When shopping for an air purifier, you’ll encounter numerous technical specifications and ratings that can be overwhelming. These numbers aren’t just marketing jargon—they provide crucial information about performance, efficiency, and suitability for your needs. From CADR ratings to HEPA classifications, ACH rates to decibel levels, understanding these metrics helps you make an informed purchase decision. Air purifier numbers directly translate to real-world performance and can mean the difference between effective air cleaning and wasted investment. This guide breaks down the essential numbers you’ll encounter and explains what they mean for your indoor air quality.
CADR (Clean Air Delivery Rate) is perhaps the most important number to understand when evaluating air purifiers. Developed by the Association of Home Appliance Manufacturers (AHAM), CADR measures how quickly an air purifier can filter specific pollutants from the air in a controlled test environment. The higher the CADR number, the faster the unit cleans the air.
CADR ratings are typically provided for three pollutant categories: tobacco smoke (0.09-1.0 microns), dust (0.5-3.0 microns), and pollen (5.0-11.0 microns). The ratings are expressed in cubic feet per minute (CFM) or cubic meters per hour (m³/h), representing the volume of filtered air delivered.
| CADR Rating Range | Room Size Suitability | Performance Level |
|---|---|---|
| 0-100 CFM | Small rooms (up to 150 sq ft) | Basic |
| 100-200 CFM | Medium rooms (150-300 sq ft) | Good |
| 200-350 CFM | Large rooms (300-500 sq ft) | Very Good |
| 350+ CFM | Extra large spaces (500+ sq ft) | Excellent |
A general rule of thumb: for effective air cleaning, choose an air purifier with a CADR rating that’s at least two-thirds of your room’s square footage. For example, a 300 square foot room would benefit from a purifier with a CADR of at least 200.
MERV Ratings: Filter Efficiency Measurement
MERV (Minimum Efficiency Reporting Value) rates the effectiveness of air filters on a scale of 1-20. Higher MERV ratings indicate superior filtration capabilities for capturing smaller particles. While MERV primarily applies to HVAC systems, understanding these ratings helps contextualize air purifier performance.
Most residential air purifiers utilize filters equivalent to MERV 8-13, while medical-grade purifiers may use filters comparable to MERV 14-16. HEPA filters, the gold standard in air purification, generally exceed the MERV scale, performing better than MERV 16.
| MERV Rating | Particle Size Filtered | Applications |
|---|---|---|
| 1-4 | ≥ 10.0 microns | Basic residential, minimal filtration |
| 5-8 | 3.0-10.0 microns | Better residential, light commercial |
| 9-12 | 1.0-3.0 microns | Superior residential, commercial, industrial |
| 13-16 | 0.3-1.0 microns | Hospital laboratories, general surgery |
| 17-20 | Cleanrooms, pharmaceutical manufacturing |
HEPA Classifications: Understanding Filtration Efficiency
HEPA (High-Efficiency Particulate Air) filters are classified based on their efficiency in capturing particles. True HEPA filters must capture at least 99.97% of particles at 0.3 microns in size—the most penetrating particle size and therefore the most difficult to capture.
European standards classify HEPA filters from H10 to H14, while the newer ISO 29463 standard uses classifications from ISO 15E to ISO 50U. Understanding these classifications helps determine if an air purifier meets your specific air quality needs.
| HEPA Class | Filtration Efficiency | Particles Captured |
|---|---|---|
| H10 (ISO 15E) | 85% | Basic filtration, not True HEPA |
| H11 (ISO 20E) | 95% | Better filtration, not True HEPA |
| H12 (ISO 25E) | 99.5% | Close to True HEPA standards |
| H13 (ISO 35H) | 99.95% | True HEPA, residential and medical |
| H14 (ISO 45H) | 99.995% | Highest HEPA grade, medical and cleanrooms |
When manufacturers list terms like “HEPA-type” or “HEPA-like,” these often don’t meet true HEPA standards. For allergy and asthma sufferers, genuine H13 filters or higher provide the most reliable air purification performance.
ACH Rate: Air Changes Per Hour
ACH (Air Changes Per Hour) indicates how many times an air purifier can filter the entire volume of air in a room each hour. Higher ACH rates mean more frequent air cleaning, which is particularly important for allergies, asthma, or in rooms with higher pollutant levels.
For general home use, an ACH of 4-5 is considered good. This means the entire volume of air in the room is filtered 4-5 times every hour. For people with respiratory conditions or in environments with poor air quality, higher ACH rates of 6-8 are recommended.
- ACH 2-3: Minimum for general air maintenance in homes
- ACH 4-5: Recommended for most residential applications
- ACH 6-8: Ideal for allergies, asthma, or poor outdoor air quality
- ACH 8+: Medical settings, extreme allergies, or contamination concerns
Keep in mind that the advertised ACH rate applies to the recommended room size. If you place an air purifier in a larger space than recommended, the actual ACH rate will be lower than specified.
PM Ratings: Understanding Particulate Matter Measurements
Smart air purifiers often display PM (Particulate Matter) readings, which indicate the concentration of airborne particles by size. The most common measurements are PM2.5 and PM10, representing particles smaller than 2.5 microns and 10 microns respectively.
PM2.5 particles are especially concerning as they can penetrate deep into lungs and even enter the bloodstream. The World Health Organization and EPA have established guidelines for safe PM levels, which many air purifiers use as reference points for their air quality indicators.
| PM2.5 Level (μg/m³) | Air Quality Category | Health Implications |
|---|---|---|
| 0-12 | Good | Little to no risk |
| 12.1-35.4 | Moderate | Acceptable for most individuals |
| 35.5-55.4 | Unhealthy for Sensitive Groups | May affect people with respiratory conditions |
| 55.5-150.4 | Unhealthy | Everyone may experience health effects |
| 150.5+ | Very Unhealthy to Hazardous | Serious health effects for all |
Some advanced air purifiers automatically adjust their fan speed based on detected PM levels, increasing filtration when air quality deteriorates and conserving energy when air quality is good.
Coverage Area: Room Size Specifications
Manufacturers typically specify the maximum room size their air purifiers can effectively clean, measured in square feet or square meters. This number is calculated based on the unit’s CADR rating and an assumed ceiling height (usually 8 feet).
It’s important to understand that the coverage area specification typically assumes an ACH rate of 2, which may be insufficient for people with respiratory sensitivities. For higher ACH rates, the effective coverage area decreases proportionally.
| Desired ACH | Coverage Area Adjustment |
|---|---|
| 2 ACH | 100% of rated coverage area |
| 4 ACH | 50% of rated coverage area |
| 6 ACH | 33% of rated coverage area |
| 8 ACH | 25% of rated coverage area |
For example, if an air purifier claims to cover 300 square feet, but you need 4 air changes per hour for allergies, the effective coverage drops to 150 square feet. Always choose an air purifier that exceeds your room size needs to ensure optimal air cleaning performance.
Filter Life Indicators: Replacement Timing
Air purifiers indicate filter life through various metrics such as hours of operation, months of use, or more sophisticated sensors that detect filter saturation. These numbers are crucial for maintaining optimal performance as clogged filters significantly reduce air cleaning efficiency.
Most HEPA filters last between 6-12 months depending on usage and air quality conditions. Carbon filters typically have shorter lifespans, often 3-6 months. Pre-filters may need cleaning or replacement every 1-3 months to ensure proper airflow.
- Basic indicators: Simple time-based counters that track months or hours of operation
- Mid-range indicators: Take into account both time and fan speed usage
- Advanced indicators: Use pressure differential sensors to detect actual filter saturation
- Smart indicators: Consider usage patterns, air quality readings, and even humidity levels
Some high-end purifiers provide percentage indicators showing remaining filter capacity, while others use color-coded systems (green/yellow/red) to signal when filter replacement is approaching or overdue.
Noise Level Measurements: Decibel Ratings
Air purifier noise levels are measured in decibels (dB), typically ranging from around 20dB on the lowest setting to 60dB or higher at maximum speed. Lower decibel numbers indicate quieter operation, which is particularly important for bedrooms, offices, or other noise-sensitive environments.
| Decibel Range | Noise Equivalent | Suitability |
|---|---|---|
| 20-30 dB | Whisper, rustling leaves | Ideal for bedrooms, nurseries |
| 30-40 dB | Quiet library, soft conversation | Good for bedrooms, offices |
| 40-50 dB | Refrigerator hum, quiet office | Acceptable for living rooms, kitchens |
| 50-60 dB | Normal conversation, dishwasher | May be distracting in quiet environments |
| 60+ dB | Vacuum cleaner, busy traffic | Potentially disruptive, suitable only for temporary use |
Note that many manufacturers list only the lowest noise level in their marketing materials. For a complete understanding, look for noise ratings across all fan speeds. Sleep modes on modern air purifiers typically operate below 30dB, allowing for uninterrupted sleep while maintaining some level of air cleaning.
Energy Consumption Ratings: Power Usage
Air purifier energy consumption is typically measured in watts (W), with most residential models using between 5W and 100W depending on the fan speed. Lower wattage means lower electricity costs but may indicate reduced air cleaning power.
Some air purifiers feature the ENERGY STAR certification, indicating they meet strict energy efficiency guidelines established by the EPA. These models are typically 25-40% more energy-efficient than standard models without sacrificing performance.
| Power Consumption | Energy Efficiency | Annual Cost Estimate (24/7 operation) |
|---|---|---|
| 5-20W | Very efficient | $5-$20 |
| 20-40W | Efficient | $20-$40 |
| 40-60W | Moderate | $40-$60 |
| 60-100W | Less efficient | $60-$100 |
| 100W+ | High consumption | $100+ |
Many modern air purifiers include automatic modes that adjust fan speeds based on detected air quality, thereby optimizing energy usage. Smart models can be programmed to run on schedules or remotely controlled to operate only when needed, further reducing energy consumption.
AHAM Verifide Program: Independent Testing Certification
The AHAM Verifide program provides independent testing and certification of air purifier performance claims. When you see the AHAM Verifide seal, it indicates the CADR ratings have been independently verified rather than just claimed by the manufacturer.
This certification includes testing for the three main CADR measurements (smoke, dust, and pollen) as well as the suggested room size based on those ratings. For consumers seeking reliable performance data, the AHAM Verifide seal offers a measure of confidence in manufacturer claims.
- Verified CADR ratings: Independently tested performance figures
- Suggested room size: Based on 2 air changes per hour calculation
- Testing standardization: All certified models tested under identical conditions
- Regular verification: Ongoing testing to ensure continued compliance
Not all air purifiers participate in the AHAM certification program, but those that do typically display the Verifide seal on their packaging and in product listings. While uncertified models aren’t necessarily inferior, they lack the independent verification that certified models provide.
How to Use Air Purifier Numbers for Comparison Shopping
When comparing air purifiers, focus on the specifications most relevant to your specific needs. CADR ratings and coverage area should be your primary considerations, followed by filter type, noise levels, and energy efficiency.
For allergies or asthma, prioritize models with high CADR ratings for the particles that trigger your symptoms (typically dust and pollen), true HEPA filtration (H13 or better), and an ACH rate of at least 4-5 for your room size.
| Priority Concern | Primary Specifications to Compare |
|---|---|
| General air quality | CADR ratings, coverage area, filter type |
| Allergies/Asthma | HEPA classification, ACH rate, CADR for pollen/dust |
| Odors/Chemicals | Carbon filter weight/type, CADR for smoke |
| Bedroom use | Noise levels (dB), night mode features, light dimming |
| Energy concerns | Wattage, ENERGY STAR certification, auto modes |
Be wary of marketing terms like “HEPA-type” or proprietary rating systems that can’t be directly compared across brands. Independently verified metrics provide the most reliable basis for comparison when evaluating different air purifier models.