Lately, the topic of sustainability is booming, and one of the main concerns isto make buildings more energy efficient. For this purpose, energy audit is agreat tool that helps to realise the weaknesses of each building and helps toimprove them. This topic has been used and studied in recent years, and themain objective of this study is to perform a complete energy audit of aresidential house in mid-Sweden, considering its age. With all the data obtainedfrom the house and the bills, calculations are made by hand to see the weakpoints of the house and improve them. The main heat losses of the building arethe transmission losses. The final suggestions are to change the windows of thebuilding and try to avoid thermal bridges. These two measures have high initialinvestment costs, and their economic profitability depends on them. However,from the energetic point of view both measures are interesting. It is alsorecommended not to use electric radiators, as they are much less energyefficient. The installation of solar panels is studied, with satisfactory results,reaching the conclusion that they are highly recommended for this type ofhouse. Even though Sweden is not the country with more sun, the solar PVpanels work efficiently in cold countries.