The Blueair Blue Signature Large and the Blueair Blue Pure 211i Max clean almost exactly the same size room, so the Signature's extra cost buys looks and better odor filtration, not more clean air. Buy the 211i Max unless guests will see the purifier every day or cooking and pet smells are the main thing you are trying to fix.
The short answer
Choose the Blue Signature Large if it will stand in a room people see, you want a low drum you can rest a lamp or book on, odors matter as much as dust, and you prefer one filter change a year.
Choose the Blue Pure 211i Max if the purifier is going in a corner or behind a sofa, your problem is particles (pollen, dust, smoke haze), and you would rather spend about $100 less.
| On paper | Blue Signature Large (SP4i) | Blue Pure 211i Max |
|---|---|---|
| Smoke / dust / pollen CADR | 455 / 434 / 450 CFM | 435 / 452 / 450 CFM |
| Sized for (4.8 air changes an hour) | ~705 sq ft | ~674 sq ft |
| Blueair's noise figures | 23 to 55 dB | 23 to 53 dB |
| Rated power | 3.5 to 42 W | 46 W max |
| Height x width | 17.2 x 15.5 in | 22.7 x 14.4 in |
| Weight | 13.2 lb | 16.2 lb |
| Carbon | Pelleted, inside the wrap filter | Carbon layer Blueair pitches for light odors |
| Main filter | $99.99, up to 12 months | $69.99, up to 9 months |
| Price | $449.99 list, $337.49 on sale | $349.99 list, seen at $227.99 |
| Warranty | 1 year, 3 with registration | 1 year, 3 with registration |
The room-size math, done properly
On the rated numbers the Signature covers about 31 sq ft more, a difference under 5%. Look past smoke CADR and the gap closes or flips: the 211i Max rates higher on dust (452 vs 434 CFM) and the two tie on pollen at 450. For an allergy household, nothing in the CADR table argues for the pricier model.
Some real rooms:
- 22 x 30 ft combined kitchen and lounge (660 sq ft): about 5.2 air changes an hour at top speed for the Signature and 4.9 for the 211i Max. Both clear the bar, barely.
- The same footprint with 9 ft ceilings: coverage drops to about 627 and 599 sq ft, so both fall just short at full power.
- 10 ft ceilings: about 564 and 539 sq ft.
Full coverage only happens at the loud top speeds, though, so the more useful figure is how much each cleans while staying quiet. HouseFresh measured the Signature delivering 229 CFM while under 45 dBA. RTINGS, as reported second-hand, puts the 211i Max at about 224 CFM on speed 2 under the same 45 dBA line. Those work out to roughly 355 and 347 sq ft at 4.8 air changes. Two labs, two methods, one conclusion: for everyday quiet running, both are 350 sq ft machines that can sprint to 700.
That makes a 15 x 22 ft living room (330 sq ft) the sweet spot for either, running on speed 2 most of the day. Size your own space with the room size calculator.
What the Signature's premium actually buys
Real carbon. HouseFresh's teardown found loose pelleted activated carbon inside the Signature's wrap-around filter and rated it well above the carbon-treated fabric Blueair uses elsewhere. Blueair describes the 211i Max standard filter as being for light household odors. Frying smells and litter boxes are gas problems, and gases are the carbon's job, not the particle media's; the activated carbon explainer covers the mechanics. Blueair's "OdorFence" claim of 10x odor removal is its own, unverified figure.
A filter that lasts a year. Blueair rates the Signature filter for up to 12 months; HouseFresh quotes 9 to 12 as Blueair's guidance.
A sensor that leaves you alone. HouseFresh notes the Signature's laser particle sensor doesn't need routine cleaning. Its top-mounted touchscreen wakes when you wave a hand and goes dark after a few seconds, with brightness set in the app.
Furniture proportions. At 17.2 inches tall and 13.2 lb it is shorter and lighter than the 211i Max, and the top takes light objects. Blueair's guidance, as reported by reviewers, caps that at 11 lb with no liquids or hot items.
Very low draw at a sensible speed. On speed 2, HouseFresh's meter read 6.63 W with the sound level around 40 dBA.
Where the 211i Max is the smarter buy
Price. At list the gap is $100; at the sale prices seen this autumn ($337.49 against $227.99) it is about $110.
Filter choice. The 211i Max takes four versions of its filter, including SmokeBlock ($84.99), which Blueair says doubles the activated carbon, and AllergenBlock ($89.99). The Signature Large has a single filter. A 211i Max owner can switch to SmokeBlock for wildfire season and back again.
Floor space. It is narrower at 14.4 inches, which helps in a tight corner.
No accessories to budget for. The Signature's styled look depends on optional legs (about $87, per HouseFresh) or a chrome ring base (about $100).
Filter and three-year cost
Assumptions: list prices, the filter in the box covers the first interval, electricity counted separately.
| Three years | Blue Signature Large | Blue Pure 211i Max |
|---|---|---|
| Purchase | $449.99 | $349.99 |
| Filters at the longer interval | 2 x $99.99 = $199.98 (12 months) | 3 x $69.99 = $209.97 (9 months) |
| Filters at the shorter interval | 3 x $99.99 = $299.97 (9 months) | 5 x $69.99 = $349.95 (6 months) |
| Total, longer interval | $649.97 | $559.96 |
| Total, shorter interval | $749.96 | $699.94 |
So the $100 sticker gap narrows to about $90 if both filters reach their full rating, and to about $50 if both wear out early. Year by year the filter spend is nearly level: roughly $100 to $133 on the Signature against $93 to $140 on the Blue Pure. Running the 211i Max on SmokeBlock at nine-month intervals adds roughly $45 over three years, putting it within about $45 of the Signature.
Electricity barely separates them. At their rated maximums, 42 W and 46 W around the clock come to about $63 and $69 a year at $0.17/kWh. Rerun the filter numbers with your own intervals in the filter cost calculator.
Details buyers miss
- Air leaves the Signature from the side. Plan placement so it doesn't blow across a bed or desk.
- Neither has an off switch for the ionizer. Both use Blueair's HEPASilent charging stage. The Signature carries an AHAM ozone certification of 3 ppb according to HouseFresh, under the 5 ppb line used for ozone-free claims; no matching certified figure for the 211i Max turned up in research.
- Name drift. Amazon calls the Large "Signature SP4i"; launch coverage just said "Blue Signature." The Medium (SP3i) and Small (SP1i) are different machines with different filters.
- Both are loud flat out. HouseFresh measured the Signature at 59.6 dBA on top speed; RTINGS' reported top figure for the 211i Max is about 58.7 dBA.
- Track record. The Signature launched in June 2025, so there is less owner history behind it.
Which one to buy
For most homes, the 211i Max: same particle cleaning, a wider filter menu, and roughly $100 kept in your pocket. Pay for the Blue Signature Large when it will be on display and odors are a daily problem, since the pelleted carbon is a genuine functional upgrade and not only a styling one.
If your room is nearer 500 sq ft, the Signature Medium (SP3i, $299.99, 321 CFM) is the design pick at a lower price. And if an always-on ionizing stage rules both Blueairs out, switch to the Levoit Core 600S: no charging stage at all, 410 CFM, and a room size of roughly 606 sq ft.
Frequently asked questions
Does the Blue Signature Large filter fit the 211i Max?
No. The Signature Large uses its own $99.99 filter, and Blueair's F2MAX filters fit only the Blue Pure 211i Max. The Signature Small and Medium each take their own size-specific filter too.
Is the Blue Signature Medium enough instead of the Large?
For rooms up to about 500 sq ft, probably. Blueair lists the Medium (SP3i) at 321 CFM smoke CADR and $299.99, which sizes to roughly 498 sq ft at 4.8 air changes an hour. Above that, the Large or the 211i Max is the right size.
Which way does the Blue Signature blow air?
Out of the side, according to Blueair's spec table, which is unusual for a round purifier. Point the outlet away from a bed or desk chair if you dislike a draft.
Do you need the legs or base for the Blue Signature?
No, they are optional accessories that raise it to side-table height. HouseFresh lists the wooden legs at about $87 and the chrome ring base at about $100, so add that to the price if the styled photos are what sold you.
Can a SmokeBlock filter make the 211i Max as good on odors as the Signature?
It narrows the gap on paper, since Blueair says SmokeBlock carries twice the carbon of the standard 211i Max filter. No published teardown compares its carbon with the Signature's pellets, so treat it as an improvement, not an equal.