Comparisons
Coway Airmega 450 vs 400 vs ProX
The Coway Airmega 450, 400 and ProX all target larger rooms, but they are not interchangeable by headline area. The 450 is the non-S model with a numeric particle display, wheels and one 3-in-1 filter assembly; the 400 is an app-free model with color-category feedback and two-sided Max2 filters; the ProX is the biggest of this trio and has numeric particle readings. Compare the same cleaning rate and the capabilities you will actually use.
How much usable room does each number represent?
Coway lists the 450 at 1,643 square feet at two air changes per hour and the 400 at 1,560 square feet at that rate. The ProX is listed at 2,126 square feet at two ACH. At a common 4.8-ACH comparison, those become about 685, 650 and 885 square feet, respectively, by multiplying each two-ACH figure by 2 ÷ 4.8. These are calculations, not direct 4.8-ACH manufacturer ratings. The 450 therefore adds only about 35 square feet over the 400 in this comparison; do not pay for a bigger model unless you need its display, filter layout or extra rated area. The ProX provides a more noticeable room-size step, but it is also a much larger, heavier cabinet.
The single-air-change figures—3,285 square feet for the 450, 3,120 for the 400 and 4,253 for the ProX—describe much slower air turnover. They should not be substituted for a repeated-cleaning requirement. High ceilings, open doorways, furniture, placement and the fan level used can all affect practical fit. The 450 manual's 821 square feet in 15 minutes is another manufacturer-stated rate format; preserve it separately rather than presenting it as a guarantee for an open plan.
Choose the feedback and controls you need
The 450 manual documents on-unit numeric PM1.0, PM2.5 and PM10 readings in addition to a four-color category indicator. The 400 shows a color category, not a numeric PM2.5 value. The ProX offers numeric particle readings and a display. None of these particle sensors should be treated as a confirmed TVOC or general gas monitor simply because the filters use activated carbon.
The plain 450 and 400 are local-control models. Coway's combined 450/450S manual marks app and Wi-Fi setup for the distinct 450S; those functions do not belong to the non-S 450 offer. If an app is essential, compare a different exact configuration such as the reviewed Levoit Core 600S-P instead of relying on a shared manual. The ProX is also not an app-enabled option in its reviewed plan.
Filter work is part of the fit
The 450 uses one generic 3-in-1 assembly with a vacuumable pre-filter, Green True HEPA and activated carbon. Coway lists Fresh Starter+, Allergen+ and Intense Smoke+ as separately sold replacement choices; the machine's color-only offer record does not establish which custom profile is included in every box. Its manual calls for vacuum or dry-cloth pre-filter care every two to four weeks and full-filter replacement about annually under an eight-hours-per-day Turbo example, with actual life depending on conditions.
The 400 instead has two washable pre-filters and two paired Max2 filters, one on each side. This can mean more access around the cabinet and two filter elements to replace together, but its pre-filters can be washed and shade-dried according to its manual. The ProX also uses paired, side-access filters and four locking casters, with an even bigger body to position. Check the separate review for exact filter costs and fit details; do not infer that one design is cheaper from filter count alone.
Check dimensions before committing
The 450 weighs 24.9 pounds and has wheels, but its product page lists a 13 × 13 × 29-inch body while its linked manual says 13.4 × 13.4 × 29.6 inches. Treat strict body dimensions as unconfirmed; a tight alcove is a poor fit until the delivered model is measured. Its manual also warns that the narrow wheel gap may not roll smoothly on carpet or uneven flooring. The 400's documented body is 14.8 × 22.8 × 14.8 inches and 24.7 pounds. The ProX is substantially heavier and larger; its casters help across one level floor, not up stairs.
Choose the 450 for a large room where roughly 685 square feet at a 4.8-ACH comparison rate is adequate, a local numeric particle display matters, and physical control is acceptable. Choose the 400 when a color indicator is enough and the two-sided washable-prefilter arrangement suits your care routine. Step up to ProX when you need more room margin and can accommodate its larger cabinet. If an app, a verified tight body measurement, a generic CADR value, or a dedicated gas reading is essential, none of the three should be selected on an assumption.