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Portable Air Cleaners: How to Size One and What Specs to Trust

Researched guide · last reviewed November 8, 2026

Researched from public sources, not a hands-on review. Not medical advice.

EPA’s guide to air cleaners in the home says the most effective ways to improve indoor air are to reduce or remove pollutant sources and to ventilate with clean outdoor air. Filtration can supplement that. A portable air cleaner can reduce indoor air pollution. It cannot remove all of it.

Key criteria

  1. CADR (clean air delivery rate). EPA says to choose a CADR large enough for the room. A higher CADR moves more particles and can serve a larger area. Packaging usually states the largest room the unit should serve. CADR on the box is typically measured at the unit’s highest speed, so the number is not the rate you get on a quiet setting.
  2. Smoke, dust, and pollen are three CADR numbers, not one. EPA says some packages list CADR for tobacco smoke, dust, and pollen, standing in for small, medium, and large particles. For the small particles, EPA says to look at a high CADR for tobacco smoke. The same EPA page shows an AHAM label beside that explanation. It does not, in the text we could read, define the AHAM Verifide program’s test method, so this guide does not restate that method.
  3. A sizing chart, for an 8-foot ceiling. EPA publishes this as an estimate, not as a rule for every room. Higher ceilings call for a higher CADR.
Room area Minimum CADR
100 sq ft 65 cfm
200 sq ft 130 cfm
300 sq ft 195 cfm
400 sq ft 260 cfm
500 sq ft 325 cfm
600 sq ft 390 cfm

EPA’s published chart stops at 600 square feet. This guide does not extend it.

  1. Filter type. EPA says portable cleaners often reach a high CADR with a HEPA filter, meaning a high-efficiency particulate air filter. “HEPA-type” and “HEPA-like” are not that term. We did not find a single consumer-product definition of “true HEPA” on the EPA page, so CADR is the number to compare. For gases and some odors, EPA says to look for activated carbon or another gas filter, and that there is no widely used rating system for gas removal. Carbon filters need a large amount of material. Washable “permanent” filters are a different product; do not assume they are HEPA.
  2. Ozone. EPA says to avoid portable air cleaners and furnace filters that intentionally produce ozone. Ozone is a lung irritant. Some units with electrostatic precipitators, ionizers, ultraviolet lamps without adequate coatings, or plasma may also emit ozone. EPA points to lists kept by the California Air Resources Board and by AHAM of air cleaners tested to emit little or no ozone. Prefer a model on one of those lists rather than a marketing line about “certified air.”
  3. Running cost, without a price in this guide. Check the replacement-filter interval and the power draw yourself. ENERGY STAR certifies efficient room air cleaners. Filter prices change and are not quoted here.
  4. Noise at the speed you will use. The CADR you shopped for may be the high-speed number. If you will run the unit overnight on low, look for a decibel figure at that speed. A larger unit run on a lower speed can be quieter than a small unit run flat out. That is a tradeoff, not a measurement we made.

Tradeoffs

Alternatives and complements

Sources