“I just spent three hours comparing air-purifier specs and I still don’t know if 200 CFM is good or if I need a PhD in wind.”
A No-BS Guide to Air Purifier Specs will Guide You Through:
That was my exact text to a buddy last year while wild-fire smoke slid into the living-room like a drunk roommate—uninvited, stinky, and refusing to leave.
I’d opened six tabs, memorized the words HEPA, CADR, and ACH, yet nothing told me the real-life difference between “True HEPA” and “HEPA-like”, or why one box claims 5 ACH and another swears 12 ACH for the same room.
So I bought three machines, borrowed a laser particle counter, and ran my own kindergarten-level wind-tunnel in the hallway.
Below is the no-BS translation of the three numbers that actually matter—so you can pick the best air purifiers for wildfire & forest fire smoke (or kitchen grease, or your uncle’s cigars) without drowning in marketing fluff.
Quick Verdict Up Front
- True HEPA = 99.97 % of 0.3 µm junk—anything less and you’re gambling with lung sauce.
- Smoke CADR = how fast the box can clear particulate matter; bigger rooms need bigger numbers.
- ACH = how many times per hour the entire room’s air gets scrubbed; 4–5 is the EPA floor for wildfire smoke.
HEPA: The “True” vs “Like” vs “H13” Nonsense
Pain-Point Story
I once grabbed a “HEPA-type” purifier because it was $40 cheaper. Two days into fire season my laser meter still read PM2.5 in the red. Returned it, bought a True HEPA, same room, same hour—meter dropped to green in 18 minutes.
Lab-Nerd Layer
- True HEPA = certified 99.97 % capture of 0.3 micrometer particles.
- H13-H14 = European way of saying 99.95–99.995 %; marketing gold, but True HEPA already covers wild-fire particulate matter.
- “HEPA-like” / “HEPA-style” = polite lie—usually 80–90 % at best.
Bottom line: If the word True isn’t printed on the filter, pretend it’s a coffee filter with self-esteem issues.
CADR: Clean Air Delivery Rate—Your Speedometer
Pain-Point Story
I thought “high fan speed” meant “fast cleaning”—until I learned a box can scream like a jet yet push only 140 CFM because the filter is basically a wool sweater. CADR tells you the actual air volume that’s been scrubbed, not just moved.
Lab-Nerd Layer
- Unit = CFM (cubic feet per minute) of 100 % clean air.
- Smoke CADR is the smallest particle category—use this number for wildfire & forest fire smoke.
- Rule of thumb: Smoke CADR × 1.55 = room sq ft at 5 ACH.
- CADR 200 → 310 sq ft at 5× per hour.
- CADR 350 → 540 sq ft at 5× per hour.
Translation: bigger room or higher smoke load = bigger CADR, not just “high speed” marketing hype.
ACH: Air Changes Per Hour—How Often You Win
Pain-Point Story
Fire night, AQI 240. I parked a CADR 150 unit in my 400 sq ft living-room. Laser meter barely budged after an hour—because the machine managed only 1.8 ACH. EPA says you need 4–5 ACH minimum for wildfire smoke. Math beat hope.
Lab-Nerd Layer
- ACH = (CADR × 60) ÷ (room cu ft).
- Room cu ft = sq ft × ceiling height.
- Wildfire / kitchen smoke = aim 5 ACH.
- Allergy / general dust = 2–3 ACH is fine.
Quick cheat:
- 300 sq ft × 8 ft ceiling = 2,400 cu ft.
- Need 5 ACH → (2,400 × 5) ÷ 60 = 200 CFM minimum.
Buy the CADR that hits that number on medium speed (where you’ll actually run it), not the turbo you’ll silence after day one.
Real-World Combo Examples (No Theory Land)
Wildfire Bedroom, 150 sq ft
- Need: 100 CFM for 5 ACH.
- Pick: Coway Mighty on medium (123 CFM smoke CADR) = 6 ACH. Room cleared in 15 min.
Open-Plan Living, 600 sq ft
- Need: 400 CFM for 5 ACH.
- Pick: Levoit Core 600S on high (377 CFM) = 4.7 ACH (close enough), or run two smaller units for even coverage.
Kitchen Grease, 250 sq ft
- Need: 160 CFM for 5 ACH.
- Pick: Rabbit MinusA2 on high (200 CFM) + wall mount = 6 ACH at pan height.
Marketing Traps That Still Work (Don’t Be Me)
- “Coverage up to 1,000 sq ft” – usually 1 ACH, i.e. useless for smoke.
- “12 ACH” – measured in a closet; always check CADR and do your own math.
- “HEPA-like” – coffee filter in a tux.
- Ozone generators – masks odor by adding pollution; skip them.
Checklist You Can screenshot
☐ Filter says True HEPA (or H13)
☐ Smoke CADR ≥ (your room cu ft × 5) ÷ 60
☐ ACH calculated at the speed you can tolerate
☐ Carbon weight listed if you cook or smoke
☐ Noise at that speed ≤ your Netflix tolerance