Coway Airmega 250 vs 400

Choose the Coway Airmega 250 for a room around 300 square feet with an 8-foot ceiling and a shallow place to put it; choose the Airmega 400 for a room around 400 square feet on the same sizing basis. At 500 square feet, the 400 only just meets the EPA's sizing estimate below, so consider more capacity if you want room to reduce fan speed. The 250 needs one Max2 cartridge; the 400 uses a pair, sold together as a complete replacement set.

Recommendations use Coway's published specifications and the EPA's room-sizing estimates. Official sources checked November 2, 2026.

Quick picks

• Choose the 250 when its output meets your room calculation and floor depth matters. Its front-access filter arrangement also suits a place where reaching both sides would be awkward.
• Choose the 400 when you need the higher published CADR and can leave both sides accessible.
• Choose 250S or 400S for app control and schedules. The S suffix adds connectivity; it does not raise the family's published CADRs.
• Return to the shortlist if neither fits: our best air purifiers includes the existing Mighty2 pick and other sizes. For a bedroom, also read quiet air purifiers for bedrooms.

Airmega 250 vs 400: the comparison table

Sources: Coway's 250/250S one-sheet, 400/400S one-sheet and the US manuals linked below. Coway's smoke CADRs are 249 for the 250 and 328 for the 400:

• Airmega 250249CFM
• Airmega 400328CFM

Source: Coway's US one-sheets; these are published ratings, not measurements by thisHUSH

A rating conflict: the EPA's current certification dataset lists AP-2015F smoke CADR 376.0 CFM and room size 583 sq ft, while Coway's one-sheet says 328. We cannot establish why. Our calculations consistently use Coway's lower figure; they are not AHAM certification listings.

Choose the Airmega 250 for the shallower footprint

Choose the 250 when the room calculation works and you want less depth projecting into the room. Its 18.5-inch width exceeds the 400's, so check both dimensions when shopping for a compact air purifier. The washable pre-filter pulls upward from behind the front cover; Max2 sits behind it.

Its Rapid Mode runs at the same maximum fan speed as manual level 3, according to the US manual. Rapid changes the operating sequence rather than adding maximum output.

Choose the non-Wi-Fi Airmega 250 at Coway.

Choose the Airmega 400 for more room-volume capacity

The 400 publishes higher CADRs for all three particle categories in the table. Its square base and 24.7-pound weight make it a purchase to place deliberately. Both side covers need to come off for filter service, and the manual says not to place it where both sides are blocked.

The complete purifier includes two pre-filters and two Max2 filters, according to Coway's listing. You do not need an extra set to complete a standard new unit. Before first use, remove the plastic wrapping from both installed Max2 filters, as the manual directs.

Choose the non-Wi-Fi Airmega 400 at Coway.

250 vs 250S, and 400 vs 400S

Coway's shared family specifications give the same CADRs to the base and S versions. On the S models, a Wi-Fi button takes the base model's timer-button position; the timer and scheduler are app functions. If you want a timer entirely on the purifier, choose the base version.

Check the network requirements separately: the revised 250/250S manual supports 2.4 GHz and 5 GHz connections, while the 400S listing says 5 GHz alone will not work. The 250 Art shares the replacement-filter family, but its membership there is not evidence that all its other specifications match the standard 250.

Size the room by volume, then compare CADR

Coway's 930- and 1,560-square-foot figures both use two air changes per hour. Its 400 one-sheet also advertises 3,120 square feet at one change per hour. Those figures describe different air-change rates from the 4.8 ACH basis explained by AHAM Verifide.

For the buying decision, use the EPA's published room-size estimates on an 8-foot ceiling basis. For a taller room, first calculate:

Equivalent area at an 8-foot ceiling = actual floor area × actual ceiling height ÷ 8.

The ceiling conversion is our arithmetic. The CADR estimates below are the EPA's rounded chart values, not newly assigned AHAM room ratings.

The EPA's sizing guidance says to size up for high ceilings or an open floor plan and notes that CADR is typically measured at the highest speed. Count the connected space you intend to serve. A quieter fan setting needs its own output evidence; do not transfer the headline CADR to Sleep Mode.

1. 1

   Measure the connected area

   Multiply room length by width; include adjoining open space you want served.

2. 2

   Include ceiling height

   Use the volume formula above rather than comparing maximum-area headlines.

3. 3

   Allow output headroom

   If the calculation nearly uses the published CADR, consider greater capacity before planning slower operation.

Floor space, intake access and moving it

There is a small dimensional conflict on the 250: Coway's one-sheet gives 8.3 inches of depth, while its revised US manual gives 8.03 inches. Both give 18.5 inches of width and 19.7 inches of height. For planning, allow the larger published depth and room to remove the front cover and pull the pre-filter upward.

The 400's 14.8 × 14.8-inch base needs access on both sides. The revised manuals require unobstructed airflow and a firm, flat, dry surface; chassis dimensions are not the whole usable placement space. Keep the top outlet clear. We do not assign an invented intake-clearance distance where these manuals give no numeric intake minimum.

The 250 is 20.5 pounds, versus 24.7 pounds for the 400. Consider that lift before planning daily moves.

Lights, noise and automatic modes

Both have physical light controls. The 250 manual describes a sequence that turns the air-quality indicator off, then all indicators off, then indicators back on. The 400's Light button switches its air-quality indicator and light on or off. Use those controls when the issue is illumination rather than changing the fan mode solely to darken the unit.

Both offer Smart/Auto, Sleep and Eco operation. Their revised manuals say automatic Sleep needs darkness and good sensed air quality for three minutes. Eco can stop the fan after the sensed level remains good for more than ten minutes; manual speed selection is the more predictable choice if you want continuous airflow.

Coway's 22–54 dB(A) and 22–52 dB(A) ranges do not establish a winner at matched output.

The exact replacement-filter order

Both families combine activated carbon and HEPA in Max2 cartridges, with separate washable pre-filters. Here is the complete routine Max2 order, using the SKU field in Coway's current store data, not a purifier model number:

The manufacturer's current data also identifies those orders with barcode fields 00003109144 and 00003104756, respectively. Keep the family name and pack contents alongside any identifier when comparing offers. The word “set” alone is not a reliable cartridge count: Max2 itself combines carbon and HEPA.

The 250 manual says to clean its pre-filter approximately every two weeks and replace Max2 approximately every twelve months, both based on eight hours daily at maximum speed. Actual runtime and speed affect the interval. The 400 one-sheet also lists a year, while its manual directs replacement when the Max2 Change indicator lights. Follow the indicators and the manual supplied with your unit.

• Yes: Match the exact model family before ordering
• Yes: Count the complete retail set when comparing ongoing costs
• Yes: Wash and fully dry the reusable pre-filter before reinstalling
• No: Do not wash or reuse the Max2 cartridge

A running-cost worksheet without stale prices

Compare complete replacement events, not individual cartridges. Let F be the current delivered cost of the correct retail item above and N the number of complete changes you expect annually. Your filter allowance is F × N. For the 400, F already covers the pair; do not multiply the complete set's cost again just because the machine has two sides.

For electricity, enter your hours per day H, operating days D, and local cost per kWh R:

• 250 nameplate scenario: 64 ÷ 1,000 × H × D × R.
• 400 nameplate scenario: 66 ÷ 1,000 × H × D × R.

These use Coway's published power-consumption figures. They are budgeting scenarios, not measured annual bills or predictions of Auto/Eco consumption. Add the electricity scenario to F × N, and check any subscription terms separately if you choose recurring filter deliveries. A cartridge count alone cannot make either purifier the “best air purifier with cheap replacement filters.”

How we choose

This comparison uses specifications and manuals, without physical testing. We checked Coway's US one-sheets, revised manuals and store data for models, contents and compatibility. AHAM and EPA guidance inform the common sizing calculation. We disclose the conflicting EPA certification data; current AHAM directory rows for these exact models were not independently confirmed.

Our broader approach is on How we choose. For a different room or chassis size, return to best air purifiers.

Verdict

Buy the 250 when the volume calculation fits and you value shallow depth and front filter access. Buy the 400 when the room needs its higher published CADR and you can service both sides. Choose an S version for connected controls, and compare ongoing filter costs using the exact complete replacement order above.

Sources

• Coway: 250/250S US one-sheet and revised US manual.
• Coway: 400/400S US one-sheet and revised US manual.
• Coway's 250 replacement catalog data and 400 replacement catalog data identify the exact order and current SKU fields.
• AHAM's ACH explanation and the EPA's air-cleaner guide.