Comparison

Coway Airmega 300 vs 400 vs 400S

The Airmega 300, 400 and 400S share a tall two-sided layout, sensor-led Auto and color-category feedback, but they solve different room and control needs. The 300 is the smaller local-control choice; the 400 adds room capacity without adding an app; the 400S pairs the larger 400 body and filter arrangement with Wi-Fi and app functions. Start with the air-change rate, then decide whether connected control is worth requiring.

Compare the room at the same rate

Coway lists the Airmega 300 at 1,256 square feet for two air changes per hour and 628 square feet for four. Scaling the two-ACH figure to this site's 4.8-ACH comparison gives about 523 square feet. Coway directly lists the Airmega 400 and 400S at 1,560 square feet for two changes per hour; scaling that figure gives about 650 square feet at 4.8 ACH. These are proportional comparison calculations from Coway's room figures, not independent tests or direct 4.8-ACH labels. The 300's separate 2,512-square-foot one-change headline is a lower repeated-cleaning rate and should not be compared to the 400's 1,560-square-foot two-change area as if their conditions match.

That makes the decision practical: a medium room can fit the 300's comparison range, while a room that requires a conservative large-room tier calls for the 400 or 400S rather than relying on the one-change headline. Both larger models publish separate smoke, dust and pollen CADRs, and the 300 does too; do not treat one pollutant CADR as a generic value. A high ceiling, open connection to other rooms or blocked side intake deserves more margin than a headline estimate.

Local controls or app connection?

The 300 and non-S 400 have physical controls but no app functions. Both offer sensor Auto, manual airflow levels, an Eco mode, Sleep and a color air-quality signal; neither is a numeric PM display on the appliance. The 300 has a one-, four- or eight-hour local timer, and the 400 has the same local timer choices. The 400S is the connected choice: its app adds remote controls and scheduling, but it still should not be mistaken for a numeric PM reading on the unit. The S designation changes the control path, not the underlying room-size tier in this comparison.

Account for size and filter differences

The 300 lists a 13.6-inch body width and depth and weighs 21.4 pounds. Its page and family one-sheet list a 21.2-inch height, but the shared manual says 20.1 inches for the exact 300/AP-1515H model, so use neither height as a hard clearance promise. The 400 and 400S are wider and heavier at 14.8 inches and 24.7 pounds; both sides and the top still need clear airflow. Each model has washable pre-filters and a replaceable pair of Max2 filters, but their replacement sets are listed for different Airmega families. Check the model-specific set rather than assuming the 300's 300/300S pair fits a 400/400S.

In short, choose the Airmega 300 for a medium space and a straightforward local routine; choose the Airmega 400 when the room needs more repeated-cleaning capacity but a phone is unnecessary; choose the 400S when the larger-room fit and connected scheduling are both important. If a must-have numeric on-unit PM value, TVOC reading or specific filter profile is missing from the exact manual and page, none of these three should earn a match by implication. Start with the Airmega 300 review, the Airmega 400 review or the Airmega 400S review for full limits and maintenance details.

Sources: Coway’s Airmega 300 page and linked manual, plus the exact reviewed Coway pages for the Airmega 400 and Airmega 400S.