3 Head Mini Split: Sizing Each Zone and What It Costs
Updated · By the Roof to Footing editors
A 3 head mini split is a ductless heat pump system with one outdoor unit feeding three indoor units, or "heads," each in its own room with its own thermostat. It's a common way to heat and cool an addition, a finished attic, an older house without ducts, or three rooms that the central system doesn't serve well. HomeGuide puts a 3-zone system at about $7,000 to $11,000 installed; other cost guides quote wider ranges.
How sizing works
You size each head for its room, then pick an outdoor unit that can run all three.
| Room | Rough head size |
|---|---|
| Bedroom or office, 150 to 300 sq ft | 6,000 to 9,000 BTU |
| Larger bedroom or small living area, 300 to 450 sq ft | 9,000 to 12,000 BTU |
| Living room, kitchen or open area, 450 to 700 sq ft | 12,000 to 18,000 BTU |
Those ranges are rough. Sun exposure, ceiling height, insulation and climate change the numbers, so ask for a room-by-room load calculation.
Tri-zone outdoor units commonly come in about 24,000 to 36,000 BTU (2 to 3 tons). Most manufacturers allow the indoor heads to add up to somewhat more than the outdoor unit's rating, because not every room needs full output at once. Each maker publishes allowed combinations; stay inside them.
Line sets and layout
Each head connects to the outdoor unit with its own refrigerant line set, drain line and control wire, run through a 3-inch hole in the wall.
- Every system has a maximum length per head and a maximum total length. Long runs reduce capacity.
- Heads need a path for condensate to drain by gravity or a small pump.
- Line set covers on the outside wall protect the lines and look neater.
Plan the outdoor unit location for short runs, good airflow and clearance from snow.
Multi-zone vs. separate single-zone units
| One 3-zone system | Three single-zone systems | |
|---|---|---|
| Outdoor units | One | Three |
| Upfront cost | Usually lower | Usually higher |
| Efficiency | Good; some loss at part load | Often higher per room |
| If the outdoor unit fails | All three rooms lose heat and cooling | Only one room affected |
| Wall space outside | Less | More |
Pros and cons
| Pros | Cons |
|---|---|
| No ductwork needed | Wall-mounted heads are visible |
| Each room has its own temperature | Filters on each head need regular cleaning |
| High efficiency, good low-temperature heating with cold-climate models | Multi-zone systems cost more per BTU than single-zone in some cases |
| Quiet indoor units | Needs a qualified installer; refrigerant work requires certification |
Cost factors
- Head type: wall-mounted is cheapest; ceiling cassette and concealed-duct heads cost more.
- Electrical: a dedicated circuit and disconnect, sometimes a panel upgrade.
- Line set length and wall penetrations.
- Brand and efficiency (SEER2 and HSPF2 ratings).
For a whole-house ducted option, compare with a 2 ton heat pump. Mini splits are also a popular choice for manufactured homes; see AC for a mobile home.