Coway Airmega 400 vs Blueair Blue Pure 211i Max 2026

CADR: 328/400 vs 410 — The Efficiency Paradox

The Blueair 211i Max has CADR 410 smoke, 410 dust, 410 pollen. The Coway Airmega 400 has CADR 328 smoke, 328 dust, 400 pollen. Both are AHAM-verified. On smoke and dust CADR the Blueair leads by a meaningful margin — 25% higher on smoke and dust. On pollen CADR the Airmega 400 matches the Blueair at 400, effectively tying it on that metric.

Yet the Airmega 400 is rated for 1,560 sq ft versus the Blueair's 635 sq ft. How can a lower CADR unit cover more than twice the room size? The answer is CADR vs room coverage ratings: the AHAM room coverage rating uses CADR at 1 air change per hour (ACH), the most conservative standard. The higher the CADR, the higher your base coverage. The Airmega 400's 1,560 sq ft rating reflects its specific motor and airflow design optimised for wide distribution, not just high particle removal rate.

In practical terms: for a 600 sq ft room, the Blueair delivers approximately 4 air changes per hour — double what AHAM requires and what asthma guidelines recommend. For a 1,000 sq ft room, the Blueair falls short of 2 air changes per hour. The Airmega 400 comfortably delivers 2+ ACH in a 1,000 sq ft space. The CADR advantage of the Blueair only matters within the room sizes the Blueair was designed to serve.

Room Coverage: The Number That Actually Matters Here

AHAM-verified room coverage ratings:

• Blueair Blue Pure 211i Max: 635 sq ft (AHAM standard, 2x air changes per hour)
• Coway Airmega 400: 1,560 sq ft (AHAM standard, 2x air changes per hour)

The Airmega 400 covers 2.5x more room area than the Blueair. This is not a marginal difference — it is a different product category. The 211i Max is a large-room purifier. The Airmega 400 is a very-large-room or open-plan purifier.

If you have a 650 sq ft room: the Airmega 400 is massively over-specified. The Blueair fits perfectly. If you have a 1,000 sq ft open plan: the Blueair is under-powered at 2 ACH. The Airmega 400 handles it with headroom. If you have a 1,200+ sq ft space: the Airmega 400 is the minimum recommendation. Nothing in the Blueair lineup covers it adequately.

Choose the Blueair if your room is under 700 sq ft. Choose the Airmega 400 if your room is 700-1,560 sq ft. This single question resolves the comparison for most buyers.

Noise: Near-Identical at Low Speed — Airmega 400 Quieter at High

Sleep mode / minimum speed: Coway Airmega 400 at 22 dB. Blueair 211i Max at 23 dB. Both are the quietest air purifiers in the large-room category and are effectively inaudible in normal bedroom conditions at minimum speed. The 1 dB difference is below the threshold of human perception and not a meaningful differentiator.

At medium speed: Airmega 400 approximately 38 dB vs Blueair approximately 40 dB. At maximum speed: Airmega 400 approximately 49 dB vs Blueair approximately 55 dB. The Airmega 400 runs quieter at higher speeds — its larger dual-fan design moves more air at lower RPM than the Blueair's single-motor design, reducing mechanical noise at equivalent airflow volumes.

For rooms large enough to require medium or high fan speeds for adequate air changes, the Airmega 400's noise advantage at those speeds becomes relevant. In a 1,000 sq ft space where the Airmega runs at medium to deliver 2 ACH, it does so at 38 dB. The Blueair at maximum in the same space would produce 55 dB while still delivering fewer air changes. This is where the Airmega's larger, more efficient airflow system justifies its price.

Energy Costs: Blueair Uses Less Power Per CFM

The Blueair 211i Max uses 46 watts at maximum speed for CADR 410 — an efficiency ratio of 8.9 cfm per watt. The Coway Airmega 400 uses 66 watts at maximum for CADR 328 (smoke/dust) — an efficiency ratio of approximately 5.0 cfm per watt. The Blueair is roughly 75% more energy-efficient per unit of clean air delivered on smoke and dust.

For rooms the Blueair is sized to handle (under 635 sq ft), the Blueair's lower wattage reduces electricity cost. Running 24/7 for a year at auto mode (averaging 40% maximum wattage): Blueair uses approximately 18 watts average, Airmega 400 approximately 26 watts average. Annual electricity cost difference at $0.15/kWh: approximately $10-12 per year in favor of the Blueair.

For rooms requiring the Airmega 400 (700+ sq ft), the comparison changes: you are not comparing the same room size. A single Blueair inadequately covering a 1,000 sq ft room running at maximum (46W) saves electricity but does not clean the air adequately. The Airmega's 66W correctly sized for the space is the better choice even if less efficient per cfm.

Filter Costs: Three-Year Analysis

Blueair 211i Max filter costs: Combination filter $45-60, replaced every 6 months. Washable pre-filter sleeve (never replaced). Three-year filter cost: $270-360 (six filter changes).

Coway Airmega 400 filter costs: The Airmega 400 uses a Max2 HEPA filter ($50-70) and a Max2 Activated Carbon filter ($40-50) replaced every 12 months. Three-year filter cost: $270-360 (three sets of two filters). Filter replacement cost over three years is nearly identical between units despite the Blueair replacing filters twice as often at half the individual cost.

Coway filter replacement is annual — easier to remember and manage than Blueair's semi-annual schedule. The Blueair pre-filter sleeve requires monthly washing that the Airmega does not have, adding minor maintenance overhead. The Airmega 400's larger filter surface area means less frequent blockage in dusty environments and more stable CADR over each filter's service life.

Three-year total cost of ownership: Blueair 211i Max $570-710. Coway Airmega 400 $720-960. The Airmega costs more over three years — approximately $150-250 additional — reflecting the higher unit price offset by similar filter costs. For rooms the Airmega is genuinely required for, that premium is the cost of correct sizing.