CADR & Room Sizing for Air Purifiers: Simple Math for Clean Air
Master air purifier sizing with CADR calculations. Learn the ACH formula, room volume math, and exact specifications needed for effective air purification in Indian homes.
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Technical Guide
Technical explanation
📐 CADR & Room Sizing: Simple Math for Clean Air
What You'll Learn
Master the CADR formula, calculate exact room volumes, and determine the perfect air purifier specifications for your space. No more guesswork - just simple math for effective air cleaning.
💡 Quick Summary
📊 CADR Formula
ACH = (CADR × 60) ÷ Room Volume for calculating air changes per hour
🎯 Target ACH
2-3 ACH for general use, 4-5+ ACH for allergies and asthma relief
📏 Room Volume
Length × Width × Height = Room Volume in cubic meters for calculations
📊 1. Understanding CADR (Clean Air Delivery Rate)
The Foundation of Air Purifier Performance
CADR measures how much clean air an air purifier delivers per hour - the most important specification for sizing
🔬 What CADR Actually Measures
CADR Definition
Volume of clean air produced per hour, measured in cubic meters per hour (m³/h) or cubic feet per minute (CFM)
CADR vs Room Size
🔄 CADR Measurement Standards
Dust CADR
Measures effectiveness against 0.5-3 micron particles like dust mites, pet dander
Pollen CADR
Effectiveness against 5-11 micron particles like tree and grass pollen
Smoke CADR
Measures performance against 0.09-1 micron particles like tobacco smoke, PM2.5
🧮 2. The ACH Formula Explained
Air Changes Per Hour: The Key Metric
ACH tells you how many times per hour your air purifier can clean the entire room's air volume
📐 The Complete ACH Formula
Core Formula
Room Volume Calculation
Step-by-Step Calculation
🎯 ACH Targets for Different Needs
Recommended Air Changes Per Hour
General Use
Basic air cleaning for normal indoor air quality maintenance
Allergy Relief
Enhanced cleaning for people with allergies and sensitivities
Medical/Severe Conditions
Maximum air cleaning for severe asthma, COPD, or high pollution areas
🏠 3. Real Room Sizing Examples
Step-by-Step Room Calculations
Practical examples for common Indian room sizes with exact CADR requirements
📏 Common Indian Room Sizes
Small Bedroom
Master Bedroom
Living Room
🧮 DIY CADR Calculator
Calculate Your Room's CADR Requirement
Step 1: Room Dimensions
Step 2: Convert to m³
Step 3: Choose ACH Target
Step 4: Calculate CADR
🛒 4. Practical Buying Considerations
Beyond the Numbers
Real-world factors that affect air purifier performance and CADR effectiveness
⚠️ CADR Reality Check
Why You Need Higher CADR Than Calculated
Performance Factors
- • Filter aging reduces efficiency
- • Dust buildup affects airflow
- • High pollution exceeds capacity
- • Furniture blocks air circulation
Recommendation
Common CADR Mistakes
🛒 How This Affects Your Purchase Decision
🎯 What to Look For
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AHAM verified CADR ratings for dust, pollen, smoke
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CADR specifications at multiple fan speeds
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Room size recommendations that match your calculations
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Energy efficiency ratings and filter replacement costs
⚠️ Red Flags to Avoid
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No specific CADR numbers - only vague "room size" claims
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CADR claims without third-party verification
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Oversized room recommendations vs actual CADR
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No noise level specifications for different speeds
❓ Frequently Asked Questions
Quick Answers
Common questions about CADR calculations and air purifier sizing answered
Q: Should I use dust, pollen, or smoke CADR for sizing calculations?
A:
Use the CADR rating that matches your primary concern. For general air cleaning, use dust CADR. For allergies, use pollen CADR. For urban pollution or cooking smoke, use smoke CADR. When in doubt, use the lowest of the three ratings for conservative sizing.
Q: Can I use one large air purifier instead of multiple smaller ones?
A:
Generally, multiple smaller units provide better air circulation and coverage than one large unit. However, if the room is open-plan and the large unit has sufficient CADR (total room volume × desired ACH ÷ 60), it can work effectively.
Q: How often should I recalculate CADR requirements?
A:
Recalculate when you change rooms, add furniture that significantly blocks airflow, or if your air quality needs change (like developing allergies). Also consider that CADR decreases as filters age, so factor in maintenance schedules.
Q: Do ceiling fans affect the ACH calculation?
A:
Ceiling fans help distribute cleaned air but don't change the CADR requirement. They can improve effectiveness by preventing air stratification, potentially allowing you to achieve target ACH with slightly lower CADR, but it's safer to use the calculated CADR.
Q: Is 2 ACH really enough for general air cleaning?
A:
2-3 ACH is adequate for maintenance cleaning in homes with good baseline air quality. However, in Indian cities with high pollution, or homes with pets, cooking odors, or dust issues, 4-5 ACH provides more noticeable improvement.
🎯 Key Takeaways
This article explains the key concepts behind air purifier-sizing in simple terms for air purifier buyers.