Blueair 211i Max vs 311i Max vs 511i Max: these names are one digit apart and they are not the same machine. Here is the part that catches people out — the bigger number is the smaller purifier. The 211i Max is the largest and covers the most floor area; the 511i Max is the smallest and the cheapest. The numbering runs backwards from what you would expect.
Every figure below is Blueair’s own, taken from the three current Amazon listings. We have not had these units in a room.
The collision, in one table
Match the machine to the room and the decision is nearly automatic. Blueair states two coverage figures for each unit — a fast clean of a smaller area in about 12.5 minutes, and a larger area cleaned in one hour.
| 211i Max | 311i Max | 511i Max | |
|---|---|---|---|
| Amazon price | $262.99 | $229.00 | $99.99 |
| Cleans in 1 hour, up to | 3,235 sq ft | 2,107 sq ft | 1,138 sq ft |
| Cleans in ~12.5 min | 674 sq ft | 439 sq ft | 237 sq ft |
| Stated noise | not stated on listing | 23–50 dB, QuietMark certified | as quiet as 19 dB |
| Stated particle claim | not stated on listing | 99.97% down to 0.1 microns | 99.97% down to 0.1 microns |
| Filtration | HEPASilent dual | HEPASilent dual | HEPASilent dual |
| App, sensors, auto mode | yes | yes | yes |
| Cost per sq ft/hour | $0.081 | $0.109 | $0.088 |
Prices, coverage and noise figures are Blueair’s, from the Amazon listings at the time of writing. The bottom row is our arithmetic on Blueair’s numbers: price divided by the stated one-hour coverage. Two cells read “not stated on listing” because Blueair does not publish those figures for the 211i Max — that is missing data, not a zero, and we are not going to borrow a sibling’s number to fill the gap.
Notice the last row, because it inverts the usual advice. The 211i Max is the cheapest of the three per square foot despite having the highest sticker price, and the 311i Max is the most expensive per square foot despite sitting in the middle. Buying “the middle one to be safe” is the one move the numbers do not support.
Blue Pure 211i Max — the big open-plan one
$262.99. Blueair rates it for 674 sq ft in 12.5 minutes and 3,235 sq ft in one hour, and describes it for large living rooms, open floor plans, apartments and shared spaces.
This is the one to buy if your problem is a room that connects to other rooms. Open-plan kitchens and living areas do not have a door to close, so a purifier sized for a bedroom just circulates a fraction of the air. It is also, per the arithmetic above, the best coverage-per-dollar of the three.
The honest caveat: Blueair does not publish a decibel figure or the 99.97% particle claim on this listing, though it does list the same HEPASilent dual filtration as the others. If a specific noise number matters to you — because it will run in a room you sit in all evening — get it from Blueair before you buy.
Blue Pure 311i Max — the medium one
$229.00. Blueair rates it for 439 sq ft in 12.5 minutes and 2,107 sq ft in one hour, for bedrooms, living rooms, apartments and home offices.
This model has the most complete published spec of the three. Blueair states HEPASilent dual filtration capturing 99.97% of airborne particles down to 0.1 microns, and QuietMark-certified operation between 23 and 50 dB. If you want a documented noise range and a documented filtration figure in writing before you spend, this is the listing that gives you both.
The catch is the one the table exposes: at $229.00 for 2,107 sq ft, it is the worst value per square foot here. You are $33.99 below the 211i Max and giving up 1,128 sq ft of stated hourly coverage. Buy it for the published specs and the size fit, not because it looked like the sensible middle.
Blue Pure 511i Max — the bedroom one
$99.99. Blueair rates it for 237 sq ft in about 12.5 minutes and 1,138 sq ft in one hour, and pitches it for bedrooms, nurseries, home offices, apartments and dorm rooms.
The spec that earns its place is noise: Blueair says it operates as quietly as 19 dB, the lowest stated figure of the three by a clear margin. For a machine that runs beside your head for eight hours, that number is arguably more important than coverage. It carries the same 99.97%-down-to-0.1-microns claim as the 311i Max and the same HEPASilent dual filtration.
At under a hundred dollars this is also the low-risk way into the range. If you are not sure an air purifier will do anything for your allergies, find out here rather than at $262.99.
Which one should you buy
Buy the 511i Max ($99.99) for a bedroom, nursery, dorm or small office — anywhere a door closes and quiet matters more than raw throughput. The 19 dB figure is the reason.
Buy the 211i Max ($262.99) for an open-plan living space, a large living room, or a home where one machine has to cover connected rooms. It is the highest stated coverage and the lowest cost per square foot.
Buy the 311i Max ($229.00) when a medium closed room is the actual target and you want the fullest published specification — the documented 23–50 dB QuietMark range and the stated 99.97% filtration — rather than the best value per square foot.
A note on the fourth sibling: Blueair also makes a 411i Max. We have deliberately left it out, because at the time of writing the only 411i Max listing we could confirm was a two-pack, and we will not compare a multi-pack price against three single units. If you specifically want the 411i Max, verify you are looking at a single-unit listing before you order.
Frequently asked questions
What is the difference between the Blueair 211i Max and the 311i Max?
Coverage and published specs. Blueair rates the 211i Max at 3,235 sq ft in one hour versus 2,107 sq ft for the 311i Max, and the 211i Max costs $262.99 versus $229.00. The 311i Max, however, publishes a noise range (23–50 dB, QuietMark certified) and a filtration figure (99.97% down to 0.1 microns) that the 211i Max listing does not state.
Is a higher Blueair number a better air purifier?
No, and this is the single most common mistake with this range. The numbering runs backwards: 211i Max is the largest, 311i Max is medium, 511i Max is the smallest. Read the coverage figure, not the model number.
Which Blueair Blue Pure Max is best for a bedroom?
The 511i Max, on Blueair’s own stated numbers. It is rated for 1,138 sq ft in an hour, which is more than enough for a bedroom, and Blueair states it runs as quietly as 19 dB — the quietest of the three.
Do the 211i Max, 311i Max and 511i Max use the same filter?
Do not assume they do. These are three physically different sizes of machine, and the Amazon listings do not state a shared filter part number. Buy the replacement filter listed for your exact model rather than the one for the range — the names are close enough that ordering the wrong one is easy.
What do the Blueair 211i Max, 311i Max and 511i Max cost?
$262.99, $229.00 and $99.99 respectively on Amazon at the time of writing. Air purifier prices move often, so confirm the current figures.
Is the 511i Max too small for a living room?
It depends on the room and whether it is closed off. Blueair rates the 511i Max at 1,138 sq ft in one hour, which covers plenty of ordinary living rooms. For an open-plan space that flows into a kitchen or hallway, the 211i Max’s stated 3,235 sq ft is the safer specification.
The short version
The names are the hardest part of this decision, and they are hard for one reason: the number goes up as the machine gets smaller. Once you know that, the range is straightforward. Measure the room, read Blueair’s one-hour coverage figure, and pick the model that clears it — 511i Max for a bedroom, 211i Max for an open plan, 311i Max when you want the fullest published spec sheet for a medium closed room.
And if you take one number away from this page, make it the bottom row of the table: the most expensive model is the cheapest per square foot, and the one in the middle is the priciest. That is the opposite of how these ranges usually work.
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