Guide
Heating and cooling degree-days, explained
Degree-days are the simplest way to compare how much heating or cooling a climate needs. They are why the same house needs four times as much heat in Minnesota as in Texas, and they sit inside the heating and efficiency calculators on this site.
What a degree-day is
A degree-day measures how far a day's average temperature is from 65 °F, the point below which most homes need heat.
- Heating degree-days (HDD). If a day averages 40 °F (say a high of 50 and a low of 30), it counts 65 − 40 = 25 heating degree-days. A day at 65 °F or warmer counts zero.
- Cooling degree-days (CDD). If a day averages 80 °F, it counts 80 − 65 = 15 cooling degree-days. A day at 65 °F or cooler counts zero.
Add the days up over a year and you get one number for heating and one for cooling. Twice the heating degree-days means, to a first approximation, twice the heat a house loses over the winter, and so twice the fuel.
Why 65 °F? Inside a heated house, people, appliances, lights and sunlight add heat of their own. At an outdoor average around 65 °F, those gains roughly cover the losses, so the heating system only has to make up the difference below that point. It is a convention, not a law of physics, but it works well enough that utilities and engineers have used it for decades.
Degree-days by state
| # | State | Heating degree-days | Cooling degree-days | Climate zone |
|---|---|---|---|---|
| 1 | Alaska | 10,000 | 0 | 7 |
| 2 | North Dakota | 9,000 | 500 | 7 |
| 3 | Minnesota | 8,000 | 600 | 6 |
| 4 | Montana | 7,600 | 400 | 6 |
| 5 | Vermont | 7,600 | 300 | 6 |
| 6 | Maine | 7,400 | 300 | 6 |
| 7 | South Dakota | 7,400 | 800 | 6 |
| 8 | Wisconsin | 7,400 | 600 | 6 |
| 9 | Wyoming | 7,400 | 300 | 6 |
| 10 | New Hampshire | 7,300 | 400 | 6 |
| 11 | Iowa | 6,700 | 900 | 5 |
| 12 | Michigan | 6,600 | 600 | 5 |
| 13 | Illinois | 6,200 | 900 | 5 |
| 14 | Nebraska | 6,200 | 1,100 | 5 |
| 15 | Colorado | 6,000 | 700 | 5 |
| 16 | Connecticut | 5,800 | 700 | 5 |
| 17 | Idaho | 5,800 | 700 | 5 |
| 18 | Massachusetts | 5,800 | 600 | 5 |
| 19 | Ohio | 5,700 | 900 | 5 |
| 20 | Rhode Island | 5,700 | 600 | 5 |
| 21 | Utah | 5,700 | 900 | 5 |
| 22 | Pennsylvania | 5,600 | 900 | 5 |
| 23 | Indiana | 5,500 | 1,000 | 5 |
| 24 | New York | 5,500 | 800 | 5 |
| 25 | New Jersey | 5,000 | 1,000 | 4 |
| 26 | Missouri | 4,900 | 1,400 | 4 |
| 27 | Kansas | 4,800 | 1,500 | 4 |
| 28 | Washington | 4,800 | 200 | 4 |
| 29 | West Virginia | 4,800 | 900 | 5 |
| 30 | Delaware | 4,600 | 1,200 | 4 |
| 31 | Maryland | 4,600 | 1,300 | 4 |
| 32 | Oregon | 4,600 | 300 | 4 |
| 33 | Kentucky | 4,400 | 1,300 | 4 |
| 34 | District of Columbia | 4,200 | 1,500 | 4 |
| 35 | New Mexico | 4,000 | 1,400 | 4 |
| 36 | Virginia | 4,000 | 1,400 | 4 |
| 37 | Tennessee | 3,600 | 1,600 | 4 |
| 38 | Oklahoma | 3,500 | 2,100 | 3 |
| 39 | North Carolina | 3,400 | 1,600 | 3 |
| 40 | Arkansas | 3,200 | 2,000 | 3 |
| 41 | Nevada | 3,000 | 2,500 | 3 |
| 42 | Georgia | 2,800 | 1,800 | 3 |
| 43 | Alabama | 2,600 | 2,000 | 3 |
| 44 | South Carolina | 2,600 | 2,100 | 3 |
| 45 | California | 2,500 | 900 | 3 |
| 46 | Mississippi | 2,300 | 2,400 | 3 |
| 47 | Texas | 2,000 | 2,900 | 2 |
| 48 | Louisiana | 1,800 | 2,800 | 2 |
| 49 | Arizona | 1,400 | 3,800 | 2 |
| 50 | Florida | 700 | 3,300 | 2 |
| 51 | Hawaii | 0 | 4,400 | 1 |
| US average | 4,500 | 1,300 | 4 |
Source: EIA, August 2026; natural gas EIA 2025 annual average; degree-days NOAA 1991–2020 normals. Full dataset on the data page.
These are NOAA Climate Prediction Center normals for 1991–2020, base 65 °F, weighted by population. Weighting by population means each state's figure leans toward where most people live: California's number reflects its populous coastal and valley areas more than its mountains. The climate zone column is the zone our calculators use for heat pump efficiency and cooling hours.
The extremes are wide. Alaska has 10,000 heating degree-days and almost no cooling; Hawaii has 4,400 cooling degree-days and no heating. Most of the continental US sits between about 2,000 and 8,000 HDD, with the US average at 4,500 HDD and 1,300 CDD.
How degree-days scale heating costs
Our heating calculators estimate a year's heat loss as:
heated area × insulation factor × HDD × 24 hours
The insulation factor is 0.25 BTU per hour per square foot per °F for a tight, well-insulated house, 0.35 for an average one and 0.50 for a drafty one. For a 2,000 sq ft house with average insulation, that is 16,800 BTU per heating degree-day.
Worked example, the same house in three places:
| Texas | US average | Minnesota | |
|---|---|---|---|
| Heating degree-days | 2,000 | 4,500 | 8,000 |
| Heat needed per year | 33.6 MMBtu | 75.6 MMBtu | 134.4 MMBtu |
| Gas furnace, 92% efficient | 365 therms | 822 therms | 1,461 therms |
| Cost at the state's gas price | $682.92 | $1,216.12 | $1,548.55 |
| Heat pump, seasonal COP | 3.4 | 2.8 | 2.3 |
| Heat pump electricity | 2,896 kWh | 7,913 kWh | 17,126 kWh |
| Cost at the state's electricity rate | $460.75 | $1,437.00 | $2,945.67 |
Gas: $1.87, $1.48 and $1.06 per therm. Electricity: 15.9¢/kWh, 18.2¢/kWh and 17.2¢/kWh.
The heat needed scales exactly with HDD: Minnesota needs four times what Texas does. The fuel cost doesn't, because prices differ by state. And the heat pump's electricity grows faster than the HDD, because heat pumps lose efficiency in colder climates. Our calculators use a seasonal COP that falls from 3.6 in the warmest zone to 1.8 in the coldest; below about 25 °F, real units can lose capacity as well, which we don't model.
Degree-days also explain the calendar. On average, January brings about 20% of a year's heating degree-days and December 21%, while June to August together bring almost none. Our space heater and electric blanket calculators spread their yearly cost using that pattern.
How degree-days scale cooling costs
Cooling degree-days work the same way in the other direction, and the gap between states is just as wide: Florida has 3,300 CDD, Washington 200. About 69% of the year's cooling degree-days fall from June through August, with July the peak.
Cooling is harder to predict from degree-days alone, for two reasons. Humid air has to be dried as well as cooled, and that moisture load doesn't show up in the temperature. And sun through windows and on the roof can drive the AC on a day that isn't especially hot. So for central air, our SEER2 savings calculator uses full-load cooling hours by climate zone instead: 2,000 hours a year in zone 2, 1,100 in zone 4 and 600 in zone 6.
For a 3-ton system at SEER2 14, which draws about 2,570 W, that gives about 5,143 kWh a year in Florida (zone 2), 2,829 kWh in an average US climate and 1,543 kWh in Minnesota: $770.94, $513.75 and $265.40 at each place's rate. Cooling degree-days do feed directly into our attic insulation and window replacement calculators, where the saving on cooling scales with CDD just as the heating saving scales with HDD.
What degree-days don't capture
Degree-days compare climates; they don't describe your house. A few things move your real costs:
- Insulation and air sealing. The difference between a tight and a drafty house is a factor of two in our model, as big as moving several hundred miles north.
- Your thermostat. Keeping the house at 68 °F instead of 72 °F lowers the effective balance point. A thermostat setback at night or while you're out cuts the hours the system runs.
- Your specific location. A state figure is a population-weighted average. Mountain towns, high plains and coastal cities in the same state can differ a lot. For an exact local number, look up the weather station nearest you.
- One year versus normal. These are 30-year normals. A mild winter or a hot summer will be above or below them.
Calculators that use degree-days
- Heat pump vs furnace: yearly heating cost of each at your state's HDD and prices.
- Gas vs electric heat: resistance heat, a gas furnace and a heat pump compared.
- Attic insulation savings: heating and cooling savings scaled by HDD and CDD.
- Smart thermostat savings: heating and cooling cost by climate zone.
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