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Environment

Air filters — HEPA, VOCs, and wildfire smoke

Applies to: Lung, general

Air filters — HEPA, VOCs, and wildfire smoke

Indoor air can be more polluted than outdoor air. A good HEPA purifier won't fix everything, but it can meaningfully reduce fine particles, smoke, and some VOC exposure.

This is educational information, not medical advice. Always talk to your care team about what applies to your specific situation.

Full guide

The bottom line

Indoor air can be more polluted than outdoor air, and some of that pollution matters for lung health and cancer risk — fine particulate matter (PM2.5), radon (covered separately), volatile organic compounds (VOCs) from furniture and cleaning products, and wildfire smoke. A good air purifier won’t fix everything, but for particulates and smoke, it genuinely helps.

What a HEPA filter does and doesn’t do

A true HEPA filter captures 99.97% of particles down to 0.3 microns. That includes the fine particulate matter (PM2.5) in wildfire smoke and general air pollution, which is the stuff most linked to lung damage and cancer risk. What HEPA does NOT do: remove gases, VOCs, or odors. For those you need an activated carbon filter (often included alongside HEPA in better units).

Matching the filter to the concern

  • Wildfire smoke / general particulates: a true HEPA purifier sized to your room. This is the single most useful air-quality upgrade for most people.
  • VOCs / off-gassing / odors: look for a unit with a substantial activated carbon filter, not just HEPA.
  • Both (most people): a combination HEPA + carbon unit.
  • Whole-home: upgrade your HVAC filter to a MERV 13 rating if your system supports it. It filters as air circulates.

Sizing matters more than brand

The key spec is CADR (Clean Air Delivery Rate). It should match your room size. An undersized purifier in a big room does little. Look for the AHAM Verifide seal and a CADR rated for your square footage. A rough rule: the CADR (in cfm) should be at least two-thirds of your room’s area in square feet.

The free and cheap options

You don’t always need an expensive unit. During wildfire smoke events, a DIY box-fan filter (a "Corsi-Rosenthal box"). A box fan taped to MERV 13 furnace filters — performs remarkably well for under $50. The EPA and air-quality researchers endorse it as an emergency measure.

Resources

  • EPA Guide to Air Cleaners in the Home: epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home.
  • AirNow: airnow.gov — real-time local air quality index.
  • AHAM Verifide: ahamverifide.org — verify CADR ratings.
  • Corsi-Rosenthal box instructions — widely available; a cheap DIY option for smoke season.
  • Brands with true-HEPA + carbon units: Coway, Levoit, Blueair, Austin Air (varies by need and room size).

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