Home & Lifestyle buying guide

How to choose an air purifier

A portable air purifier removes particles such as dust, smoke and pollen from one room. The two things that matter most are a true HEPA-type filter and enough clean air delivery rate (CADR) for your room size. Purifiers do not replace ventilation or fixing the source of pollution.

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Weighted criteria

What matters when choosing air purifiers

Weights add up to 100 and reflect how much each factor usually decides satisfaction. Change them to fit you in the scorecard.

  1. CADR for your room size

    30%

    Clean air delivery rate: how much filtered air the unit supplies. Higher CADR cleans a given room faster.

    How to check: Measure the room area and compare it with the maker's recommended room size; prefer a tested CADR figure over a vague "covers up to" claim.

  2. Filter type

    25%

    A true HEPA or HEPA-grade filter captures fine particles; activated carbon helps with some odours and gases.

    How to check: Look for a named filter grade, not just "HEPA-like" or "HEPA-type". Check carbon weight if odours matter to you.

  3. Filter & running costs

    15%

    Replacement filter price and interval, plus electricity use when running all day.

    How to check: Find the replacement filter price and life before buying; check power draw on the spec sheet.

  4. Noise at useful speeds

    15%

    How loud it is on the setting you will actually use, not just on its quietest mode.

    How to check: Read the decibel figure for each fan speed; for bedrooms, test the speed that reaches your room's needed CADR.

  5. No ozone emission

    15%

    Ionisers and "ozone generators" can emit ozone, which irritates the lungs.

    How to check: Avoid ozone generators; if the unit has an ioniser, check that it can be switched off and that it is certified for low ozone emission where such certification exists (for example in California).

Avoid

Red flags

  • Claims that it kills viruses or prevents illness without independent test data.
  • "HEPA-type" or "HEPA-like" filters with no stated grade.
  • Devices sold as ozone generators for occupied rooms.
  • No replacement filter available to buy separately.
  • A room-size claim with no CADR behind it.

Before you pay

Checklist

  1. Measure the room you want to clean.
  2. Shortlist units whose CADR fits that room.
  3. Check filter grade and replacement cost.
  4. Check noise at the speed you will use.
  5. Make sure it does not emit ozone.
  6. Keep doors and windows managed and fix pollution sources where you can.

Ask the seller

Questions to ask

  • What is the tested CADR, and who tested it?
  • What does a replacement filter cost, and how long does it last?
  • Does it have an ioniser, and can I turn it off?

After you buy

Warranty & returns

Purifiers commonly carry a one or two year warranty on the unit; filters are consumables and are not covered.

  • Register the product so you are told about recalls.
  • Using non-approved filters may affect warranty cover.

Track the return window and warranty end date

Common mistakes

Myths vs facts

Myth An air purifier cleans the whole house.

Fact Portable units clean one room at a time. Whole-home filtration needs a ducted system.

Myth More features means cleaner air.

Fact CADR and filter grade drive results. Apps and sensors are convenient but do not clean air by themselves.

Where this comes from

Official sources

Criteria and weights are AltFTool's editorial judgement, not a statement by these bodies. This guide is general consumer information, not professional advice.

FAQ

Air Purifiers: common questions

Do I need an air purifier?

It can help if you live with smoke, heavy outdoor pollution, pet dander or pollen. Reducing sources and ventilating well come first.

How often should I change the filter?

Follow the maker's interval, and change it sooner in very polluted conditions. A clogged filter lowers CADR.

Can I run it all day?

Yes, most are designed for continuous use. Check the power draw so you know the running cost.

Free tools

Use these with this guide

Weighted scorecard

Review pattern checker

Complaint letter writer

Warranty & returns tracker

True cost calculator

Also handy: home air filter reminder, aqi today

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