Heating degree days

Heating degree day describes the demand for energy needed to heat buildings.

Notice! Heating degree day values for the summer months in the normal period 1981-2010 were found to be erroneous. These values have since been fixed on January 20th 2014. In the annual values the correction is under one percent in the south and in the north the correction is even smaller.

Heating degree days 2020

IIIIIIIVVVIVIIVIIIIXXXIXIIYear
Maarianhamina414440450368254
Vantaa467478473367194
Helsinki434452452351180
Pori447479482384226
Turku455477479387228
Tampere498520505408227
Lahti500509496406199
Lappeenranta526528510422211
Jyväskylä542557551459255
Vaasa496527523428257
Kuopio564568550471240
Joensuu582582555482246
Kajaani619628605514286
Oulu593607584496269
Sodankylä820750702565347
Ivalo855734684563363
Updated 2.6.2020 7:36.

Monthly average temperature 2020 (°C)

IIIIIIIVVVIVIIVIIIIXXXIXII
Maarianhamina3.71.82.54.87.9
Vantaa1.90.51.74.59.5
Helsinki3.01.42.45.19.6
Pori2.60.51.44.28.3
Turku2.30.51.54.18.2
Tampere0.9-0.90.73.48.5
Lahti0.9-0.61.03.59.1
Lappeenranta0.0-1.20.63.09.1
Jyväskylä-0.5-2.2-0.81.77.6
Vaasa1.0-1.20.12.77.3
Kuopio-1.2-2.6-0.71.38.2
Joensuu-1.8-3.1-0.90.97.9
Kajaani-3.0-4.7-2.5-0.16.5
Oulu-2.1-3.9-1.80.56.8
Sodankylä-9.4-8.9-5.6-1.85.0
Ivalo-10.6-8.3-5.0-1.84.5
Updated 2.6.2020 7:36.

Heating degree days during the normal period 1981-2010

IIIIIIIVVVIVIIVIIIIXXXIXIIYear
Maarianhamina592567551406216343171353084325423803
Vantaa682640586376146162211583484976254097
Helsinki647612566383153111121253164645883878
Pori677633585389181263251713524976224161
Turku663625575377161192181493384866084021
Tampere724675612400176285341923825296674424
Lahti726677610395159204311913835286684392
Lappeenranta759699621403165225281843865466924510
Jyväskylä7857216464402064010562274145697184832
Vaasa719666619424214295351923775266634469
Kuopio812741653445198317381944005717354825
Joensuu8267536654562163910472154165897524984
Kajaani8647776954792515717752454416187855304
Oulu824742677465249479552244235937495057
Sodankylä946838760548345106491363165237228916180
Ivalo923819755557377146691473185237228756231
Updated 20.1.2014 8:13.

The normal period of the heating degree days has been changed to the averages of the climatological normal period of 1981-2010 and the coefficients has been calculated to be equivalent to the new normal period. Old reference values can be ordered from the Climate Service Centre.

What is a heating degree day?

With the help of a heating degree day, the consumption of heating energy is standardized in order to compare the energy consumption of a building in different months or years as well as comparing buildings in different municipalities. The heating degree day is used in estimating the need for heating a building because the energy consumption of a building is almost linear to the difference between the outside and inside temperature.

The heating degree day is calculated monthly for 16 cities of comparison. Those cities are Mariehamn, Vantaa, Helsinki-Kaisaniemi, Pori, Turku, Tampere-Pirkkala, Lahti, Lappeenranta, Jyväskylä, Vaasa, Kuopio, Joensuu, Kajaani, Oulu, Sodankylä, and Ivalo. If ordered, heating degree days can also be calculated for other areas.

How is the heating degree day calculated?

The heating degree day is calculated by adding up the differences of the daily indoor and outside temperatures of the whole month. The most commonly used heating degree day is S17, which is calculated by adding up the difference between the presumed indoor temperature +17°C and the daily average outside temperature. The heating degree day of a month is the sum of the daily heating degree days of the month and the heating degree day of a year is the sum of the monthly heating degree days of the year. The average heating degree day of the normal period 1981-2010 is used as the comparative value.

Days when the average temperature is above +10°C in the spring and above +12°C in the autumn are not taken into account in calculating the heating degree day. It is presumed that the heating is turned on or off when the outside temperature goes daily above or below the above-mentioned limits. If the temperature observations are missing, the daily average temperatures are interpolated.