Washington · NOAA station KSEA
Heating with a mini-split in Seattle, WA
The short answer
In Seattle, a median ENERGY STAR cold-climate mini-split heating a 24,000 BTU/h design load should cost about $1,127 a year: $142 more than natural gas (90% efficient), and 64% less than electric resistance. The 99% design temperature is 30°F, so capacity at 5°F rarely decides anything here.
The winter you are actually buying for
This is Seattle's average year of hourly temperatures from 2015 through 2024 (87,599 readings at Seattle-Tacoma International Airport, 99.9% of all hours). The dashed line is the 99% design temperature: only 1% of hours are colder.
What it costs, by fuel
Mini-split modeled as a median certified cold-climate unit sized to cover the load at 30°F. Seasonal efficiency in Seattle's weather: COP 2.81. In 68 hours a year the load exceeds capacity and the estimate adds electric backup.
Three house sizes
| Design load | Heat pump | Gas | Oil | Propane | Resistance | Seasonal COP | Systems that cover it |
|---|---|---|---|---|---|---|---|
| 12,000 BTU/h | $563 | $493 | $1,104 | $1,112 | $1,584 | 2.81 | 11,057 of 14,941 |
| 24,000 BTU/h | $1,127 | $985 | $2,208 | $2,224 | $3,168 | 2.81 | 5,688 of 14,941 |
| 36,000 BTU/h | $1,690 | $1,478 | $3,311 | $3,337 | $4,752 | 2.81 | 3,003 of 14,941 |
The last column counts ENERGY STAR cold-climate systems whose published 5°F and 47°F capacities, joined by a straight line, still reach the design load at Seattle's 30°F. How sizing works.
Not a quote. Real bills depend on insulation, thermostat habits, installation and your own Manual J. Use this to decide whether a heat pump is worth pricing, then get two local quotes.
Questions people ask
Will a mini-split work in Seattle in winter?
Yes, if it is a cold-climate model. Seattle's 99% design temperature from 2015–2024 hourly data is 30°F, and the lowest hour recorded was 15°F. The median ENERGY STAR cold-climate unit keeps 88% of its 47°F heating capacity at 5°F. Hours per year at or below 5°F in Seattle: 0.
Is a heat pump cheaper than natural gas in Seattle?
At a 24,000 BTU/h design load, we estimate $1,127 a year with a median cold-climate mini-split versus $985 for natural gas at 90% efficiency, using 14.20¢/kWh electricity and 2024 Washington fuel prices. That is $142 more than natural gas.
How big a mini-split do I need in Seattle?
Size to your home's heat loss at 30°F, not to square feet. For a 24,000 BTU/h load, a unit shaped like the median certified system needs about 25,190 BTU/h of 47°F capacity. 5,688 of the 14,941 certified systems cover that load at 30°F.