Heating Degree-Day Map: Your Winter Heat Budget in kWh and Cords

A house does not have a heating bill so much as a heat loss, multiplied by a winter. Heating degree days measure the winter half of that: how far below comfortable the outside air sat, and for how long. One number, summed day by day, and it is the climate figure a wood pile, a propane tank or a heat pump actually responds to.

Below is the annual figure for the 48 contiguous US states and 30 European countries on both official bases, mapped and tabulated, then the arithmetic that turns it into a winter fuel order.

What a Degree Day Counts

Take one day’s mean outdoor temperature. Subtract it from a fixed base temperature. If the answer is positive, that is the day’s heating degree days. Sum the year and you have the annual figure.

The base is not a comfort setting. It stands for the outdoor temperature at which a building stops needing heat, because body heat, cooking, lighting and daylight already cover the loss. Older housing stock balanced out near 65°F, which is where the American convention comes from.

The two authorities on this page do not count the same way, and that matters more than the unit does.

	NOAA, United States	Eurostat, Europe
Base temperature	65°F (18.3°C)	18°C (64.4°F)
Days counted	Every day the mean falls below the base	Only days whose mean is 15°C or lower
Daily mean	Midpoint of the day’s high and low	Daily mean air temperature on a 25 km grid
Combined by	Population weight within each state, 2010 Census	Grid cells averaged up to NUTS-3 regions
Unit	Degree Fahrenheit days	Degree Celsius days

The unit conversion is simple arithmetic: one degree Fahrenheit day is five ninths of a degree Celsius day. Both columns are printed for every row in the table below, so nobody has to do it.

The counting rule is the part that does not convert. A day averaging 16°C scores 4.2 degree Fahrenheit days under the American rule — 2.3 in Celsius terms — and exactly zero under the European one, because 16 sits above the 15°C gate. Across a mild Atlantic autumn those days add up.

So a European figure carried into Fahrenheit reads slightly colder than it would have if the American rule had been applied to the same weather. Finland’s 5,557 degree Celsius days become 10,003 in Fahrenheit terms, ahead of North Dakota’s 9,184, and that gap is real rather than an artifact.

From Degree Days to Kilowatt-Hours

Steady-state heat loss is one line of physics: watts out equals the shell’s heat loss coefficient times the temperature difference across it. Hold that over a whole season and the temperature difference, integrated, is the degree-day total.

Winter heat (kWh) = UA (W/K) × 24 × HDD (°C·days) ÷ 1,000

UA is the whole-house heat loss coefficient: walls, roof, floor, glass and air leakage added together. Nobody knows theirs without a survey, so it is normally estimated from floor area and a shell factor.

Building shell	Btu/hr per sq ft per °F	W per m² per K	What it looks like
Old and leaky, little insulation	0.30	1.70	Solid wall or uninsulated frame, single glazing, drafty
Average existing house	0.20	1.14	Loft insulation, double glazing, ordinary air sealing
Well insulated and tight	0.12	0.68	Deep retrofit or a build to a current energy code
Very tight modern build	0.07	0.40	Thick continuous insulation, triple glazing, blower-door tested

The same four bands drive the winter-wood calculator on the firewood BTU chart, so the two pages agree with each other by construction.

Those two houses are the same house, and the two climates are within 2% of each other. Ohio and Germany run almost identical winters once both are put on one scale, which is the whole reason for printing both bases side by side.

One warning about the bottom band. The degree-day method gives no credit for sunshine through the windows or the heat thrown off by people, cooking and appliances. In a leaky house those gains are lost almost as fast as they appear; in a very tight one they cover a real share of the winter, so the method reads high exactly where the building is best. Treat the 0.07 row as a ceiling rather than a forecast.

Both Continents on One Scale

Both maps are shaded on one scale: annual heating degree days on the 18°C base, 1991–2020. US state figures are the NOAA 65°F totals converted at five ninths, so the two continents can be read against each other on sight.

United States Europe

under 1,0001,000 – 2,0002,000 – 3,0003,000 – 4,0004,000 – 5,0005,000 and overno figure in this dataset

The American map is a north-to-south gradient bent by altitude. New Mexico, at 4,462 on the 65°F base, carries a third more degree days than North Carolina, at 3,359, while sitting slightly further south; the difference is elevation.

Europe’s map is bent by the ocean instead. Ireland, at 2,785 on the 18°C base, is milder than Slovakia, at 3,327, while sitting further north. The Atlantic keeps the western edge of the continent several hundred degree days warmer than the same latitude inland.

Your Winter in Cords, Pellets and Propane

Pick a place, set the floor area and the shell, and this converts the degree-day figure into a fuel order. Heat delivered to the room, then divided by what each fuel carries and by how much of that heat the appliance actually releases into the house.

Run it through the off-grid house calculator before assuming a battery bank can carry it, and check the panel side against the peak sun hours atlas, where December is the month that sizes the array.

Every State and Country

The 48 contiguous US states first, then 30 European countries, alphabetically within each group. Tap any column heading to re-sort, including across both groups at once.

The two degree-day columns are the same number in different units. The winter heat and cord columns are for one fixed reference house — 150 square meters, or 1,615 square feet, of average existing construction — so the columns rank climates rather than describing any particular building.

Download the full table as CSV →

The CSV adds the 2015–2024 mean in both units and the reference house’s steres, pellet kilograms and propane in gallons and liters.

How These Numbers Were Made

US rows come from NOAA’s nClimDiv statewide heating degree-day series, element 25 of the statewide monthly file published by the National Centers for Environmental Information. Monthly values were summed by calendar year and averaged over 1991–2020, then again over 2015–2024.

The series is built from 5 km grid estimates interpolated from Global Historical Climatology Network station data, and its degree-day totals are population-weighted within each state on 2010 Census weights. NOAA calls these operational monitoring values, which can differ slightly from its official degree-day publications.

The file carries no rows for Alaska or Hawaii, and the District of Columbia is not one of its statewide units. All three are left out rather than estimated from a product built a different way.

European rows come from the Eurostat annual series nrg_chdd_a, indicator HDD, averaged over the same two windows. Eurostat interpolates roughly 3,000 station records onto a 25 km grid, then averages those cells up to NUTS-3 regions and on to countries.

Its rule is stated exactly: if the day’s mean air temperature is at or below 15°C, add 18°C minus that mean; otherwise add nothing. Norway, Switzerland and the United Kingdom appear in the series alongside the member countries and are included here.

The reference house is 150 square meters with a shell factor of 0.20 Btu per hour per square foot per °F, which is 1.14 watts per square meter per kelvin, giving a UA of 170 watts per kelvin. Winter heat is that UA times 24 hours times the degree-day figure, with no credit for solar or internal gains and no allowance for domestic hot water.

Fuel conversions use the Energy Information Administration’s published heat contents: 20 million Btu per cord of wood, 91,452 Btu per gallon of propane, 3,412 Btu per kilowatt-hour. A stere is one stacked cubic meter; a cord is 128 cubic feet, so one cord is 3.62 steres.

Pellets are taken at 4.8 kWh per kilogram net, the 17.3 GJ per tonne the UK Government’s 2025 greenhouse gas conversion-factor methodology lists for pellets at 10% moisture. Wetter pellets carry less.

The four appliance efficiencies are assumptions, set at seasonal averages rather than peak bench figures, and each is printed beside the output it drives. A different stove or furnace moves the fuel quantity in direct proportion.

Verified September 2026. NOAA nClimDiv statewide file climdiv-hddcst-v1.0.0-20260806 retrieved 2 September 2026. Eurostat nrg_chdd_a retrieved the same day, dataset last updated 8 May 2026. Both series are revised on their own schedules; the retrieval date is the date to quote.

Common Questions

Sources: NOAA National Centers for Environmental Information, nClimDiv statewide monthly heating degree days, file climdiv-hddcst-v1.0.0-20260806, and the accompanying statewide format documentation. Eurostat, Cooling and heating degree days by country, annual data (nrg_chdd_a), and its reference metadata for the calculation rule. US Energy Information Administration, Energy Explained: British thermal units, for the cord, propane and kilowatt-hour heat contents. UK Government, 2025 greenhouse gas reporting conversion factors, methodology paper Table 51, for the net calorific value of wood pellets. University of Maryland Extension FS926 and University of Arkansas FSA1091 for the cord convention used across this site.