This standard gives a simplified calculation method for assessment of the heat use and energy needed for space heating of a residential building, or a part of it, which will be referred to as "the building". This method includes the calculation of: 1) the heat losses of the building when heated to constant temperature; 2) the annual heat needed to maintain the specified set-point temperatures in the building; 3) the annual energy required by the heating system of the building for space heating. The building may have several zones with different set-point temperatures.