🌬️ HEPA Filters & CADR: Your Complete Air Purification Guide

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What You'll Learn

Master HEPA filter technology, decode CADR ratings, understand particle sizes, and discover how to choose the perfect air purifier for your room size and air quality needs.

💡 Quick Summary

? What is HEPA & CADR?

HEPA filters remove 99.97% of particles ≥0.3 microns. CADR (Clean Air Delivery Rate) measures how quickly an air purifier cleans specific particle types.

✓ Why It Matters

Proper HEPA+CADR matching ensures effective removal of PM2.5, allergens, and pollutants. Wrong sizing can leave 40-60% of room air uncleaned.

🎯 1. Understanding HEPA Filter Technology

The Gold Standard of Filtration

HEPA (High-Efficiency Particulate Air) filters are the most effective mechanical filters available for home use, capable of capturing particles invisible to the naked eye.

🔬 HEPA Filtration Science

1 Impaction

Large particles (>1 micron) crash into fibers and stick due to inertia

2 Interception

Medium particles (0.3-1 micron) follow airflow but get caught when they pass close to fibers

3 Diffusion

Tiny particles (<0.3 micron) move erratically and eventually collide with fibers

📊 HEPA Filter Classification

True HEPA

H13/H14 Grade

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Efficiency: 99.95-99.995%
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Particle size: ≥0.3 microns
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Certification: Tested & verified

Best for: Medical-grade air purification

HEPA-type

H10/H11 Grade

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Efficiency: 85-95%
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Particle size: ≥0.3 microns
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Certification: Limited testing

Best for: Budget air purifiers

HEPA-like

Marketing Term

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Efficiency: 50-85%
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Particle size: Various
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Certification: None required

Avoid: Not true HEPA performance

🦠 Particle Size Reference Guide

Particle Type	Size (Microns)	HEPA Effective	Health Impact
Human Hair	50-100	✓ 99.99%	Visible, non-harmful
Pollen	10-100	✓ 99.99%	Allergenic
Dust Mites	10-40	✓ 99.99%	Allergenic
PM10	2.5-10	✓ 99.97%	Respiratory irritation
PM2.5	0.1-2.5	✓ 99.95%	Deep lung penetration
Bacteria	0.3-5	✓ 99.97%	Infectious diseases
Viruses	0.01-0.3	~ 85-95%	Various infections

💡 Note: While HEPA filters are very effective against viruses, they're often attached to larger particles (droplets) making them easier to capture.

📏 2. CADR Rating: Measuring Real-World Performance

Speed Matters as Much as Efficiency

CADR (Clean Air Delivery Rate) measures how quickly an air purifier can clean specific types of particles from room air, combining both filtration efficiency and airflow rate.

🧮 Understanding CADR Numbers

CADR = Air Volume × Filter Efficiency

Measured in CFM (cubic feet per minute) or m³/h

High CADR

Fast cleaning, large rooms

Medium CADR

Balanced performance

Low CADR

Slow cleaning, small rooms

🌸 Pollen CADR

• Large particles (10-100 microns)
• Easiest to filter
• Highest CADR values
• Important for allergies

💨 Dust CADR

• Medium particles (0.5-3 microns)
• Moderate difficulty to filter
• Middle CADR values
• General air quality

🚬 Smoke CADR

• Tiny particles (0.01-1 micron)
• Hardest to filter
• Lowest CADR values
• Critical for PM2.5

🏠 Room Size vs CADR Requirements

150-250 CFM

Small Rooms

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Room size: 100-200 sq ft
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Examples: Bedroom, study
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Air changes: 4-5 per hour

Ideal for: Personal air purification

250-400 CFM

Medium Rooms

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Room size: 200-350 sq ft
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Examples: Master bedroom, living room
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Air changes: 4-5 per hour

Ideal for: Family rooms, offices

400-600 CFM

Large Rooms

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Room size: 350-500 sq ft
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Examples: Open living area, hall
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Air changes: 4-5 per hour

Ideal for: Open floor plans

600+ CFM

Very Large Spaces

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Room size: 500+ sq ft
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Examples: Great rooms, offices
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Air changes: 4-5 per hour

Ideal for: Commercial spaces

🏠 Real-World Example

Delhi Family's Air Purifier Selection

The Gupta family needs an air purifier for their 300 sq ft living room during Delhi's pollution season.

📐 Room Requirements

• Room: 15' × 20' × 9' = 2,700 cubic feet
• Target: 5 air changes per hour
• Required CADR: 2,700 ÷ 60 × 5 = 225 CFM
• Delhi pollution focus: Smoke CADR critical

✅ Selected Air Purifier

• Smoke CADR: 240 CFM (exceeds requirement)
• True HEPA H13 filter (99.95% efficient)
• Result: Clean air every 12 minutes
• PM2.5 levels dropped from 150 to <25 μg/m³

💡 Takeaway: Matching CADR to room size with focus on the most relevant particle type (smoke for PM2.5) ensures optimal air quality improvement.

🔧 3. Advanced Filtration Technologies

Beyond Basic HEPA

Modern air purifiers combine HEPA with additional technologies to tackle odors, gases, and ultra-fine particles that HEPA alone cannot handle.

🔄 Multi-Stage Filtration Systems

Pre-Filter

Captures large particles (hair, dust, pet fur) to extend HEPA life

Efficiency: 80-90% for particles >10 microns | Washable: Usually yes

Activated Carbon Filter

Absorbs odors, VOCs, and gaseous pollutants

Target: Cooking smells, smoke, chemicals | Replacement: 3-6 months

True HEPA Filter

Primary filtration for particles ≥0.3 microns

Efficiency: 99.97% for ≥0.3 microns | Replacement: 6-12 months

UV-C or Ionizer (Optional)

Additional sterilization or particle charging

Purpose: Kill bacteria/viruses or enhance particle capture

⚗️ Additional Technologies Comparison

✅ Proven Technologies

Activated Carbon

Excellent for odors, VOCs, and gases. Proven and safe.

UV-C Light

Effective against viruses and bacteria when properly designed.

Photocatalytic Oxidation (PCO)

Breaks down VOCs and odors at molecular level.

⚠️ Technologies to Research Carefully

Ionizers/Negative Ion

Can produce ozone; effectiveness varies greatly.

Ozone Generators

Ozone is a lung irritant; avoid for occupied spaces.

Electrostatic Precipitators

Require frequent cleaning; can produce ozone.

🛒 4. Smart Buying Decisions

Making the Right Choice

Use HEPA certification and CADR ratings to select an air purifier that matches your specific room size and air quality challenges.

🛒 How This Affects Your Purchase Decision

🎯 What to Look For

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True HEPA certification (H13/H14)
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CADR rating ≥4x room volume for 5 air changes/hour
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Smoke CADR for PM2.5 concerns
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Multiple fan speeds for efficiency
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Filter replacement indicators

⚠️ Red Flags to Avoid

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"HEPA-like" or "HEPA-type" without certification
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No CADR ratings provided
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Claims of >99.99% efficiency without testing proof
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Ozone generation as a "feature"
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Very high CADR claims at suspiciously low prices

💡 Selection Decision Tree

🏭 High Pollution Areas (AQI >150)

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Focus on high smoke CADR (PM2.5 removal)
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True HEPA H14 preferred over H13
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Consider 6+ air changes per hour
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24/7 operation capability important
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Low noise levels for continuous use

🌿 Allergy & Asthma Management

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High pollen and dust CADR ratings
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True HEPA with H13 minimum
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Activated carbon for pet odors
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No ozone or ion generation
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Easy filter replacement for maintenance

💰 Cost of Ownership Analysis

Cost Component	Year 1	Year 2-3	Annual Ongoing
Initial Purchase	₹15,000-50,000	-	-
HEPA Filter	Included	₹2,000-4,000	₹2,000-4,000
Carbon Filter	₹500-1,500	₹1,000-3,000	₹1,000-3,000
Electricity (24/7)	₹1,500-3,000	₹1,500-3,000	₹1,500-3,000
Total Annual Cost	₹17,000-55,000	₹4,500-10,000	₹4,500-10,000

💡 Budget Tip: Factor in 5-year total cost when comparing models. Higher-quality filters may cost more initially but often last longer and perform better.

❓ Frequently Asked Questions

Quick Answers

Common questions about HEPA filters and CADR ratings answered simply

Q: Do I need True HEPA or is HEPA-type sufficient?

For serious air quality concerns (pollution, allergies), True HEPA (99.97% efficiency) is essential. HEPA-type (85-95%) may be adequate for light dust control but won't handle PM2.5 or allergens effectively.

Q: Which CADR rating should I focus on - dust, pollen, or smoke?

Focus on smoke CADR for PM2.5 and general air quality. Pollen CADR for allergies. Smoke particles are the hardest to filter, so if smoke CADR is adequate, the purifier will handle larger particles well.

Q: How often do HEPA filters need replacement?

Typically 6-12 months depending on air quality and usage. In high-pollution areas like Delhi, expect 6-8 months. Clean pre-filters monthly to extend HEPA life. Follow manufacturer guidelines and filter indicators.

Q: Can I wash and reuse HEPA filters?

No. True HEPA filters cannot be washed - it destroys the fiber structure and eliminates filtration effectiveness. Only pre-filters are typically washable. Replace HEPA filters as recommended for continued protection.

Q: Do higher CADR ratings mean louder operation?

Not necessarily. Look for multiple fan speeds - higher CADR models often have better motors and fan design. Check noise levels at different speeds. Many high-CADR purifiers are quiet on low settings for nighttime use.

Q: Are expensive HEPA filters always better than cheaper ones?

Not always. Focus on certification (H13/H14), appropriate CADR for your room, and total cost of ownership including filter replacements. Some budget models with genuine HEPA can outperform expensive models with marketing fluff.

📚 Related Resources

Complete Air Purifier Guide

Choose the perfect air purifier for your needs

Hard Water 101

Understanding water quality and filtration

Best Air Purifiers 2025

Top-rated air purifier recommendations

⚠️ Disclaimer: HEPA efficiency and CADR ratings are based on laboratory testing conditions and may vary with actual usage. Always check for current certifications and follow manufacturer maintenance guidelines. This guide is for educational purposes only.

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