Degree-days and the climate of each département
Degree-days measure how much heating is needed. The site worked them out for each département from Météo-France daily records.
The heating degree-day (DJU in French) is the standard tool for measuring a place’s heating need. For each day, take the gap between 18 °C and the average outdoor temperature, when it is lower; add them up over the year. A place with 2,000 degree-days needs roughly twice as much heating as one with 1,000, for the same house. The site worked out these figures from the daily data published as open data by Météo-France, for the station nearest each département’s main town, averaged over the ten years 2015 to 2024, and then for 2025 alone. The gaps are wide: 933 in Haute-Corse (Bastia_Sapc), 2,736 in Lozère (Mende-Ville). These figures feed the site’s whole chain of calculation: heat needed, heat pump consumption, saving and payback. The climate zone H1, H2 or H3, which sets the CEE bonus factor, comes from a different text, the order of 26 October 2010, and does not exactly follow degree-days.
My département’s climate
Degree days per year (2015-2024)
2,071 DJU
| Year 2025 | 2,003 DJU |
| Climate zone | H2 |
| Reference station | Rennes-St Jacques (36 m) |
| 3 coldest days | 0.1 °C |
Checked by Radif Partners · Editorial policy · Method and sources
The mildest and coldest départements
| Mildest | HDD | Zone | Coldest | HDD | Zone |
|---|---|---|---|---|---|
| Haute-Corse (2B) | 933 | H3 | Lozère (48) | 2,736 | H2 |
| Var (83) | 1,100 | H3 | Ardennes (08) | 2,731 | H1 |
| Corse-du-Sud (2A) | 1,126 | H3 | Haute-Marne (52) | 2,721 | H1 |
| Pyrénées-Orientales (66) | 1,212 | H3 | Vosges (88) | 2,697 | H1 |
| Alpes-Maritimes (06) | 1,370 | H3 | Haute-Loire (43) | 2,674 | H1 |
| Bouches-du-Rhône (13) | 1,370 | H3 | Territoire de Belfort (90) | 2,645 | H1 |
| Hérault (34) | 1,373 | H3 | Meuse (55) | 2,577 | H1 |
| Gard (30) | 1,418 | H3 | Moselle (57) | 2,527 | H1 |
The full ranking of all 96 départements, with the saving a heat pump brings there, is on the heat pump by département page.
My département’s climate
Degree days per year (2015-2024)
2,071 DJU
| Year 2025 | 2,003 DJU |
| Climate zone | H2 |
| Reference station | Rennes-St Jacques (36 m) |
| 3 coldest days | 0.1 °C |
2025 compared with the average
| Département | 2015-2024 average | Year 2025 | Gap |
|---|---|---|---|
| Alpes-Maritimes | 1,370 | 1,279 | -7 % |
| Bouches-du-Rhône | 1,370 | 1,240 | -9 % |
| Gironde | 1,491 | 1,358 | -9 % |
| Ille-et-Vilaine | 2,071 | 2,003 | -3 % |
| Loire-Atlantique | 1,937 | 1,880 | -3 % |
| Rhône | 2,058 | 1,982 | -4 % |
| Paris | 1,835 | 1,816 | -1 % |
| Nord | 2,359 | 2,292 | -3 % |
| Bas-Rhin | 2,267 | 2,305 | 2 % |
| Puy-de-Dôme | 2,166 | 2,128 | -2 % |
A year milder than average lowers the heating bill, and so the saving a heat pump brings. The calculator uses the ten-year average, more representative of a unit’s lifetime.
How the site calculates degree-days
For each département, the site takes the Météo-France station nearest the prefecture with complete records, from the daily files published on meteo.data.gouv.fr. For each day it averages the minimum and maximum temperature, takes the gap to 18 °C when positive, and adds up over the calendar year. Years with too many missing days are discarded. Details are on the method page, and the calculation script is published with the site’s code.
Climate zones
Zone H1 covers the North, the East, Île-de-France, the Centre and part of the Massif Central and Alps; zone H3 the Mediterranean coast and Corsica; zone H2 everything else. The factor applied to the CEE bonus is 1.2 in H1, 1.0 in H2 and 0.7 in H3.