized. The S suffix mainly buys connectivity: remote air-quality checks, schedules, timers, and app control. Independent testing supports the purifier’s smoke performance and quietness, but owner channels are split on the app and sensor value. The larger practical question is duplication—the ranked Airmega 400 uses essentially the same cleaning platform and already fills the high-output Coway role. ## Why we considered it Airmega 400S adds app control, scheduling, and remote air-quality monitoring to Coway’s proven dual-filter large-room platform without sacrificing its quiet lower speeds. ## Why it missed the ranked list It missed because the non-connected Airmega 400 already represents the same core cleaning platform in the top ten, while the 400S app and sensor record is not strong enough to justify a second near-duplicate slot. The 400S was the first replacement reserve to clear publication review, but it did not enter the original top ten because the Airmega 400 scored higher and already covered the same large-room filtration story. Connected controls create a distinct buyer role for this page, not a reason to pretend it outranked the simpler model. ## What stands out - Smoke CADR 328 and two-sided large-room airflow. - Low-speed quietness with automatic sleep behavior. - Remote monitoring and scheduling on a proven Coway platform. ## Tradeoffs - Near-duplicate cleaning hardware relative to the ranked 400. - A large cabinet and two replacement filter sets. - Mixed app, sensor, and support experiences in owner channels. ## Best for - Connected large living rooms. - Scheduled smoke-day operation. - Buyers who want high airflow at restrained lower-speed noise. ## Not for - Small bedrooms. - App-indifferent shoppers. - Buyers minimizing filter bulk and maintenance. ## Key product facts - **Airmega 400S is rated at smoke CADR 328, with 1,560-square-foot guidance at two air changes per hour.** Coway’s current product page and the ENERGY STAR record corroborate the large-room identity and delivery-rate class. - **The 22–52 dBA operating range, automatic modes, scheduling, and remote monitoring suit large living rooms that also need calm overnight use.** Current Coway documentation lists the sound range, smart modes, app controls, light behavior, and dual-filter maintenance. - **Independent reviews find strong smoke clearing and restrained noise, but question whether the app premium adds enough over the non-connected 400.** Three independent product reviews agree on the large-room performance while treating connected controls and overall value as the main decision point. ## Sources - [Coway Airmega 400S Smart Air Purifier](https://cowaymega.com/products/airmega-400s) — Coway; accessed 2026-08-02. Current US page confirms 400S identity, CADR, room guidance, noise, dual filters, smart modes, app controls, dimensions, and official imagery. - [ENERGY STAR Certified Room Air Cleaner: Coway Airmega 400S](https://www.energystar.gov/productfinder/product/certified-room-air-cleaners/details/4009116) — ENERGY STAR; accessed 2026-08-02. Certification record corroborates fan-and-filter technology, CADR class, room size, efficiency metrics, and listed ozone emissions. - [Filter Maintenance for Airmega 400 and 400S](https://cowaymega.zendesk.com/hc/en-us/articles/6498417702035-Filter-Maintenance-for-Airmega-400-400S-300-300S) — Coway; accessed 2026-08-02. Official support page verifies prefilter cleaning, dual Max2 replacement, reset behavior, and maintenance sequence. - [Coway Airmega 400S Review](https://www.techgearlab.com/reviews/health-fitness/air-purifier/coway-airmega-400s) — TechGearLab; accessed 2026-08-02. Independent exact-model testing covers smoke removal, noise, controls, mobility, and large-room suitability. - [Coway Airmega Review: 300, 400, 300S, and 400S](https://www.consumeranalysis.com/guides/air-purifiers/coway-airmega-review/) — Consumer Analysis; accessed 2026-08-02. Independent family comparison distinguishes the 400S smart features from the 400 and discusses airflow, noise, filters, and value. - [Coway Airmega 400S Review: Real-World Test Results](https://airpurifiershub.com/coway-airmega-400s-review/) — Air Purifiers Hub; accessed 2026-08-02. Recent product-specific home-use review supplies additional context on open-plan operation, sensors, noise, app behavior, and maintenance. ## Buying links and data limits RankReason may provide disclosed marketplace search links, but this page does not store or display live price, availability, rating, review-count, seller, shipping, or offer data. Check the exact model and regional compatibility before buying.