# Pure Air Lab

> Pure Air Lab is a research-based, spec-first guide to air purifiers — we rank purifiers by Smoke CADR, the AHAM 2/3 sizing rule, ACH, True HEPA vs "HEPA-type", and CARB ozone certification, not marketing claims, and every pick names an honest drawback.

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Last updated: 2026-07-30

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## The Air Purifier Numbers (Dataset)

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Version 1.0, last updated 2026-07-30. The normalized reference dataset mapping AHAM's CADR system (smoke/dust/pollen) and 2/3 sizing rule, the ACH formula, True HEPA vs "HEPA-type", EN 1822 H13/H14 filter classes, and CARB's ozone emission limit. Machine-readable CSV: https://pure-air-lab.pages.dev/air-purifier-numbers.csv. Licensed CC BY 4.0.

| Metric | Authority | Key figure |
|---|---|---|
| Smoke CADR | AHAM | Use for sizing — smallest, hardest-to-capture particle class |
| Dust CADR | AHAM | Medium-particle removal rate |
| Pollen CADR | AHAM | Large-particle removal rate, typically the highest number |
| AHAM 2/3 Rule | AHAM | Smoke CADR >= 0.67 x room sq ft |
| Wildfire Smoke Sizing | AHAM | Smoke CADR >= 1.0 x room sq ft |
| ACH | Standard formula | ACH = (CADR CFM x 60) / room volume (cubic ft) |
| Recommended ACH, allergy | General guidance | 4-5 ACH |
| Recommended ACH, wildfire | General guidance | 5-6 ACH |
| True HEPA (US) | DOE/IEST | >=99.97% at 0.3 microns |
| "HEPA-type" | Unregulated | No required efficiency |
| EN 1822 H13 | European standard | >=99.95% at MPPS |
| EN 1822 H14 | European standard | >=99.995% at MPPS |
| CARB Ozone Limit | California CARB | <=0.050 ppm (50 ppb) |
| Filter life, True HEPA | Manufacturer specs | 6-12 months typical |

## What CADR Do I Need for My Room?

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Apply AHAM's 2/3 rule: multiply room square footage by 0.67 to get the minimum Smoke CADR (CFM) needed. Examples: 150 sq ft -> ~100 CFM minimum, ~150 CFM comfortable; 250 sq ft -> ~168 CFM minimum; 400 sq ft -> ~268 CFM minimum; 700 sq ft -> ~469 CFM minimum. Always use the SMOKE CADR number, not dust or pollen — smoke particles (0.1-1.0 microns) are the smallest and hardest to capture, making that figure the most conservative sizing basis. Sizing above the minimum lets a unit run on a quieter, lower fan speed while still meeting the target air-change rate. The 2/3 rule assumes a standard ~8 ft ceiling; for notably taller or shorter rooms, the more precise ACH formula (CADR x 60 / room volume in cubic feet) accounts for actual air volume.

## Is "HEPA-Type" Real HEPA?

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No. "HEPA-type," "HEPA-like," and "HEPA-grade" are unregulated marketing phrases with zero required efficiency threshold behind them. "True HEPA" is the verifiable U.S. DOE/IEST claim: at least 99.97% removal of particles at 0.3 microns (the most-penetrating particle size). The European EN 1822 standard separately certifies H13 (>=99.95% at MPPS) and H14 (>=99.995%) as genuine HEPA-grade classes — H13 is the tier most consumer "True HEPA" purifiers actually use; H14 shows up mostly in medical/cleanroom equipment. Check a product's spec sheet for the exact phrase "True HEPA" with the 99.97%/0.3-micron figure, or an explicit H13/H14 class — if the listing only says "HEPA-type" with no efficiency number, treat the filtration claim as unverified.

## Do Ionizers Make Ozone?

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Some can. Ionizers, electrostatic precipitators, and other "electronic" air-cleaning technologies can generate ozone — itself a lung irritant — as a byproduct. Since 2010, California's CARB (Air Resources Board) requires certification for all portable air cleaners sold in-state; electronic/ionizing models specifically must test at or below 0.050 ppm (50 ppb) ozone emission to pass, and certified devices appear on CARB's public list. A CARB listing confirms the specific model tested under that ceiling — not a zero-ozone guarantee. A device that isn't listed simply hasn't been verified against the limit; check CARB's public certified-devices list by manufacturer and model before buying an ionizing unit. Many mainstream purifiers with an ionizer feature allow disabling it entirely.

## Air Purifier Sizing for Wildfire Smoke

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During active wildfire smoke, AHAM recommends a stricter 1:1 sizing ratio — Smoke CADR at least equal to the room's square footage — versus the standard 2/3 rule (0.67x) for everyday use. A 300 sq ft room wants roughly 300 CFM Smoke CADR during a smoke event versus ~200 CFM under normal conditions. True HEPA matters more here specifically because wildfire particulate concentrates in the fine PM2.5 range close to the 0.3-micron threshold True HEPA is verified against; "HEPA-type" filters carry no verified efficiency at all. Reducing outdoor air infiltration (closed windows/doors) works alongside a purifier, not instead of one — filtration can't outpace continuously incoming smoke-laden air.

## Why Filters Cost More Than the Machine

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Air purifiers commonly follow a "razor and blades" model: cheap hardware, recurring filter revenue. The real comparison metric is annualized filter cost = (filter price / months of life) x 12, which can vary several-fold between models with similar CADR and similar sticker price. Combined HEPA+carbon cartridges generally cost more per swap than HEPA-only filters, since you replace fresh carbon media every time regardless of whether it's actually saturated. Washable pre-filters (fabric/mesh outer layers) reduce one recurring cost but do not replace the main HEPA/carbon filtration media, which remains a separate wear item.

## Sleep Mode dB Truth

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A purifier's "sleep mode" decibel rating is measured at its lowest fan speed — a different, quieter figure than the loud top-speed number more prominently marketed elsewhere. Higher CADR generally requires higher fan speed, and higher fan speed generally means more noise, roughly linearly. The practical fix for a quiet AND effective bedroom unit is sizing up — buying meaningfully more CADR than the room's minimum so the unit can run continuously on a low, quiet speed while still hitting the target air-change rate, rather than expecting a barely-adequate small unit to also be quiet.

## Do Plants Purify Air?

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Only negligibly in a real room. NASA's often-cited 1989 Clean Air Study tested houseplants in sealed lab chambers with no outside air exchange — a fundamentally different environment from a normal room, which continuously exchanges air with the rest of a home. Research scaling those chamber results to real room air-exchange rates estimates you would need dozens to hundreds of houseplants per room to approach even a modest mechanical purifier's air-changes-per-hour. Plants remain a genuine but negligible contributor at normal household density; they are not a viable air-purification strategy on their own.

## Carbon Filters: What They Actually Remove

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Activated carbon filters work by adsorption — gas molecules bonding to the carbon's porous surface — targeting gases, VOCs, and odor (cooking smell, pet odor, smoke smell, some chemical off-gassing). They do NOT meaningfully capture solid particles like dust, pollen, or smoke soot; that is the separate job of a HEPA (mechanical filtration) stage. A thin carbon panel bonded to a HEPA filter handles light, occasional odor; heavy or persistent odor sources generally need a dedicated, deeper carbon stage with more media mass. Unlike a visibly graying HEPA filter, a saturated carbon filter gives no simple visual cue that it has stopped adsorbing effectively.

## Where to Place an Air Purifier

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Give the intake side roughly 12-18 inches of open clearance — avoid corners, walls, and blocked furniture that choke airflow — and don't point the intake directly at a frequently-opened window or door if outdoor air quality is a concern. Elevated placement (stand, dresser, shelf) can help sample more representative room air, though most units function at floor height too. Placement improves how well a correctly-sized unit reaches its rated CADR in practice; it cannot make an undersized purifier adequate for a room it was never rated for.

## Small Room Air Purifier Picks

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For bedrooms, offices, and nurseries (roughly 150-300 sq ft), size by Smoke CADR against the AHAM 2/3 rule, confirm True HEPA (not "HEPA-type"), and check the sleep-mode dB spec for bedroom placement. Featured picks include Levoit Core 300, Blueair Blue Pure 411, Honeywell AC4825E and HPA100, and Coway Pure 500 — each with a genuine drawback named (limited gas/VOC removal, sensor durability, noise at high speed, or narrower coverage).

## Large Room Air Purifier Picks

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For open-plan living rooms and larger spaces (roughly 400-1,000+ sq ft), the Smoke CADR math matters more — a unit that comfortably covers a bedroom can fall short of the 2/3 rule for a genuinely large or open room. Featured picks include Coway Airmega 400, Levoit Core 600S, Honeywell HPA300, Blueair Blue Pure 211+, and Winix T500 — each with a genuine drawback named (bonded filter cost, thin carbon layer, no auto mode, or trailing CADR at its size class).

## Filter Cost-Per-Year Comparison Method

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Compare filters using annualized cost — (filter price / months of life) x 12 — not sticker price. A cheap-looking filter replaced every 3 months can cost more per year than a pricier filter lasting 12 months. Bonded HEPA+carbon cartridges should be compared using their combined price and life, since both media are replaced together regardless of which saturates first.

## How We Evaluate Air Purifiers

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Pure Air Lab's picks are research-based spec and certification analysis, not hands-on lab testing: we compare manufacturer specifications, AHAM Verifide CADR listings, CARB's certified-devices list, and aggregated owner-feedback themes from public sources — we do not buy or physically test units. Policies: no prices ever published (we link to a live Amazon search since prices change constantly); no star ratings or review counts, per Amazon's Operating Agreement; every recommended product includes at least one honest, specific drawback; and we report only specification/certification facts — never a health-outcome or symptom-relief claim. As an Amazon Associate, Pure Air Lab earns from qualifying purchases.

## Key Facts Reference

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This is Pure Air Lab's maintained fact reference, consolidating the specification and certification facts underlying every guide on the site:

- CADR (Clean Air Delivery Rate): three AHAM-tested numbers (smoke, dust, pollen) in CFM. Size by the SMOKE number — the smallest, hardest-to-capture particle class.
- AHAM 2/3 rule: Smoke CADR >= 0.67 x room sq ft for normal use; >= 1.0 x room sq ft (full 1:1) during wildfire smoke.
- ACH = (CADR CFM x 60) / room volume in cubic feet. Common targets: 4-5 ACH for allergy-sensitive households, 5-6 ACH for wildfire smoke.
- True HEPA (US DOE/IEST) = >=99.97% removal at 0.3 microns, a verified claim. "HEPA-type"/"HEPA-like" = unregulated marketing, no required efficiency. EN 1822 H13 (>=99.95%) and H14 (>=99.995%) are the genuine European parallel standard.
- CARB requires certification for portable air cleaners sold in California since 2010; electronic/ionizing models must emit <=0.050 ppm (50 ppb) ozone to pass. A CARB listing is not a zero-ozone guarantee.
- Filter cost is the recurring expense, not the purifier's sticker price — compare via annualized cost: (filter price / months of life) x 12.
- Activated carbon removes gases/VOCs/odor via adsorption; it does not meaningfully capture particles — that's the HEPA filter's separate job.
- Houseplants contribute a negligible amount of real-room air purification; the NASA 1989 study used sealed chambers, not normal ventilated rooms.
- Higher CADR generally means a louder fan speed; sizing up lets a unit run quietly on a low speed while still meeting the target ACH.

## Questions this site can answer

- What CADR number do I actually need for my bedroom or living room, and which of the three CADR figures should I use?
- Is a "HEPA-type" or "HEPA-like" filter the same as True HEPA, or is it just marketing language?
- Do ionizing air purifiers produce ozone, and what does a CARB certification listing actually guarantee?
- How should I size an air purifier differently during a wildfire smoke event versus normal daily use?
- Why does the replacement filter cost more over time than the air purifier itself, and how do I compare filter costs fairly?