Blueair model fit
Blueair 511i Max or 311i Max? Compare small-room fit at 4.8 ACH
The Blue Pure 511i Max is the compact end of Blueair’s reviewed Blue Pure Max choices. Its current U.S. page lists 237 square feet at 4.8 air changes per hour; the 311i Max and 311i+ Max list 439 and 525 square feet, respectively, at the same rate. The right choice is the smallest one that fits the actual room at the rate you want—not the model with the biggest one-hour interval claim.
| Model | Current U.S. 4.8-ACH area | Body, H × W × D | Listed input | On-unit feedback |
|---|---|---|---|---|
| Blue Pure 511i Max | 237 ft² | 14.5 × 9.3 × 9.3 in | 17 W | Five-color PM2.5 status |
| Blue Pure 311i Max | 439 ft² | 19 × 12.5 × 12.5 in | 32 W | Five-color PM2.5 status |
| Blue Pure 311i+ Max | 525 ft² | 21 × 12.5 × 12.5 in | 38 W | Five-color PM2.5 status |
Choose the 511i Max for a bedroom or office that fits its current repeated-cleaning rating and where a compact footprint matters. If the enclosed room is larger, the 311i Max offers more listed area while staying shorter than the 311i+ Max. The Plus model adds listed capacity but keeps the 12.5-inch width and depth, so height is not the only clearance dimension. Leave intake and outlet space around any model; the dimensions above are the shell, not an airflow clearance plan.
Do not compare different cleaning intervals as if they were equivalent
Blueair’s 511i Max page also says 569 square feet in 30 minutes and 1,138 in an hour. Those slower intervals correspond to fewer air changes than the 237-ft²-at-4.8-ACH figure. The 311i Max and 311i+ Max pages likewise show larger-area claims at slower intervals. If your decision depends on repeated room cleaning, compare the explicit 4.8-ACH figures. For an open plan, a connected kitchen/living room, or a high ceiling, no flat square-foot number guarantees that every part of the space sees the same cleaning rate.
The published room-area record is not perfectly tidy. The current 511i Max page gives 237 ft² at 4.8 ACH and says its values reflect a DOE update; its title still contains 465 ft², and Blueair’s May 2026 support table lists 194 ft². The 311i Max title similarly differs from its current detailed 439-ft² entry. For the rows above, the explicit detailed rate-labeled product-table values were selected, and the older competing figures remain documented in each model’s full review. These are manufacturer claims, not independent room tests.
Sensor display and filter differences still matter
All three reviewed models offer Auto mode and app functions with local buttons. Their manuals describe PM2.5-driven Auto mode and a five-color status indicator rather than a numeric on-unit reading. If you need a displayed particle number at the machine, compare the reviewed 211i Max instead; a color light is not a less precise version of a number. A PM2.5 sensor also does not identify an odor or gas.
Filter identities are model-specific. The 511i Max’s exact F5MAX page names it as the only compatible purifier and lists Particle & Carbon, AllergenBlock and SmokeBlock options. The 311i+ Max has a different named F3MAX+ page. The non-plus 311i Max’s own filter page contradicts itself on compatibility, so its replacement fit is still a question for Blueair rather than an assumption that the cartridges are interchangeable. Specialty filters are separate purchases; the one-unit purifier box includes its basic main filter and fabric pre-filter.
If 237 square feet at the desired rate is sufficient, the 511i Max is the smallest body of these three and the lightest in their listed dimensions. If it is not, do not make the 1,138-square-foot one-hour claim do the work of a higher repeated-cleaning rating: move up to a 311i model whose explicit 4.8-ACH area fits the room. Compare the long reviews for the 511i Max, 311i Max and 311i+ Max before deciding; neither conflicting dB endpoint nor pollutant-specific CADR should be treated as a verified generic limit.
Sources: Blueair’s exact U.S. product pages and model-specific English manuals for the Blue Pure 511i Max, 311i Max and 311i+ Max, plus the exact 511i Max F5MAX replacement-filter page. Room rates, shell measurements and filter identifiers are tied to those specific configurations; no independent performance tests are claimed.