No: the airflow rating on the box is typically measured at the highest speed, and the low decibel figure describes the slowest.
CADR, the clean air delivery rate, is the standard measure of how much filtered air a purifier delivers. AHAM, which runs the Verifide certification program, says the higher the CADR, the faster the unit filters the air.
The EPA adds the detail that matters here: the rating is typically measured at the air cleaner's highest speed. Its technical summary goes further. Ratings are determined at maximum airflow, and therefore typically at maximum noise. At lower settings, the EPA says, the CADR may not be known, and it could be considerably lower than the advertised figure.
The low decibel figure, meanwhile, describes the slowest speed. So the two headline numbers never describe the same moment.
Three makers publish enough to show the gap:
- IKEA STARKVIND: 29.4 CFM at 24 dB on its lowest speed, and 141 CFM at 51 dB on its highest, with both filters.
- Alen BreatheSmart 35i: 66 CFM at speed 1, rising to 190 CFM on Turbo. Our Alen air purifier decibels page lists the airflow and both labelled figures for all five current Alen models.
- Rabbit Air MinusA2: 58 to 218 CFM across its range. Rabbit Air also prints a dBA figure for each of its five fan speeds, and our Rabbit Air purifier decibels page lists them for every current model.
How many decibels is an air purifier?
Air purifier decibels depend on the speed: Blueair lists 19 dB low and 46 high for the 411i+ Max, and the EPA says a noise rating around 50 decibels is roughly the operating noise of a modern refrigerator.
Medify: 19.8, 37 and 49.3 dBA for the MA-25. Medify does the same for all six purifiers it sells in the US, and our Medify air purifier decibels page lists every one, speed by speed.
Rabbit Air does too, as noted above, and so does IQAir, on all seven of its room and desk purifiers; our IQAir air purifier decibels page lists every model.
Both ends, labelled
Blueair (19 dB low and 46 high for the 411i+ Max), Alen (lowest and highest speed) and IKEA (lowest and highest fan speed).
A range, ends not labelled
Coway (20 to 48 dB(A) for the Airmega 100) and Levoit. Levoit has a page of its own: our Levoit air purifier decibels page lists every current model and shows the three where Levoit ties the low end to Sleep Mode and the three where it names the lowest fan speed.
The slowest speed only
Winix, at 23.5dB for the 5510.
Nothing on the product page
Honeywell, for the model we read.
Of the makers behind the fifteen purifiers we read, none states a measuring distance or names a test standard for its figure. IQAir does both: on four models it says the figures are sound pressure "at 3.3 ft distance", and it cites EN ISO test standards.
AHAM says a separate standard exists for measuring the sound of room air cleaners, but no maker page we read cites it. The EPA's own summary says noise is seldom reported in a standardized way, which makes devices hard to compare. So a decibel or two between Winix, Blueair, Medify and Alen is unknown, not a ranking.
Two makers contradict themselves. Blueair's 511 page lists 24 to 49 dB in its spec table and 22 to 44 in its FAQ. Levoit's Core 400S page says 22 dB in one place and 24 in another. We quote both and do not rank either on the lower figure.
The 511 is not alone: our Blueair air purifier decibels page lists all 20 current Blueair models with a figure and flags six product pages that give one figure in the spec table and another in the FAQ.
For scale, the EPA says a noise rating around 50 decibels is roughly the operating noise of a modern refrigerator. Most top speeds here are close to that. Our decibel chart sets figures such as Medify's 19.8, 37 and 49.3 dBA beside a whisper, a fridge hum and conversation.
What size air purifier do you need?
AHAM's rule of thumb is that the smoke CADR should be at least two-thirds of the room's area, and a unit rated above that can run on a quieter setting. Sizing up and running it on low is the practical answer to the trade-off, and the official sources support it.
Start with the room. A 10 by 12 foot room is 120 sq ft, so it wants a smoke CADR of at least 80. The EPA's sizing chart, for an 8-foot ceiling, gives 130 CFM for 200 sq ft and 195 for 300.
For wildfire smoke AHAM asks for more, a smoke CADR equal to the room's area in square feet, and our guide to the quietest air purifier for smoke ranks purifiers on the noise at the speed that delivers that rating.
Then go bigger
The EPA says an air cleaner filters less air at a lower speed. AHAM says a higher CADR simply cleans the air more often and faster. So a unit rated well above your room can run on a quieter setting and still move a useful amount of air.
The Blueair 311i Max, rated for 439 sq ft, is our size-up pick. For living rooms and open-plan spaces, our large-room air purifier guide applies the same rule to bigger machines.
Compare room sizes on the same basis. AHAM's suggested room sizes assume 4.8 air changes per hour. Makers often headline a lower rate, which gives a bigger number.
Medify's headline 413 sq ft is at 2 air changes an hour; at 4.8 it is 172 sq ft. Alen's 700 sq ft for the 35i is also at 2; ENERGY STAR lists that model at 233 sq ft. Levoit prints both, which is the right way to do it.
If allergies are the reason you are shopping, size by the pollen and dust CADR rather than the room figure on the box; our air purifier for allergies guide ranks the certified units at the full speed those ratings describe.
What does sleep mode do on an air purifier?
In the manuals we read, sleep mode runs the fan lower, and some models dim their lights as well. A purifier's own lights and settings can matter as much as its fan.
Sleep modes.
Levoit's manual says its sleep mode uses a fan speed lower than low. Coway's manual says the Airmega 100's sleep mode lowers the fan and limits the buttons to half brightness.
Automatic dimming.
The Winix 5510 enters sleep mode when the room goes dark. Rabbit Air and Alen dim their lights in a dark room.
Auto mode can get loud.
Auto modes raise the fan when the sensor detects particles, as Rabbit Air describes. For a steady quiet level at night, choose a sleep mode or a fixed low speed.
Lights off.
Blueair and Levoit have night or display-off settings. IKEA's STARKVIND needs its app and a hub to switch the light off.
A low figure helps at night only if it belongs to the setting left on until morning, and most makers do not name that setting. Here is what each one says, in its own units.
Winix 5510.
The page gives 23.5dB for the slowest speed, and the manual sets Sleep Mode to the "minimum speed (lower than 'Low')", so that is the overnight figure. The page adds that light in the room switches Sleep Mode back to Auto Mode, which goes to high when the sensor reads poor air.
Blueair Blue Pure 411i+ Max.
The page lists "Low setting: 19 dB", and the manual counts four fan speeds, "Night mode being the lowest/most silent one". Whether that 19 dB belongs to Night mode or to speed 1, Blueair leaves unsaid.
Medify MA-25.
The manual names three fan speeds and no auto mode, so speed 1, 19.8 dBA, is the quietest setting it describes, and speed 2 jumps to 37 dBA. Medify labels its figures "dBA sound pressure".
Alen BreatheSmart 35i.
23 dB at the lowest speed, where Alen also gives the airflow: 66 CFM.
Levoit Core 200S-P.
Not one of our picks, but the only purifier we read whose maker ties its figure to the sleep setting in words: Sleep Mode runs "with noise levels as low as 27dB", below fan speed I with the display off. Levoit rates it for 140 sq ft at a rate of 4.8 air changes an hour.
Size for that setting, not the box. AHAM's two-thirds rule gives a 12 by 14 foot bedroom, 168 sq ft, a smoke CADR of at least 112.
At 4.8 air changes an hour the Medify is rated for 172 sq ft, the Alen for 233 (its ENERGY STAR listing), the Blueair 411i+ Max for 259 and the Winix for 392 (AHAM Verifide, per Winix). In that room the Medify would need its louder speeds to keep up; the other three can turn down.
If auto stays on overnight, Levoit's Core 400S manual describes a Quiet Auto Mode that holds medium speed "even when the air quality is poor, to avoid making too much noise." Where it stands matters too: Winix warns that "Flimsy or slanted surfaces may result in abnormal noise and vibrations."
How do you make an air purifier quieter?
To make an air purifier quieter, give it space, take the plastic off a new filter, clean the pre-filter and replace the filter when it is due.
Give it space. Levoit asks for 15 inches of clearance on all sides and a flat, stable surface. Coway asks for 20 cm from walls.
Remove the packaging
Levoit and Honeywell both tell owners to take the plastic wrap off a new filter.
Clean the pre-filter. Coway says every 2 to 4 weeks for the Mighty. Rabbit Air says every 3 months or as needed. Levoit says a pre-filter clogged with hair or lint blocks airflow.
With a shedding dog or cat that cleaning comes round faster, and our guide to the quietest air purifier for pets reads the manuals for pet modes, fur-catching pre-filters and auto modes that ramp up near a litter box.
Replace the filter when it is due. Levoit's manual lists increased noise as one of the signs.
In a nursery, what the manuals say about locks, covers and ozone
A nursery raises questions a decibel figure cannot answer: what small hands can press or open, what the maker says about tipping, and whether it states anything about ozone. We answer them from the makers' manuals and pages alone, and make no claims about babies or health.
Locks cover different things
Medify's manual says to hold the child-lock button for 3 seconds "and all functional buttons will be locked", the widest lock we read. Alen's 25i and 35i lock the touch panel with a 3 second hold, though the 35i manual adds that "A chime will indicate that the control has registered your touch."
Blueair's 411i Max manual says the unit "will continue to operate but the speed/mode button will be locked." Coway's Airmega 100 answers a press on a locked button "with a beep sound", and its manual says "lock is deactivated automatically" once the cord is plugged back in or the timer has switched the unit off.
Both Alen manuals list an "Auto-off safety feature when front cover is removed", and Rabbit Air's says "A childproof feature pauses air purifier operation when the front panel is removed." The other manuals we read describe no cut-off.
Tipping and placement
Blueair's manual says "Place the air purifier on the floor or a stable surface to prevent tipping" and "Do not sit on, stand, climb onto or hang from the appliance." Coway's says not to put the Airmega 100 "on a bed or against soft objects, such as curtains", and "Do not place the product near a humidifier". None of these manuals mentions a crib.
Alen's 25i page lists "Ozone 0 PPM" and "Ionizer No", and Levoit lists the Core 300-P as "Ozone Free". Winix and Rabbit Air each say the product "complies with the maximum allowable concentration of ozone of 0.050 parts per million by volume".
We found no ozone statement from Blueair, Medify or Coway for these models, which is a gap in what they publish, not a finding.
For a small nursery that points to the Alen 25i, whose A (AUTO) light setting turns the lights off "when the room is dark" and which ENERGY STAR lists for 150 sq ft.
The Medify locks the most and covers 172 sq ft at a rate of 4.8 air changes an hour, and the Blueair 411i+ Max covers 259 sq ft but locks only its speed button.
How much does an air purifier cost to run?
Mostly the filters: the makers' own prices here run from $25 to $54 a filter, while power at low speed is small. Filters are the ongoing cost, and the makers' own prices and intervals vary widely:
- About $25 to $30 a filter: the IKEA STARKVIND ($25, replaced within 6 months) and the Blueair 411i+ Max ($29.99, up to a year).
- About $40 to $55: the Coway Airmega 100 ($39.99 a year), the Blueair 311i Max ($44.99, up to 9 months) and the Alen 35i ($54, 9 to 12 months).
- The Medify MA-25 costs $49.99 a set but lasts 3 to 4 months, which makes it the most expensive to run here on its maker's interval.
If your budget stops at $100, our guide to the quietest air purifiers under $100 sets each budget unit's filter bill beside its noise figures, and finds that the filters often cost more than the purifier over a few years.
Power is small at low speed where makers publish it: about 2 W for the IKEA at its lowest setting, and as little as 0.9 W for the Alen 35i.
Does ENERGY STAR rate air purifier noise?
No: we searched the ENERGY STAR room air cleaner specification for noise, sound and decibel, and found none of them. It sets energy efficiency and an ozone limit.
An ENERGY STAR listing is still useful here, because it gives each model's CADR and room size on one basis. For the Alen 35i, that listing shows a smoke CADR of 150, where Alen's page says 190 CFM.
Where do shoppers for a quiet air purifier go wrong?
The five buying mistakes here are pairing the quiet figure with the airflow figure, trusting a headline room size, buying exactly the size of the room, leaving it on auto overnight and reading a bare range as a quiet unit.
They describe opposite ends of the machine.
Trusting a headline room size
Check the air change rate behind it, and prefer 4.8.
Buying exactly the size of the room
The unit will spend its life on the loud settings.
Leaving it on auto overnight
The fan rises whenever the sensor wakes it.
Reading a bare range as a quiet unit
Coway and Levoit do not say which speed each end of their ranges describes. Coway names the setting on only three of its 19 current Airmegas, and our page of every Airmega's noise range says which three.
Blueair's 19 dB and Medify's 19.8 dBA both come without a measuring distance, so neither can be called the quieter of the two; comparing decibel ratings from different makers needs a shared distance and method first.
The Blueair 311i Max runs from 23 dB on low to 50 dB on high, and how quiet is quiet enough in your bedroom decides how far above low you can let it run overnight.
Levoit's manual lists a clogged pre-filter and a filter that is due among the reasons a purifier gets noisier, so check both before working through why your appliance got louder.
