1. BTU capacity - the size
Listed as BTU/h (e.g., 12,000 BTU) or in "tons" (1 ton = 12,000 BTU). This is the unit's cooling/heating output - match it to your room, not the other way around. Bigger isn't better; an oversized unit short-cycles. Size first with the size chart and sizing guide.
2. SEER2 - cooling efficiency
The seasonal cooling efficiency rating; higher is better. Modern mini splits run from the high teens into the mid-20s and beyond. A higher SEER2 means lower cooling bills. It's the headline number for cooling - explained fully in SEER2 and HSPF2 explained.
3. HSPF2 - heating efficiency
The heating counterpart to SEER2; higher is better (typically ~8-11). If you'll heat with the unit, this matters as much as SEER2. A high HSPF2 signals efficient winter operation.
4. The low-temperature rating - cold-weather capability
The number that separates a mild-climate unit from a cold-climate one. Look for an operating temperature range or a rated-capacity-at-low-temp figure (e.g., "100% capacity at 5F" or "operates to -13F"). Two cautions: an operating floor (how cold it still runs) isn't the same as a rated-capacity point (how cold it delivers full heat), and if you need winter heat, match this to your climate - see cold-weather performance.
5. Voltage and electrical (MCA / MOP)
- Voltage: 115V (smaller units, standard circuit) or 230V (most 12k+, needs a dedicated 230V circuit).
- MCA (Minimum Circuit Ampacity) and MOP (Maximum Overcurrent Protection): these size the wire and breaker. Your electrician uses them - see electrical requirements.
6. Sound level (dB)
Given for the indoor head (often a range, low to high fan speed) and sometimes the outdoor unit. Lower is quieter. Indoor heads can run in the high teens to ~30s dB; the outdoor unit is louder (see outdoor unit noise). If quiet matters, compare the low-speed indoor dB.
What to skim past (at first)
Refrigerant type (relevant for future-proofing - R-32 vs R-454B), line-set diameters and max length, dimensions and weight, and warranty terms all matter after you've matched capacity, efficiency, climate, electrical, and noise. Don't let them distract from the six that decide the shortlist.
The bottom line
Read six numbers - capacity, SEER2, HSPF2, low-temp rating, voltage/MCA-MOP, and dB - and you can compare any two mini splits on what actually matters. Everything else is detail for after you've narrowed it down. Put the shortlist together in the product finder, which lets you filter on exactly these.
FAQ
What numbers matter most on a mini split spec sheet? BTU capacity (size), SEER2 (cooling efficiency), HSPF2 (heating efficiency), the low-temperature rating (cold-weather capability), voltage and MCA/MOP (electrical), and dB (noise).
What is a good SEER2 rating for a mini split? Higher is better; modern units range from the high teens into the mid-20s and above. A higher SEER2 means lower cooling costs - weigh it against price and your climate.
What does the low-temperature rating tell me? How well the unit heats in the cold. Check whether it's an operating floor (how cold it still runs) or a rated-capacity point (how cold it delivers full heat), and match it to your winter.
What are MCA and MOP on a mini split? Minimum Circuit Ampacity and Maximum Overcurrent Protection - the electrical figures your electrician uses to size the wire and breaker for the unit's dedicated circuit.