Sizing is the one decision you can't fix after install day. A unit sized right runs quietly for years; one sized wrong cycles hard, costs more to run, and wears out early. The math is simple, and it takes about two minutes.
Start with the base rule
A room with normal ceilings and decent insulation, in a moderate climate, needs about 20 BTU per square foot. Mini splits are labeled in thousands of BTU per hour: a "12K" unit moves 12,000 BTU/hr.
| Space | Square feet | Typical size |
|---|---|---|
| Bedroom, office | up to 450 | 9K |
| Large bedroom, studio | 450–600 | 12K |
| Open living area | 600–900 | 18K |
| Large open plan | 900–1,200 | 24K |
| Very large space | 1,200–1,500 | 30K–36K |
| Whole house, several rooms | 1,500+ | Multi-zone or ducted |
NG single-zone systems run from 9K to 36K across the BLU+ Single Zone and SAJA Single Zone series.
When to size up one step
- High ceilings. Anything over 9 feet adds volume the unit has to condition.
- Strong sun or hot climate. South-facing rooms with big windows, or summers like Phoenix and central Texas.
- Poor insulation. Older homes, garages, converted attics, sunrooms.
- Heat-producing rooms. Kitchens and home gyms carry more load than a bedroom.
When to size down one step
Only if all of these apply: new or recently weatherized construction, a north-facing room with little sun, a moderate coastal climate, and light use.
Why bigger is not better
An oversized unit reaches the set temperature too fast, shuts off, and starts again minutes later. That short cycling never runs long enough to pull humidity out of the air, so the room ends up cold and clammy. It also wears the compressor faster. If you're between two sizes and none of the size-up conditions apply, take the smaller one.
Voltage, quickly
Most 9K and some 12K units run on standard 115V household circuits. Everything 18K and up, and every multi-zone outdoor unit, needs a dedicated 208/230V circuit. Each product page lists the voltage in the title and the spec table. If you're not sure what your panel supports, ask an electrician before you order.
The short version
- 20 BTU per square foot is the starting point, not the final answer.
- Adjust one step for ceilings, sun, insulation, and how the room is used.
- Never oversize on purpose. Short cycling is the most common self-inflicted problem.
- Over about 1,500 square feet or several rooms, look at multi-zone or ducted instead.
Not sure which way to go? Browse the catalogue or call (877) 811-1251. English or Spanish, Monday through Friday, 8 to 5 Pacific.
