How many zones do you need?
Count the areas you want independently controlled, not the rooms you have. This gives you a head count and a rough capacity for each, so you can read a ductless quote and know whether it makes sense.
Four questions about the home
Typical head capacity by room
Nominal indoor head capacity in BTU/h, for a home built between 1960 and 1990. Older homes need more, newer homes less. Heads come in fixed sizes, so a real system rounds to what the manufacturer makes.
| Area | Floor area | Rough head size |
|---|---|---|
| Bedroom | 120 sq ft | 6,000 |
| Large bedroom or office | 180 sq ft | 6,000 |
| Small living area | 250 sq ft | 9,000 |
| Medium living area | 400 sq ft | 12,000 |
| Large or open plan | 600 sq ft | 15,000 – 18,000 |
| Very large open plan | 800 sq ft | 24,000 |
The rules this follows
- One head per independently controlled area, not per room. Air does not go through closed doors or round corners.
- Open-plan living, kitchen and dining is usually one zone, however large it is on the floor plan.
- Bedrooms are a lifestyle question. Some households need every one conditioned; some need none.
- Bedrooms are assumed at about 120 sq ft, and other separate areas at about 180 sq ft.
- Heads are sized from the same load-per-square-foot bands as the whole-home sizing tool.
Where this stops being useful
Past about four heads, a ductless multi-zone starts losing to a ducted system on both cost and comfort — and the minimum-output problem gets worse, because a big outdoor unit serving one small calling bedroom cannot turn down far enough.
If this tool tells you five or six zones, that is a signal to price a ducted system as well rather than a reason to buy six heads.
Read the multi-zone trap before you commit to a head count. It is the part of the decision that quotes rarely explain.
Want this checked properly?
Tell us which rooms are uncomfortable now and which doors stay shut. That conversation decides the system more than the floor plan does.