Maine · NOAA station KPWM
Heating with a mini-split in Portland, ME
The short answer
In Portland, a median ENERGY STAR cold-climate mini-split heating a 24,000 BTU/h design load should cost about $2,224 a year: $899 more than natural gas (90% efficient), and 61% less than electric resistance. The 99% design temperature is 7°F, so capacity at 5°F rarely decides anything here.
The winter you are actually buying for
This is Portland's average year of hourly temperatures from 2015 through 2024 (87,609 readings at Portland International Jetport Ap, 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 7°F. Seasonal efficiency in Portland's weather: COP 2.56. In 54 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 | $1,112 | $662 | $865 | $1,249 | $2,847 | 2.56 | 10,960 of 14,941 |
| 24,000 BTU/h | $2,224 | $1,325 | $1,730 | $2,498 | $5,694 | 2.56 | 5,436 of 14,941 |
| 36,000 BTU/h | $3,337 | $1,987 | $2,596 | $3,747 | $8,540 | 2.56 | 2,682 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 Portland's 7°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 Portland in winter?
Yes, if it is a cold-climate model. Portland's 99% design temperature from 2015–2024 hourly data is 7°F, and the lowest hour recorded was -16°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 Portland: 54.
Is a heat pump cheaper than natural gas in Portland?
At a 24,000 BTU/h design load, we estimate $2,224 a year with a median cold-climate mini-split versus $1,325 for natural gas at 90% efficiency, using 29.60¢/kWh electricity and 2024 Maine fuel prices. That is $899 more than natural gas.
How big a mini-split do I need in Portland?
Size to your home's heat loss at 7°F, not to square feet. For a 24,000 BTU/h load, a unit shaped like the median certified system needs about 27,001 BTU/h of 47°F capacity. 5,436 of the 14,941 certified systems cover that load at 7°F.