Guide
How many mini split zones you need
A head for every closed room, each sized to that room.
Short answer
One zone, meaning one indoor head, for every room you want heated or cooled that can be closed off, because a head only reaches the space it blows into. A three-bedroom house in a mixed climate usually needs 5 heads, one each for the bedrooms, living room and kitchen, on an outdoor unit of about 30,000 BTU.
A worked example: three bedrooms, mixed climate
| Room | Area | Cooling load | Head |
|---|---|---|---|
| Living room, 16 × 20 ft | 320 sq ft | 7,400 BTU | 9,000 BTU |
| Kitchen and dining, 14 × 16 ft | 224 sq ft | 9,180 BTU | 12,000 BTU |
| Main bedroom, 14 × 16 ft | 224 sq ft | 5,180 BTU | 6,000 BTU |
| Bedroom 2, 12 × 12 ft | 144 sq ft | 3,330 BTU | 6,000 BTU |
| Bedroom 3, 10 × 12 ft | 120 sq ft | 2,775 BTU | 6,000 BTU |
| Total | 1,032 sq ft | 27,865 BTU | 39,000 BTU |
The heads add up to more than the load, 39,000 BTU against 27,865, because each one is rounded up to the next size sold. The outdoor unit is sized to the real load, not to the sum of the heads: here about 30,000 BTU. Multi-zone outdoor units are built to run heads whose nameplates add up to more than their own rating, because the rooms rarely all call at once; each manufacturer publishes the combinations it allows.
Rules for deciding the zones
- A door means a zone. Bedrooms and offices that are closed at night or during the day need their own head.
- Open-plan space can share one. A living, dining and kitchen area with no walls between can be one zone if one head is sized for the whole area.
- Skip rooms you do not condition. Bathrooms, halls and closets are usually left to the air that drifts in from the rooms around them.
- Check the maximum per outdoor unit. Most residential multi-zone units take two to five heads; a larger house may need two outdoor units.
Why not one big head in the hall?
A mini split has no ducts. A head in the hallway conditions the hallway and whatever rooms are open to it, and the far corners of closed bedrooms stay several degrees off. For a whole-house result from one unit, a ducted mini split or a conventional ducted heat pump is the right tool, not a larger wall head.