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Why Tonnage Matters

Choosing the right AC tonnage is crucial for efficient cooling and energy saving. An undersized AC will run continuously, leading to high electricity bills and poor cooling. An oversized AC will cool the room too quickly without dehumidifying, making the air feel clammy, and the frequent on-off cycles will wear out the compressor.

Step 1: Calculate Room Size

The first step is to measure the area of your room in square feet. Formula: Length (ft) x Width (ft) = Area (sq ft)

• Up to 120 sq ft: 0.75 - 1 Ton
• 121 - 150 sq ft: 1 - 1.2 Ton
• 151 - 250 sq ft: 1.5 - 2 Ton
• 251 - 400 sq ft: 2 Ton or more

Step 2: Adjust for Ceiling Height

Standard ceiling height is considered 10 feet. If your ceiling is higher than 10 feet, you should slightly increase the required tonnage.

Step 3: Consider Occupancy

People generate heat. The standard calculation assumes 2-3 people in the room.

• If you expect more than 3 people regularly, add 600 BTU/hr for each additional person.

Step 4: Sunlight and Insulation

• Direct Sunlight: If the room gets direct sunlight during the day, increase the capacity by 10%.
• Shaded Room: If the room is heavily shaded, you can decrease the capacity by 10%.
• Kitchen: If the AC is for a kitchen, add 4,000 BTU/hr to account for heat from cooking appliances.

Basic Rule of Thumb (The Area Method)

A simple way to estimate is: Area (sq ft) x 25 = Required BTU/hr

Then divide by 12,000 (since 1 Ton = 12,000 BTU/hr).

Example: Room size: 15 ft x 12 ft = 180 sq ft. 180 x 25 = 4,500 BTU/hr. This seems low because 25 is a very conservative multiplier for basic cooling. A more robust multiplier in hot climates is 60-70 BTU per sq ft.

Hot Climate Calculation: 180 sq ft x 60 = 10,800 BTU/hr. 10,800 / 12,000 = 0.9 Ton. -> A 1.0 Ton AC would be suitable. If it's a top floor or sunny room, go for 1.5 Ton to be safe.

Summary Table

Note: These are estimates. For precise requirements, consult with an HVAC professional.