EPA Sizing Guide

EPA Wildfire Smoke Air Cleaner Guide: The 2/3 CADR Rule

Use the EPA baseline, understand AHAM's stronger wildfire target, and turn room area into a defensible smoke-CADR specification.

By the LYL Clean Air Engineering Team · Published Jul 12, 2026 · Updated Aug 9, 2026

Quick answer For a room with an 8 ft ceiling, the EPA baseline is tobacco-smoke CADR (CFM) ≥ two-thirds of room area (ft²). A 120 ft² room therefore needs at least 80 CFM. During wildfire smoke, AHAM recommends the more conservative target of smoke CADR roughly equal to room area — 120 CFM in that example. Size up for higher ceilings, run the cleaner continuously on high, and use a separate substantial activated-carbon stage if odor control matters.

Chart: wildfire smoke rooms need high CADR - roughly 520 cubic metres per hour for a 40 square metre space at 5 air changes per hour — EPA's 2/3 rule is a baseline for an 8 ft ceiling; AHAM recommends a higher smoke-CADR target during wildfire events.

Wildfire smoke is the one scenario where much of the everyday air-purifier advice inverts: quiet modes, auto modes and ordinary sizing all give way to continuous clean-air output. The baseline below comes from current US EPA wildfire guidance; the higher target comes from AHAM's wildfire-specific recommendation.

EPA 2/3 CADR rule: worked room-size examples

Baseline formula: minimum tobacco-smoke CADR (CFM) = room area (ft²) × 2/3, assuming an 8 ft ceiling. AHAM recommends matching smoke CADR to the room's square footage for stronger wildfire performance.

Room area	EPA 2/3 baseline	AHAM wildfire target
120 ft²	80 CFM	120 CFM
300 ft²	200 CFM	300 CFM
600 ft²	400 CFM	600 CFM or multiple units

Ceiling rule: both figures assume an 8 ft ceiling. For a higher ceiling, use a larger cleaner or calculate by room volume and target air changes with the CADR calculator.

The EPA clean-room playbook, step by step

Step	What to do	Why
1. Pick one room	A bedroom or living room the household can stay in; doors and windows closed	Concentrate clean-air capacity where people actually are
2. Stop making particles	No cooking, candles, smoking or vacuuming in the clean room	Indoor sources can rival the smoke you're keeping out
3. Run HEPA on high, continuously	Highest fan speed for the duration of the event	EPA smoke guidance — infiltration outpaces low settings
4. Size by smoke CADR	EPA baseline: tobacco-smoke CADR (CFM) ≥ 2/3 of room area (ft²)	Use AHAM's room-area target for heavier wildfire smoke
5. Watch the outdoor AQI	Track AirNow.gov; air out the house when outdoor air clears	Smoke events pulse — ventilate in the clean windows

Sources: US EPA — preparing for smoke and heat; US EPA — create a clean room; AHAM Verifide — air filtration standards.

The part HEPA cannot do: the smell

Smoke is particles plus gases. HEPA media captures the PM2.5 that damages lungs, but the campfire smell rides on gases and VOCs that sail through any particle filter. Two consequences:

Odor control needs real activated carbon — substantial mass, not a spray-coated pad. The same rule as VOC removal: performance is proportional to carbon quantity and contact area.
Carbon saturates fast in heavy smoke. A filter that lasts a year in normal use can exhaust its carbon in weeks of continuous smoke duty. Households should stock a spare filter set before the season — and retailers should plan inventory the same way.

Why the "run it on high" advice inverts normal guidance

Our noise guide tells bedroom buyers to size up so the quiet setting suffices. Smoke events flip that: the priority is maximum clean-air output, and EPA guidance says to run the cleaner continuously on its highest fan setting. If noise is a concern, choose a larger unit whose lower setting still meets the required tested smoke CADR. Use the CADR calculator at 5–6 air changes per hour for a smoke-ready target.

What this means for brands and distributors

Smoke season is a demand pulse, not a trend — North American and Australian fire seasons reliably spike search and retail demand. Inventory and content should be in place a quarter ahead.
Spec the smoke CADR, not just "coverage." Buyers following EPA/AirNow guidance look for the smoke figure specifically; we quote it from the SKU's AHAM AC-1 or GB/T 18801 test report.
Bundle replacement filters. A machine + spare-filter bundle matches how smoke actually consumes carbon, raises order value, and prevents the "filter sold out mid-event" review.
High-CADR towers and commercial units are the right platforms for this positioning — see tower OEM and commercial OEM.

Stocking for smoke season?

Tell us your market and room-size targets — we will match high-CADR HEPA + carbon models, quote smoke CADR from test reports, and plan machine + filter bundles.

Request Model Options

Frequently asked questions

Do air purifiers work for wildfire smoke?

Yes — EPA advises using a properly sized HEPA portable air cleaner to reduce indoor smoke particles. Size by tobacco-smoke CADR, run it continuously on high and keep the clean room closed.

What CADR is needed for a 120 ft² room?

The EPA 2/3 baseline is at least 80 CFM for an 8 ft ceiling. AHAM's stronger wildfire target is about 120 CFM. Size up for higher ceilings or heavy smoke.

Does HEPA remove the smoke smell?

No. The smell is gases/VOCs that pass through HEPA; you need a substantial activated-carbon stage, and it saturates faster during smoke events.

High or quiet mode during a smoke event?

High, per EPA guidance — or size up so medium speed already meets the target. Everyday quiet-mode advice applies to everyday air.

Related guides

CADR calculator — set it to 5–6 ACH for smoke-ready sizing.
Smoking-room configuration — the heavy-carbon architecture smoke demands.
Corsi-Rosenthal box vs commercial — the DIY option many households use in emergencies.
Granular carbon vs carbon cloth — why carbon mass decides odor performance.

General guidance based on cited public-health sources; not medical advice. For health decisions during smoke events follow local authorities. Confirm smoke CADR against the SKU test report.

Buyer FAQ

Frequently Asked Questions

Do air purifiers work for wildfire smoke?

Yes. The US EPA advises using a properly sized portable air cleaner with a HEPA filter to reduce wildfire-smoke particles indoors. For an 8-foot ceiling, EPA guidance uses a tobacco-smoke CADR of at least two-thirds of the room's area in square feet, with continuous operation on the highest fan setting during smoke events.

What CADR is needed for a 120 square foot room during wildfire smoke?

EPA's two-thirds baseline gives a minimum tobacco-smoke CADR of 80 CFM for a 120 square foot room with an 8-foot ceiling. AHAM recommends a stronger wildfire target: smoke CADR equal to the room area, or about 120 CFM in this example. Size up for ceilings above 8 feet or very heavy smoke.

What is a clean room during a wildfire?

An EPA-recommended strategy: pick one room the household can stay in, keep its doors and windows closed, avoid particle-generating activities like cooking or candles, and run a properly sized HEPA air cleaner continuously. The goal is to keep at least one room's air markedly cleaner than the rest of the home during a smoke event.

Does HEPA remove the smoke smell?

Not by itself. HEPA captures smoke particles, but the smell comes largely from gases and VOCs, which pass through HEPA media. Removing the odor requires a substantial activated-carbon stage, and the carbon saturates faster during heavy smoke, so plan replacement filters accordingly.

Should the purifier run on high or quiet mode during smoke events?

On high. EPA guidance for smoke events is to run the air cleaner continuously at its highest fan speed. If noise is a concern, choose a larger unit whose lower setting still delivers the required tested smoke CADR.