Mini-Split Sizing Calculator
A load sketch for splitting BTU across heads — not Manual J. Click any i for detail.
Zones
Conditioned sq ft
i
Area
All rooms the system should serve. |
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|---|---|
BTU per sq ft
i
Climate
Hot ~25, mixed ~22, mild ~18. |
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Heads / zones
i
Heads
Indoor units. BTU is split equally for this sketch. |
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Insulation
i
Insulation
Scales the load. Poor older walls vs tight new construction. |
How to use this calculator
- Enter the total area to condition.
- Raise the factor in a hot climate.
- Set how many indoor heads you want.
- Compare tons (12,000 BTU) to equipment catalogs.
Results explained
Load = sq ft × factor × insulation multiplier. Headline rounds to the nearest 1,000 BTU. Multi-zone jobs are rarely even splits in the real world.
Quick reference: ductless sizes
Common single-zone outdoor units are 9, 12, 18, and 24k BTU.
| Item | Detail |
|---|---|
| 9k BTU | ~0.75 ton |
| 12k BTU | 1.0 ton |
| 18k BTU | 1.5 ton |
| 24k BTU | 2.0 ton |
Line-set length, elevation, and inverter range matter as much as BTU.
How the estimate is built
BTU = area × factor × {1.15 poor | 1.0 average | 0.9 good}. Tons = BTU / 12,000.
Example scenario
350 sq ft × 22 × 1.0 = 7,700 BTU, rounds to a 9k-class single zone on many charts.
FAQ
One outdoor, two heads?
Add the rooms’ loads; don’t just split a living-room number in half without measuring both.
Heat vs cool?
This is a cooling-oriented sketch. Cold-climate heat pumps are sized on heating load.
Install cost?
See heat pump / HVAC cost calculators.