Mini Split BTU Sizing Calculator
Determine the exact cooling and heating capacity required for your space.
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Recommended Capacity
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How to Calculate BTU for a Mini Split
Choosing the right size for a ductless mini-split system is critical for both comfort and energy efficiency. A unit that is too small will run constantly without ever reaching the desired temperature, while an oversized unit will "short cycle," turning on and off rapidly, which leads to poor dehumidification and premature wear on the compressor.
The standard rule of thumb is approximately 20 BTUs per square foot of living space. However, this base calculation doesn't account for variables like ceiling height, insulation quality, or localized heat sources like kitchen appliances.
Key Factors Influencing BTU Sizing
- Square Footage: The primary driver of capacity. Multiply length by width.
- Ceiling Height: Standard calculations assume 8-foot ceilings. If your ceilings are 10 feet or higher, you need to increase capacity by roughly 20-25%.
- Insulation: Well-insulated homes retain conditioned air longer, requiring fewer BTUs. Older homes with drafty windows require a significant boost in power.
- Occupancy: Humans generate heat. If more than two people regularly occupy a room, add 600 BTUs per additional person.
- Kitchens: Cooking appliances generate massive amounts of heat. Always add at least 4,000 BTUs if the indoor unit is located in a kitchen area.
Common Mini Split Sizes
Mini splits typically come in standardized sizes. Once you have your calculated BTU, you should round up to the nearest available unit size:
| BTU Rating | Approx. Area (Sq. Ft.) |
|---|---|
| 9,000 BTU | 300 – 450 sq. ft. |
| 12,000 BTU (1 Ton) | 450 – 600 sq. ft. |
| 18,000 BTU (1.5 Tons) | 600 – 1,000 sq. ft. |
| 24,000 BTU (2 Tons) | 1,000 – 1,200 sq. ft. |
The Importance of Inverter Technology
Most modern mini splits use inverter-driven compressors. Unlike traditional HVAC units that are either "on" or "off," inverters can slow down or speed up to match the exact cooling load. This means if your room needs 10,500 BTUs but you buy a 12,000 BTU unit, the inverter will simply run at a lower speed, saving electricity and maintaining a perfectly steady temperature.