Blueair Blue Pure 511i Max review: the 5 numbers, and why 1,138 sq ft is not one of them

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The verdict, before the detail

For one bedroom, this is the quietest purifier you can buy at the money. For a sitting room, it is the wrong machine, whatever the listing claims.

The US list price is $139.99, roughly £110 here — check what it is actually selling for today.

Blueair's own recommendation is 237 sq ft, about 22 m². The product title says 1,138 sq ft.

Both figures are true. Only one of them answers the question you are asking.

What it is, and where it sits

Blueair is a Swedish brand, and the 511i Max is the small end of its range. It was designed around a bedroom rather than a whole floor.

US list price is $139.99. That sits below the Levoit Vital 200S-P at a US list of $189.99, and well under Blueair's own 311i Max at a US list of $229.99.

At 1.9 kg it is light enough to carry upstairs in one hand. Purifiers this quiet are not usually this small.

CADR174 pollen · 159 dust · 153 smoke cfmRoom237 sq ft (22 m²) at 4.8 air changes/hrNoise19–48 dB · QuietMarkPower17 WOzoneZero Ozone certifiedUS list$139.99

What it does well

19 decibels is below the background hum of a quiet room

A quiet bedroom measures about 30 dB. The lowest setting here is eleven decibels under that.

You stop registering it before you fall asleep, which is the whole point of the certification. QuietMark tested it for exactly this.

At full speed it reaches 48 dB. In a 22 m² room you will rarely have cause to go there.

17 watts is the cheapest thing in its class to leave running

Seventeen watts continuously works out at roughly 149 kWh a year. At a typical UK unit rate that is a little over £40 if it never switches off.

The Vital 200S-P pulls 50 watts and the 311i Max 32. This is a third of the first and half the second.

A purifier does nothing while it is off. The cheapest one to run has an advantage no spec sheet lists.

The electrostatic stage is Zero Ozone certified

HEPASilent pairs a mechanical filter with an electric charge on the particles. The charge lets the fan turn slowly, and the slow fan is why it reaches 19 dB.

Ionising usually invites an ozone question. This model holds CARB Zero Ozone certification, under 5 parts per billion.

That deserves saying plainly, because the larger 311i Max has no such certification and gives you no way to switch its charge off.

It is cheaper to feed than the model above it

Those are the numbers — see what it costs today.

Two drawbacks worth knowing

The room size in the title is not the room size to buy for

That 1,138 sq ft assumes one air change an hour. Blueair recommends 237 sq ft, at 4.8 changes.

One change an hour achieves very little in hay fever season. Measure the room and work from the smaller number.

The naming compounds it. The 311i Max is rated for 439 sq ft, and the two models differ by a single digit.

The carbon layer is thin, and replacing it wastes good HEPA

Particles and odour share one combined filter, and the carbon portion of it is slim.

Cooking, pets and VOCs will get through. Blueair's answer is a higher-carbon filter at a US price of $77.98 for two.

Change it for odour and you throw away a particle layer with months left. That is the cost of the one-piece design.

Who this suits

A good fit if you

• Are treating one bedroom or a study up to about 22 m²
• Sleep next to the unit and put silence above raw airflow
• Intend to run it permanently and want the lowest standing cost

Look elsewhere if you

• Need one machine to handle an open-plan sitting room
• Are mainly trying to shift cooking smells or chemical odours

Still on your shortlist? See today's price.

What to pay

The US list price is $139.99, roughly £110 at current rates, though UK street prices move independently. The sticker is the smaller half of what you will spend.

Genuine filters are $59.98 for two on US list, about $30 each, with pre-filters at $8.99. The unit stretches a filter to nine months before it asks for a change.

Replace twice a year and you are looking at around £50 of filters plus £40 of electricity. That total, not the shelf price, is what to compare.

Check today's price on AmazonBlueair Blue Pure 511i Max →

Questions people ask before buying

How big a room will the Blue Pure 511i Max really cover?

237 sq ft, about 22 m², at 4.8 air changes an hour. The 1,138 sq ft figure assumes one change an hour and is no use for allergies.

CADR is the number that decides whether a purifier can keep up with your room explains why the two figures differ so widely.

Does it give off ozone?

No measurable amount. It carries CARB Zero Ozone certification, below 5 parts per billion.

That is a real difference from the 311i Max, whose electrostatic stage cannot be turned off and holds no such certification.

What will it add to the electricity bill?

Roughly 149 kWh a year at 17 watts running continuously, a little over £40 at a typical unit rate. Auto mode brings that down by dropping the fan once the air is clean.

As an Amazon Associate I earn from qualifying purchases. This post contains affiliate links. We were not given this product and were not paid to write about it.