How the math works
Condensus mathCooling kWh = cooling BTU × load × cooling hours ÷ (SEER2 × 1,000). Heating kWh = heating BTU × load × heating hours ÷ (HSPF2 × 1,000). SEER2 and HSPF2 are the maker's seasonal ratings: BTU of cooling or heating delivered per watt-hour used, measured under the 2023 DOE test.
Condensus mathThe last row shows the same heat from electric resistance heaters (baseboards, space heaters), which deliver 3,412 BTU per kWh, so you can see what a heat pump saves when it replaces them.
LimitsSeasonal ratings are averages; a cold winter, a high thermostat setting, long line sets or a poor installation raise real use. Systems that don't state SEER2 are not listed, and heating cost is skipped when HSPF2 isn't stated.
Questions
What is a good SEER2 for a mini-split?
The federal minimum for new split heat pumps is 14.3 SEER2 in most of the country. Many ductless systems are rated around 18 to 22 SEER2, and each point higher cuts cooling energy by roughly 5% at the same output.
Is a mini-split cheaper to run than a space heater?
Usually much cheaper. A heat pump with an HSPF2 of 8 to 9 delivers roughly 2.3 to 2.6 times as much heat per kWh as a resistance heater over a season, though the advantage shrinks in very cold weather.