Blueair model comparison

Blue Signature Small vs Medium vs Large: room rate, footprint and filters

The Blueair Blue Signature family currently offers three room-purifier sizes: Small SP1i, Medium SP3i and Large SP4i. Their Nordic Fog and Midnight versions are separate finish offers within each size; color does not change the model's airflow rating or filter size. Compare the published repeated-cleaning figures on the same 4.8-air-changes-per-hour (ACH) basis before reading the much larger one-hour headlines.

Choose the room rate before the furniture style

Blueair lists the Small at 248 square feet at 4.8 ACH, the Medium at 498 square feet and the Large at 705 square feet. The pages separately advertise 1,190, 2,250 and 3,385 square feet cleaned in an hour. Those latter numbers describe a slower, one-hour cycle; they are not equivalent substitutes for the faster 4.8-ACH area. Use the rate that reflects your room's regular operation, and leave margin if the room is open to a hall, has high ceilings or requires quiet low-speed use.

The Large page gives pollutant-specific CADRs of 450 CFM pollen, 434 dust and 455 smoke. Medium's page lists its own values; do not assume a single family CADR or treat one pollutant figure as universal. For an exact room threshold, the finder now exposes a numeric 4.8-ACH field and leaves unknown values out rather than promoting a one-hour headline.

Compare the shape, not just the height

Small is the easiest body to tuck beside furniture at 13.7 inches high and 9.4 inches wide and deep. Medium is taller and narrower, listed at 19.3 by 11.7 by 11.7 inches. Large is lower but broadest at 17.2 by 15.5 by 15.5 inches. That makes the Large a wider footprint rather than simply a taller tower. Preserve the manuals' required clearance around the intake and outlet; body measurements alone do not define the opening a shelf or wall must leave.

All three share a textile-wrapped, tabletop-style design, but the product-page and manual outlet descriptions should be checked for the exact size. None should be treated as an adjustable directional room fan unless its exact manual documents that function. Small and Medium have their own control/sensor and sound details; Large has a local PM2.5 readout, Auto and Night functions, and connected app features. For the Large SP4i, app pairing uses Bluetooth initially and a 2.4-GHz Wi-Fi network. A strict dB(A) limit remains unconfirmed because the page's 23–55 dB range does not identify A-weighting.

Keep filter size and finish straight

Each model uses a size-specific wrapped particle-and-carbon cartridge and washable textile pre-filter. A Large cartridge is not established as compatible with the Medium or Small. The standard fabric cover is included in the matching finish; alternate covers are separately sold. The Large's exact accessories list six pre-filter colors, while the Small's separately listed chrome ring base is an accessory rather than another purifier. Filter interval estimates vary with use and indoor pollution, so budget for replacement rather than treating an “up to” life claim as a guarantee.

Which one belongs on the shortlist?

Pick Small when its 248-square-foot 4.8-ACH rating and compact body fit the task. Medium moves the same design to a 498-square-foot rating with a narrower 11.7-inch footprint than Large. Large is the higher-capacity choice at 705 square feet, but it needs more floor width and a correspondingly larger filter budget. If the room exceeds a model's stated repeated-cleaning figure, do not justify it with the one-hour headline. If an essential need is exact gas sensing, a switchable ionizer, directional fan airflow or certified dB(A), confirm it from the exact size's manual rather than assuming family-wide features.

Sources: the exact Small SP1i, Medium SP3i and Large SP4i manufacturer pages and their size-specific manuals, filters and offer records. Product imagery in the reviews is official manufacturer render photography, not an independently tested unit.