What you need to know
- Capacity in Btu per hour. Mini splits are sold by size, such as 9,000, 12,000, 18,000 or 24,000 Btu per hour. It is on the label of the outdoor unit and in the listing.
- Efficiency rating. Usually SEER2 for cooling. Mini splits are often listed with a higher rating than other air conditioners; use the number on your unit.
- Hours of use. The hours a day it works at full capacity. A mini split slows down to hold the temperature, so a unit running all day may count as fewer hours at full capacity.
- Price per kWh. The rate on your bill, or the state average the calculator starts from.
The formula
Power in kilowatts = capacity ÷ rating ÷ 1,000. Cost per hour = power × price per kWh. Multiply by the hours to get the cost per day.
A 12,000 Btu per hour unit with a rating of 20 draws 0.6 kW. At the U.S. average price of 16.5 cents per kWh (2024), that is $0.10 per hour. For 8 hours a day it is $0.79 a day, and over a 120-day cooling season it is $95. The size, rating and hours are assumptions for this example.
Cost of a day by size and rating
The table shows the cost of 8 hours at full capacity at 16.5 cents per kWh. The sizes and ratings are assumed for illustration. Your own rating and rate change every figure in proportion.
| Size (Btu/h) | Rating 20 | Rating 25 |
|---|---|---|
| 9,000 | $0.59 | $0.47 |
| 12,000 | $0.79 | $0.63 |
| 18,000 | $1.19 | $0.95 |
| 24,000 | $1.58 | $1.27 |
Why a mini split can cost less than the formula says
The formula describes the unit at full capacity. A mini split with a variable-speed compressor slows down once the room reaches the set temperature and draws less power. If you enter the hours it is on, the result can be too high. If you enter the hours it would take at full capacity, it is closer. Past bills are the best check.
Heating with a mini split
Many mini splits are heat pumps and also heat. The cooling rating above does not apply to heating, which has its own rating (HSPF2). To compare heating with gas, use the heat pump vs gas furnace calculator.