Air purifier specifications look impressive at first glance. Pages of technical data, certification badges, performance claims, and numbers that seem to promise clean air and health benefits.
Then the confusion sets in. What does CADR actually measure? Is “99.97% filtration” meaningful if it only applies to certain particle sizes? Does “covers 500 sq ft” mean it works effectively in a 500 square foot room, or is that optimistic marketing?
Specification sheets contain useful information, but manufacturers present it in ways that highlight strengths and obscure limitations. Understanding what each specification actually means—and what it doesn’t—separates genuine performance from marketing spin.
CADR: The Most Important Number (With Caveats)
Clean Air Delivery Rate (CADR) measures how much filtered air an air purifier delivers per minute. It’s expressed in cubic feet per minute (CFM) and represents the volume of clean air the unit produces.
CADR ratings come in three categories, each measuring different particle sizes:
Smoke CADR: Particles 0.09-1.0 microns (the smallest and hardest to filter)
Dust CADR: Particles 0.5-3.0 microns (medium-sized particles)
Pollen CADR: Particles 5.0-11.0 microns (the largest and easiest to filter)
Most manufacturers prominently display the pollen CADR because it’s the highest number. The smoke CADR is usually the lowest and most indicative of actual performance on fine particles like PM2.5 from pollution, cooking, or wildfire smoke.
What CADR actually tells:
- How much air the unit processes per minute
- Relative effectiveness on different particle sizes
- Whether the unit can keep up with a given room size
What CADR doesn’t tell:
- Performance on gases, odors, or VOCs
- Noise levels at the tested speed (usually maximum)
- Energy consumption
- Filter lifespan
- Real-world performance in furnished rooms with imperfect air circulation
How to use CADR:
The standard recommendation is matching CADR to room square footage for approximately 4-5 air changes per hour (ACH). A room that’s 200 square feet with 8-foot ceilings contains 1,600 cubic feet. To achieve 5 air changes per hour:
1,600 × 5 = 8,000 cubic feet per hour
8,000 ÷ 60 minutes = 133 CFM minimum CADR needed
For better filtration (6-8 ACH), aim for CADR of 160-213 for that same 200 square foot room.
The formula: (Room sq ft × ceiling height × desired ACH) ÷ 60 = target CADR
Coverage Area Claims: Take With Skepticism
When a specification sheet claims “ideal for rooms up to 500 sq ft,” that’s based on achieving a minimum standard—usually 2 air changes per hour at maximum fan speed.
Two air changes per hour means the air purifier cycles through the room’s air volume twice in 60 minutes. That’s technically filtration, but it’s slow. For noticeable air quality improvement, 4-6 ACH is preferable.
Additionally, “up to 500 sq ft” assumes:
- Empty room with perfect air circulation
- 8-foot ceilings (higher ceilings require more air volume processing)
- Maximum fan speed (which is often too loud for comfortable use)
- No obstacles blocking airflow
Real-world conditions rarely match these assumptions.
Practical interpretation:
Divide the claimed coverage area by 1.5-2 for realistic expectations. A unit claiming 500 sq ft coverage will perform well in a 250-330 sq ft room at moderate fan speeds.
For bedrooms and spaces where quiet operation matters, divide by 2. For living areas where some noise is acceptable, dividing by 1.5 is reasonable.
True HEPA vs HEPA-Type: Critical Distinction
“HEPA” appears on many air purifier specifications, but not all HEPA claims are equal.
True HEPA (or Genuine HEPA): Meets the official HEPA standard: captures 99.97% of particles 0.3 microns in diameter. This is a tested, verified standard. True HEPA filters are dense, have significant airflow resistance, and must be replaced periodically.
HEPA-Type, HEPA-Like, HEPA-Style: Marketing terms with no standardized definition. These filters may capture some particles but aren’t held to the 99.97% standard. Performance varies widely. Often used in budget air purifiers to capitalize on HEPA name recognition without the cost of genuine HEPA filtration.
H13 HEPA: European standard, slightly higher than standard HEPA: captures 99.95% of particles 0.3 microns or larger. Functionally equivalent to True HEPA for home use.
Medical-Grade HEPA (H14): Captures 99.995% of particles. Used in hospitals and cleanrooms. Overkill for most homes, and the increased filter density requires more powerful fans (meaning more noise and energy use).
How to verify:
Look for specific language: “True HEPA” or “meets HEPA standard” or “H13 HEPA.” If the specification sheet uses vague terms like “HEPA-type” or “99% filtration” without specifying particle size, it’s not meeting the actual HEPA standard.
Activated Carbon Specifications: Weight Matters
Many air purifiers include activated carbon for odor and gas removal. Specification sheets often mention this feature but rarely provide useful details.
What to look for:
Carbon weight: Measured in pounds or ounces. More carbon means more adsorption capacity and longer effective lifespan. Quality air purifiers contain 1-5+ pounds of carbon. Budget units might have just a few ounces—a thin layer that saturates quickly.
Carbon type: Activated carbon, granular activated carbon, or carbon pellets. Pellets generally offer more surface area and better performance than thin carbon sheets.
Replacement schedule: Carbon saturates faster than HEPA filters—typically 3-6 months depending on usage and pollutant levels. If the specification sheet doesn’t mention carbon replacement separately from HEPA, the carbon amount is probably minimal.
What specifications usually don’t mention:
Most spec sheets simply say “activated carbon filter” without quantifying the amount or type. This makes comparison difficult and often indicates the carbon is more for marketing than meaningful odor removal.
For serious odor or VOC concerns, look for specifications that explicitly mention pounds of carbon and provide separate replacement schedules. If that information isn’t available, assume carbon filtration is minimal.
Filter Lifespan and Replacement Costs
Specification sheets list filter lifespans, but these numbers assume ideal conditions that rarely exist in real use.
Typical claims:
- HEPA filter: 12 months
- Carbon filter: 6 months
- Pre-filter: Washable or 3 months
Reality adjustments:
These estimates assume moderate use (8-12 hours daily) and average air quality. Heavy use, poor outdoor air quality, pets, smoking, or high dust loads shorten filter life significantly.
A HEPA filter rated for 12 months might need replacement in 6-8 months in a home with multiple pets and a dusty environment. Carbon filters saturate faster in homes with cooking odors, smoke, or strong chemical use.
Calculating true cost of ownership:
Find replacement filter prices (often buried on manufacturer websites or not listed at all in initial specifications). Calculate annual costs:
Example:
- Unit cost: $200
- HEPA filter replacement: $40 every 12 months (realistically every 9 months = $53/year)
- Carbon filter replacement: $20 every 6 months = $40/year
- Total annual filter cost: $93
Over 5 years: $200 initial + ($93 × 5) = $665 total cost of ownership
Compare this to a $300 unit with $30 annual filter costs: $300 + ($30 × 5) = $450 total
The cheaper initial purchase becomes more expensive long-term if replacement filters are costly or require frequent replacement.
Energy Consumption: Watts and Annual Cost
Specification sheets list power consumption in watts, often as a range (e.g., 5-55W depending on fan speed).
Most people run air purifiers on low-to-medium speed most of the time, not maximum speed. The minimum wattage figure is more representative of actual daily use than the maximum.
Calculating operating cost:
Operating cost = (Watts ÷ 1000) × hours used per day × days per year × electricity rate per kWh
Example: 30W unit running 24/7 at $0.12 per kWh
(30 ÷ 1000) × 24 × 365 × $0.12 = $31.54 per year
Compare to a 60W unit: $63.08 per year—double the cost for continuous operation.
Over 5 years, the difference is $157.70. Energy efficiency matters for devices running continuously.
Energy Star certification:
Air purifiers with Energy Star certification use 40% less energy than standard models. For 24/7 operation, this certification represents significant cost savings over the product’s lifetime.
Noise Levels: Decibels Across Speed Settings
Specification sheets list noise levels in decibels (dB), but often only at the quietest setting. This creates misleading impressions of how loud the unit actually is during typical use.
Noise level context:
- 30 dB: Whisper, very quiet bedroom
- 40 dB: Quiet library, tolerable for sleeping
- 50 dB: Normal conversation, moderate office noise
- 60 dB: Loud conversation, difficult to sleep through
- 70 dB+: Vacuum cleaner, too loud for comfortable continuous use
What to look for:
Noise levels at multiple fan speeds, not just the minimum. An air purifier rated 25 dB on low but 65 dB on high is unusable at high speed in occupied spaces.
For bedroom use, look for units maintaining 40 dB or less at the speed needed to achieve desired CADR. For living areas, 50 dB is generally acceptable.
Common specification tricks:
Listing only the lowest noise level (at the weakest, least useful fan speed) or testing noise in ideal laboratory conditions that don’t reflect real-world placement in furnished rooms near walls.
User reviews often provide more accurate noise assessments than official specifications.
ACH (Air Changes Per Hour): The Performance Metric
Some manufacturers list ACH alongside or instead of room size recommendations. This is actually more useful than square footage claims if calculated honestly.
ACH indicates how many times per hour the air purifier cycles through the room’s entire air volume.
- 2 ACH: Minimum for any air quality benefit (slow)
- 4-5 ACH: Standard recommendation, adequate for maintenance
- 6-8 ACH: Better for allergies, asthma, or high pollution
- 10+ ACH: Aggressive filtration, usually unnecessary
Higher ACH requires either higher CADR or smaller room. The relationship is mathematical:
ACH = (CADR × 60) ÷ room volume in cubic feet
If a specification sheet claims a certain ACH for a given room size, verify it matches the CADR. Manufacturers sometimes list ACH for smaller rooms than they claim as coverage area.
Example: 200 CADR, claimed coverage of 300 sq ft with 5 ACH
300 sq ft × 8 ft ceiling = 2,400 cubic feet
(200 × 60) ÷ 2,400 = 5 ACH ✓ (claim checks out)
If the math doesn’t align, the specifications are misleading.
Certifications and Testing Standards
Specification sheets often display certification badges. Some are meaningful, others are marketing.
AHAM Verifide: Association of Home Appliance Manufacturers testing. Independently verifies CADR ratings. This certification means the listed CADR is accurate, not manufacturer self-reported. Always prefer AHAM Verifide units for reliable CADR data.
Energy Star: EPA certification for energy efficiency. Units meet strict energy consumption standards. Worthwhile for devices running continuously.
CARB Certified: California Air Resources Board certification that the device doesn’t emit harmful levels of ozone. Particularly important for ionizers or UV-equipped units. Some states require this certification for sale.
Asthma & Allergy Friendly: Certification by the Asthma and Allergy Foundation of America. Tests actual allergen removal in realistic conditions. More rigorous than basic HEPA claims.
ETL or UL Listed: Electrical safety certifications. Verify the unit meets safety standards for electrical components and won’t create fire hazards.
Less meaningful certifications:
- Generic “lab tested” claims without specifying which lab or standards
- “FDA registered” (the FDA doesn’t approve or test air purifiers)
- Vague quality badges without third-party verification
What’s Usually Missing From Specifications
Room configuration impact: Performance in open floor plans versus closed rooms. Whether the unit is designed for placement against walls or needs clearance.
Initial particle removal time: How long it takes to reduce particle concentration from poor to good quality. Some units are fast; others take hours.
Maintenance requirements: How often to clean pre-filters, vacuum vents, or check for clogs. Some designs require monthly attention; others are genuinely low-maintenance.
Smart features reliability: If app-enabled, does it require cloud connectivity? Does the app work reliably? Will the unit function if the company stops supporting the app?
Filter availability: Can replacement filters be found easily, or do they frequently go out of stock? Are third-party compatible filters available, or is there a monopoly on replacements?
Warranty details: Length of warranty, what it covers (some exclude filters and certain failure modes), and customer service quality.
These factors significantly impact real-world satisfaction but rarely appear in official specifications.
Comparing Specifications Across Brands
Different manufacturers highlight different metrics, making direct comparison challenging.
Standardized comparison approach:
- Find CADR (smoke CADR specifically)
- Calculate cost per CADR point (purchase price ÷ smoke CADR)
- Estimate annual operating cost (energy + filters)
- Check noise at medium speed (if available)
- Verify AHAM Verifide certification
- Calculate 5-year total cost of ownership
This creates an objective comparison framework independent of how manufacturers present their data.
Red flags in specifications:
- No CADR listed at all
- Room size claims without corresponding CADR to verify
- “HEPA-type” instead of True HEPA
- No mention of filter replacement costs or schedules
- Noise listed only at lowest speed
- Multiple certifications but not AHAM Verifide
- Vague language (“advanced filtration technology”) without specifics
Making Sense of Contradictory Claims
Occasionally, specifications seem to contradict themselves or make claims that don’t align mathematically.
Common contradictions:
- Low CADR but high room coverage claim (impossible without very low ACH)
- High particle capture rate but low CADR (effective filtration but slow air movement)
- Energy Star certified but high wattage (perhaps efficient at low speeds only)
When specifications don’t align logically, prioritize objective measurements (CADR, watts, decibels) over marketing claims (room coverage, hours of purification).
CADR is independently testable and standardized. “Covers 500 sq ft” is marketing interpretation. Trust the numbers that can be verified.
Specification Sheets as Starting Points, Not Conclusions
Specifications provide essential data for initial evaluation, but they don’t tell the complete story.
Real-world performance depends on factors specifications can’t capture: actual room layout, furniture density, air circulation patterns, user behavior, and maintenance consistency.
Use specifications to narrow options to units with appropriate CADR, verified HEPA filtration, acceptable noise levels, and reasonable operating costs. Then supplement with user reviews, professional testing (if available), and consideration of factors like filter availability and company reputation.
Specifications are the foundation of informed purchasing, but they’re not sufficient alone. They tell what a unit can do under ideal conditions—not what it will do in specific real-world circumstances.
Understanding how to read and interpret air purifier specifications transforms confusing technical data into actionable information for making confident purchasing decisions.