A housing association in Ludvika owns an apartment building built 1942 with a heating system based on district heating. The housing association is interested in reducing their annual energy cost, which corresponds to reducing their energy consumption. The yearly energy consumption for the building at the moment is about 40 % above the average for Swedish apartment buildings. This report investigates the possibilities of reducing the total energy consumption for the building, in a profitable way, and at the same time meeting the governmental targets for 2050 and the maximum specific energy demand for new buildings presented by the building regulation. The method used in this report was to conduct simulations of models of the building where proposals in terms of reducing the use of heat were evaluated. The proposals were related to the ventilation system, the building envelope, and solar power installations. The simulations returned results of many proposals that could reduce the energy consumption, but just a few turned out to be financially viable. Installing an exhaust air heat pump in combination with solar panels for heat supply and solar cells for electricity was found to be the most viable solution. A combination of these three proposals was calculated to reduce the yearly heat consumption with 188 MWh and the total energy consumption by 50 %, which meets the 2050 target. The specific energy consumption of the building per square meter of heated area is 97 kWh, which means that the maximum specific energy demand of 110 kWh is met.