For one room. To size a heat pump for a whole house, ask your installer for a Manual J load calculation: insulation, windows and climate change the answer.
How the size is calculated
- Area: length × width of the room.
- Base capacity: the cooling capacity for that area in the ENERGY STAR sizing chart, which assumes an 8-foot ceiling (ENERGY STAR).
- ENERGY STAR adjustments:
- Heavily shaded room: 10% less.
- Very sunny room: 10% more.
- More than two people regularly in the room: 600 BTU more for each extra person.
- Kitchen: 4,000 BTU more.
Tons = BTU ÷ 12,000.
Choosing the unit
Mini-splits come in fixed sizes, often in steps of a few thousand BTU. Choose the closest size at or above the result. A unit that is much too large cools the room quickly but turns on and off often and removes less humidity. If the ceiling is higher than 8 feet, you may need more capacity.
The chart is for cooling. In cold climates, check the unit's heating capacity at your winter design temperature in the manufacturer's data.