Coway Airmega 400 vs 250: Room Size Is the Deciding Factor

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Same Design, Different Scale

The Coway Airmega 400 and Airmega 250 share the same core design principle: dual-sided intake, bi-directional airflow, three-stage filtration (pre-filter, Green True HEPA, activated carbon). The difference is scale. The 400 is built for larger spaces; the 250 is built for medium rooms.

This is not a case of "which is better" — it is a case of "which is sized for your room."

Specs Compared

| | Airmega 400 | Airmega 250 |

|---|---|---|

| CADR (smoke) | 350 | 240 |

| Advertised coverage | 1,560 sq ft | 930 sq ft |

| Real coverage (4 ACH) | ~680 sq ft | ~465 sq ft |

| Dimensions | 14.8 × 14.8 × 22.8 in | 13.9 × 8.2 × 20.2 in |

| Weight | 24.7 lbs | 13.2 lbs |

| Noise (highest speed) | 52.8 dB | 51.3 dB |

| Noise (sleep mode) | 22 dB | 22 dB |

| Price | $350-450 | $220-280 |

| Filter cost (annual) | $70-90 | $50-70 |

What the Coverage Numbers Mean in Practice

The advertised coverage figures (1,560 sq ft for the 400, 930 sq ft for the 250) assume 2 air changes per hour — the standard used for regulatory claims. For meaningful allergen or particle reduction, you want 4-5 ACH.

Divide the advertised coverage by 2 to get a realistic 4 ACH coverage estimate: the 400 effectively handles around 680 sq ft and the 250 handles around 465 sq ft at that rate.

This means:

A 300 sq ft bedroom: either model works; the 250 is adequate at 4 ACH, the 400 gives extra headroom
A 500 sq ft living room: the 250 struggles at 4 ACH; the 400 is the right fit
A 700+ sq ft open floor plan: the 400 is undersized at 4 ACH; consider two units

Smart Features: Both Have Them

Both models include auto mode (adjusts fan speed based on built-in air quality sensor), sleep mode (runs quiet at lowest speed), air quality indicator light ring, and a timer. Both connect to the Coway app for remote control, scheduling, and air quality history.

The 400 has an additional "Eco mode" that turns the fan off completely when air quality stays at Good levels for an extended period — reducing energy use but also reducing air changes. For people with allergies, leaving auto mode without Eco is usually the better choice.

Which to Buy

**Choose the Airmega 250** if your room is under 400 sq ft and you want a smaller footprint. The oblong shape (vs the 400's square design) also makes it easier to place against a wall.

**Choose the Airmega 400** if your room is 400-700 sq ft, or if you want the unit to run on a lower, quieter speed to achieve the same ACH (a larger unit at low speed is quieter than a smaller unit at high speed in the same room).

The $100-150 price difference is worth it for the 400 if you have a living room or kitchen over 400 sq ft. For a dedicated bedroom, the 250 is typically sufficient.

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