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 2021

IIIIIIIVVVIVIIVIIIIXXXIXIIYear
Maarianhamina550569471395215000145
Vantaa6727045533691160016207
Helsinki636661527346116000171
Pori6606655193971670013211
Turku6556565233811510013203
Tampere6967155644031760019230
Lahti6937225773871610020227
Lappeenranta7097646063971580020244
Jyväskylä7547686234262020036277
Vaasa6967165594252350021226
Kuopio7728126334262130028267
Joensuu7928366524322230044284
Kajaani8388686654512380064301
Oulu8268246324372430051267
Sodankylä9718606904853641635120333
Ivalo9298416884934071674135325
Updated 1.10.2021 10:34.

Monthly average temperature 2021 (°C)

IIIIIIIVVVIVIIVIIIIXXXIXII
Maarianhamina-0.7-3.31.83.88.516.519.515.511.1
Vantaa-4.7-8.1-0.94.510.419.220.915.49.5
Helsinki-3.5-6.60.05.010.319.321.415.910.4
Pori-4.3-6.70.33.89.517.919.515.29.5
Turku-4.1-6.40.14.19.918.420.315.29.7
Tampere-5.4-8.5-1.23.69.718.820.014.68.7
Lahti-5.3-8.8-1.64.110.119.721.215.09.0
Lappeenranta-5.9-10.3-2.63.810.119.821.214.98.5
Jyväskylä-7.3-10.4-3.12.89.218.619.614.07.5
Vaasa-5.4-8.6-1.02.88.016.519.214.49.0
Kuopio-7.9-12.0-3.42.89.418.920.614.98.0
Joensuu-8.5-12.9-4.02.69.319.020.314.67.4
Kajaani-10.0-14.0-4.52.08.417.318.813.46.8
Oulu-9.6-12.4-3.42.48.016.619.314.18.0
Sodankylä-14.3-13.7-5.20.84.515.216.911.85.9
Ivalo-13.0-13.0-5.20.63.514.515.311.76.2
Updated 1.10.2021 10:34.

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.