AC Tonnage vs BTU vs CFM: Sizing Without Guesswork
Master AC sizing with our complete guide to tonnage, BTU, and CFM ratings. Learn the exact formulas and sizing charts to choose the perfect air conditioner capacity for any room size in India.
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Technical Guide
Technical explanation
📋 AC Tonnage vs BTU vs CFM: Sizing Without Guesswork
What You'll Learn
Master the three critical AC measurements that determine cooling performance. Learn exact conversion formulas, room sizing charts, and CFM requirements to choose the perfect air conditioner capacity without any guesswork.
💡 Quick Summary
? What is AC Tonnage?
Tonnage measures cooling capacity. 1 Ton = 12,000 BTU/hr cooling power.
✓ Why BTU Matters
BTU (British Thermal Unit) is the actual energy measurement for cooling power.
≈ CFM Explained
CFM (Cubic Feet per Minute) measures airflow - critical for even cooling.
🎯 1. Understanding AC Tonnage
The Foundation of AC Sizing
Tonnage is the most common way to describe AC capacity in India, but what does it actually measure?
🔧 AC Tonnage Explained
1 Historical Origin
Originally based on ice cooling - 1 ton = cooling power of 1 ton of ice melting in 24 hours
2 Modern Definition
1 Ton = 12,000 BTU per hour of cooling capacity - industry standard worldwide
3 Practical Usage
Easy reference for consumers - simpler than saying "12,000 BTU/hr cooling capacity"
⭐ Standard AC Tonnage Ratings in India
1.0 Ton AC (12,000 BTU/hr)
Most common residential size, perfect for bedrooms and small living areas
1.5 Ton AC (18,000 BTU/hr)
Popular choice for medium-sized rooms and master bedrooms
2.0 Ton AC (24,000 BTU/hr)
Heavy-duty cooling for large living rooms and commercial spaces
🌡️ 2. BTU: The Real Cooling Power
Beyond Tonnage: Understanding True Capacity
BTU is the actual scientific measurement of cooling power - here's why it matters more than tonnage
🔬 What BTU Actually Measures
British Thermal Unit Definition
1 BTU = Energy needed to raise 1 pound of water by 1°F at sea level
📊 Why BTU Matters
- • Precise measurement of cooling capacity
- • Universal standard across all countries
- • Allows exact comparison between models
- • Determines actual energy consumption
🔄 BTU vs Tonnage
- • Tonnage is simplified consumer language
- • BTU gives exact cooling power
- • Some "1.5 ton" ACs vary in actual BTU
- • BTU rating determines room sizing
📊 Exact Tonnage to BTU Conversions
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BTU/hr: 12,000
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Room Size: Up to 120 sq ft
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Power Draw: ~900-1200W
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BTU/hr: 18,000
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Room Size: 121-180 sq ft
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Power Draw: ~1400-1800W
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BTU/hr: 24,000
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Room Size: 181-250 sq ft
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Power Draw: ~1900-2400W
💨 3. CFM: The Forgotten Third Factor
Airflow: The Key to Even Cooling
CFM determines how well your AC distributes cool air - often more important than raw cooling power
🌬️ Understanding CFM (Cubic Feet per Minute)
What CFM Measures
CFM = Volume of air moved per minute by the AC's fan system
Why CFM Matters
🏠 Real-World CFM Example
Two 1.5 Ton ACs, Different CFM Ratings
Both have 18,000 BTU/hr cooling capacity, but very different performance
🔴 AC A: 450 CFM (300 per ton)
- • Cool air stays near indoor unit
- • 5-7°F difference across room
- • Takes longer to cool entire space
- • May need ceiling fan assistance
🟢 AC B: 650 CFM (433 per ton)
- • Even temperature distribution
- • 1-2°F difference maximum
- • Faster overall cooling
- • Better comfort without fans
📐 4. Room Sizing Without Guesswork
Scientific Room-to-AC Matching
Use these proven formulas and adjustment factors for perfect AC sizing every time
🎯 Base Room Size Guidelines
⚡ Capacity Addition Factors
Add extra capacity for these conditions:
🧮 Sizing Calculator Example
West-Facing Master Bedroom (14×12 ft = 168 sq ft)
Step-by-step AC sizing calculation
📋 Step 1: Base Requirement
- • Room size: 168 sq ft
- • Base requirement: 1.5 ton (within 121-180 range)
- • Base BTU: 18,000 BTU/hr
⚡ Step 2: Adjustment Factors
- • West-facing: +20% = +3,600 BTU
- • Final requirement: 21,600 BTU/hr
- • Recommendation: 2.0 ton AC
🚫 Common AC Sizing Mistakes
Myth
"Bigger AC will cool faster, so buy 2 ton for any room"
Reality
Oversized ACs cycle frequently, waste energy, and create humidity problems. Right-sizing is crucial for efficiency and comfort.
Myth
"CFM doesn't matter, only tonnage is important"
Reality
CFM determines air distribution. Low CFM creates hot spots even with adequate tonnage. Aim for 350+ CFM per ton.
🛒 How This Affects Your Purchase Decision
🎯 What to Look For
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BTU rating on energy label (not just tonnage)
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CFM specification (aim for 350+ per ton)
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Variable speed compressor for better efficiency
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Multiple fan speeds for airflow control
⚠️ Red Flags to Avoid
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Tonnage ratings without BTU specifications
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Missing CFM data on specification sheets
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Extremely low CFM (under 300 per ton)
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Sales claims without energy label verification
❓ Frequently Asked Questions
Quick Answers
Common questions about AC tonnage, BTU, and CFM answered simply
Q: Can I use a 1.5 ton AC in a 200 sq ft room to save money?
A:
No, this will actually cost more in the long run. An undersized AC will run continuously trying to cool the space, consuming more electricity and wearing out components faster. For 200 sq ft, use a 2.0 ton AC for better efficiency and comfort.
Q: What's the difference between BTU/hr and BTU?
A:
BTU/hr (British Thermal Units per hour) measures cooling power rate - how much heat the AC can remove per hour. Plain BTU measures total energy. For AC sizing, always look for BTU/hr rating, which tells you the continuous cooling capacity.
Q: Why do some 1.5 ton ACs have different CFM ratings?
A:
CFM depends on the indoor unit's fan design and motor power. Different manufacturers use various fan configurations. Higher CFM usually means better air distribution but may also mean slightly higher power consumption. Look for the sweet spot of 350-450 CFM per ton.
Q: Should I factor in ceiling height for AC sizing?
A:
Yes, for ceiling heights above 10 feet, add 10% extra capacity for every additional foot. A room with 12-foot ceilings needs about 20% more cooling capacity than the same floor area with 8-foot ceilings.
Q: Is tonnage rating the same across all AC brands?
A:
Tonnage is standardized (1 ton = 12,000 BTU/hr), but actual performance can vary. Always check the energy label for exact BTU/hr rating and EER (Energy Efficiency Ratio). Some brands may have slight variations in actual cooling output within the same tonnage category.
🎯 Key Takeaways
This article explains the key concepts behind ac sizing in simple terms for air conditioner buyers.