How to Size a Mini Split Correctly
[Image of Mini Split air conditioner mounted on wall]Sizing a ductless mini-split isn't just about guessing. Getting the right size is crucial for efficiency and comfort. This calculator uses the standard rule of thumb (approximately 20-30 BTUs per square foot) adjusted for environmental factors.
Why does sizing matter?
- Undersized (Too Small): The unit will run continuously, failing to reach the desired temperature, driving up electricity bills, and wearing out the compressor early.
- Oversized (Too Big): The unit will "short cycle," meaning it turns on and off rapidly. This prevents the unit from properly dehumidifying the room, leaving the air feeling clammy and sticky, even if it's cold.
Factors That Change Your BTU Needs
Ceiling Height
Standard calculations assume 8ft ceilings. If you have vaulted or cathedral ceilings, you have more air volume to cool, requiring roughly 20% more power.
Insulation & Windows
Old windows or poor insulation allow heat to enter faster. We add a buffer (15-20%) for poorly insulated rooms to ensure the unit keeps up.
Sunlight
A south-facing room with big windows gets significant solar heat gain. Shaded rooms require less cooling power.
Kitchens
Kitchens generate their own heat from ovens, stoves, and fridges. It is standard practice to add ~4,000 BTUs to the load for a kitchen.
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