This paper presents a new method for selecting the energy reference year, which may be used for many applications, such as the energy performance of buildings, the simulation of active or passive solar energy systems, HVAC system performance or indoor climate analyses.The EN ISO 15927-4 method was modified by using monthly dependent weighting factors for the main climatic parameters in the calculation of heating and cooling energy demand in buildings. We used data from the cold Finnish boreal climate to demonstrate the method. In a cold boreal climate, during the summer temperature and solar radiation have a similar influence on heating and cooling energy demand, whereas air humidity and wind speed have a minor effect. The principle for determining the weighting factors and modified method for the selection of the energy reference year can also be used for other climatic zones. The weighting factors determined in this study can be used for other countries in a cold climatic area. (C) 2011 Elsevier B.V. All rights reserved.