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April 12, 2026

How to Choose an Air Purifier (2026 Buyer's Guide)

Most air purifier marketing is noise. Here's what actually matters when picking one - based on CADR data, EPA testing, and what works for PM2.5.

Step 1: HEPA. Non-negotiable.

A "True HEPA" filter captures 99.97% of particles ≥0.3 μm. Anything labeled "HEPA-type", "HEPA-style", or just "HEPA" without "True" is marketing fluff.

Skip:

  • Ionic / ozone purifiers (produce ozone, a lung irritant)
  • "PCO" (photocatalytic oxidation) - poorly evidenced
  • UV-only - kills microbes but doesn't capture PM2.5

Step 2: CADR rating > marketing claims

CADR (Clean Air Delivery Rate) measures m³ or CFM of clean air delivered per unit time. AHAM-certified CADR is the only number to trust.

Rule of thumb: pick a CADR (in CFM) ≥ 2/3 of your room's square footage. So a 300 sq ft bedroom needs CADR ≥ 200.

For aggressive filtration (5 air changes per hour, recommended during wildfire smoke), you want CADR closer to your room area in CFM.

Step 3: Room sizing math

Volume of room (cubic feet) ÷ CADR (cubic feet per minute) = minutes per air change.

Target: 3-5 air changes per hour = clean air every 12-20 minutes.

| Room | Recommended CADR (smoke) | |------|--------------------------| | Small bedroom (150 sq ft) | 100+ | | Standard bedroom (250 sq ft) | 165+ | | Living room (400 sq ft) | 270+ | | Open plan (700 sq ft) | 470+ |

Step 4: 5 features that actually matter

  1. CADR rating matched to room size (above)
  2. Carbon filter for VOCs and odors (cooking, traffic, wildfire smoke chemicals)
  3. Quiet mode under 35 dB - if it's loud, you'll turn it off and waste money
  4. Filter replacement cost - real cost is filters, not the unit. Some run $200/year.
  5. PM2.5 sensor built in for auto mode. Lets it ramp up only when needed.

Skip these features

  • WiFi/app control - cute but adds failure modes
  • "Smart" features beyond auto-sensing - mostly marketing
  • "Plasma" / "ionizer" modes - turn them off, they produce ozone
  • Decorative "wood grain" finish - irrelevant

DIY alternative: Corsi-Rosenthal Box

A 20" box fan + 4 MERV-13 filters taped into a cube delivers CADR equivalent to a $500 purifier for ~$80. Tested by Berkeley Lab. Loud but effective. Search "Corsi-Rosenthal box" for build guides.

Maintenance

  • Replace HEPA filters every 6-12 months (more often if AQI is high)
  • Replace pre-filters every 3 months
  • Clean external grille monthly

Bottom line

Pick a True HEPA unit with AHAM-certified CADR matched to your room size, with a carbon stage and quiet mode. Skip everything else. Track your city's PM2.5 to know when to run it on high: live AQI here.

This guide is independent and not affiliate-driven. Last reviewed: 2026-05-02.