Mini Split Size Calculator
A ductless mini split is sized by how much heat a room gains. This gives a rough cooling figure in BTU per hour from the floor area. It is a starting point, not a full load calculation.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The floor area is converted to square feet and multiplied by a rule-of-thumb figure in BTU per hour for each square foot. The right figure depends on climate, sun exposure, ceiling height and how many people use the room.
This is an estimate only. It is not a full room-by-room load calculation, which looks at windows, insulation, air leaks and more.
Worked example
A room of 300 ft² at a rule of thumb of 20 BTU per hour per square foot comes to about 6,000 BTU/h of cooling.
Questions
What is a full load calculation?
It is a detailed room-by-room calculation done by a trained person or specialist software. It is the better basis for choosing equipment size.
Does this allow for ceiling height?
No. Taller rooms hold more air and gain heat differently, so the figure may need raising. The rule of thumb is one number for the whole floor.
Why is the BTU figure so large?
BTU per hour measures how fast heat moves, and a room gains thousands of BTU per hour, so the number runs large.
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