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The evidence

Proof, not promises.

What is in your air, what our filters capture, how we measure room sizes, and what a purifier cannot do for you.

  • H13 + carbonThree filtering layers in every purifier
  • 371 CFMCADR, Klarta Stor
  • 20 dB(A)Sleep mode, Klarta Forste
  • 1 yrMinimum filter change, both purifiers

01 · What it removes

What it takes out of the air.

A human hair is about 70 microns across, roughly a thousandth of an inch. Everything below is smaller than that, which is why it stays in the air you breathe at home.

  • Smog & PM2.5 ≤2.5 µm Caught by H13 filter

    Traffic, heating and smoke particles small enough to stay airborne for hours. The H13 filter helps capture fine particles as small as 0.003 microns.

  • Plant allergens 10–100 µm Caught by pre-filter + H13

    Grass, tree and shrub pollen carried in through windows and on clothing. The pre-filter stops the larger grains and the H13 filter helps capture the rest.

  • Pet dander & mites 10–40 µm Caught by pre-filter + H13

    Allergens from pets, bedding and dust mites, stirred up every time you move. The pre-filter and H13 filter help capture them as the air passes through.

  • Mold & fungal spores 2–10 µm Caught by H13 filter

    From bathrooms and damp walls, spores stay airborne long after the damp has dried. The H13 filter helps capture them.

  • Gases & odors molecular Caught by activated carbon

    Formaldehyde and other VOCs, cigarette smoke and cooking smells: the gases and odors a particle filter cannot hold, absorbed by the activated carbon filter.

A white Klarta air purifier standing beside a side table, its round display reading 72°F, 50% humidity and a PM2.5 level of 10 in Turbo mode.

02 · How we stop it

Three layers, in this order.

Each layer protects the next, which is why the sequence matters as much as the materials. Skip the pre-filter and you lose months of filter life.

  1. 01

    Pre-filter

    Catches hair, lint and larger dust. Vacuum it on low with a soft brush every two weeks, more often with pets.

  2. 02

    H13 particle filter

    Helps capture fine particles as small as 0.003 microns, including smoke particles, mold spores, and plant, animal and dust-mite allergens.

  3. 03

    Activated carbon

    Absorbs gases such as formaldehyde and other VOCs, and helps reduce cigarette-smoke and cooking odors.

04 · The wider research

Published sources, linked in full.

Every claim below is someone else's published work — peer-reviewed research or public guidance, never ours. Click through and read it.

  1. 01 WHO · 2021

    The bar for clean air moved, and it moved down.

    After a systematic review of fifteen years of evidence, WHO halved its annual PM2.5 guideline from 10 to 5 µg/m³ — set at the lowest exposure with clear evidence of adverse health effects.

    WHO Global Air Quality Guidelines, 2021 opens in a new tab

  2. 02 IQAir · world report

    Almost nowhere meets that guideline.

    In the first global report measured against the new value, 222 of 6,475 cities met the annual PM2.5 guideline — about 3%. Not one country did.

    IQAir 2021 World Air Quality Report opens in a new tab

  3. 03 Int. J. Hygiene & Env. Health

    40–60% humidity is the range to hold.

    A peer-reviewed review calls 40–60% relative humidity the range for optimal airway function, and links dry air below it to more acute eye and airway symptoms.

    Wolkoff, Int J Hyg Environ Health 256, 2024 opens in a new tab

  4. 04 AHAM · US standard

    CADR is the number worth comparing.

    The ANSI/AHAM AC-1 method scores portable air cleaners separately for tobacco smoke, dust and pollen — a like-for-like figure no marketing room size can substitute for. Klarta publishes one PM2.5 CADR per model: 165 CFM on Forste, 371 CFM on Stor.

    AHAM Verifide air filtration standards opens in a new tab

  5. 05 US EPA

    Filtration is a supplement, not a substitute.

    EPA puts source control and ventilation first, and says research shows filtration can be an effective supplement to both. EPA neither certifies nor recommends particular brands, including ours.

    EPA Guide to Air Cleaners in the Home opens in a new tab

05 · How we measure

Where our room sizes come from.

  • CADR

    165 / 371 CFM

    Clean Air Delivery Rate — filtered air delivered per minute. Forste: 165 CFM. Stor: 371 CFM.

  • ACH

    1 → 3

    Air changes per hour. Our headline room sizes assume 1 ACH; in a room a third of that size the same unit reaches 3 ACH.

  • Why size down

    A purifier sized above your room reaches clean air on a lower fan speed, so it runs quieter more of the time.

  • Noise & power

    20 / 24 dB

    Sleep mode runs at 20 dB(A) on the Klarta Forste and 24 dB(A) on the Klarta Stor, drawing about 5–7 W.

  • Auto modes

    Auto Turbo, Auto Normal and Auto Sleep use the laser PM2.5 reading to pick the fan speed, across 8 speeds on the Klarta Forste and 6 on the Klarta Stor.

  • Filter life

    The US manuals recommend replacing the particle and carbon filters at least once a year. The display tells you, based on how the device actually ran.

06 · Honestly

What a purifier will not do.

We would rather you buy the right thing than the most expensive thing.

  • It is not a medical device. It helps capture airborne particles; it does not treat allergies or asthma.
  • It does not replace ventilation. Filtration removes particles; fresh air removes CO₂.
  • It does not fix damp or mold at the source — find the leak first.
  • It works in the room it stands in. Air does not travel freely between closed rooms.

Still deciding?

Tell us your room size and we will tell you honestly whether you need one unit or two.

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