The purpose of this study is to investigate how secondary homes in Sweden can be more energy efficient, and the goal is to guide owners of cottageswith low energy efficiency. The study has compared 2 reference cottages in four different locations. Cottage 1 has poor windows and direct electric heat for space heating, and Cottage 2 has improved windows and a heat pump. Computer software was used during the study. Bim Energy was used to compare the energy use for cottages 1 and 2, calculating pay-off time for the investment and finding the energy use with additional insulation. The Swedish building code energy calculation was used to calculate the timeconstant for the cottages with different thicknesses of additional insulation. PVGIS was used to find the PV system output.The result shows that cottage 2 has an energy reduction of 58-61%. Thetime constant is 27-39 hours, depending on how much additional insulationis added. The PV system does not cover all energy use, but during summer, surplus energy is produced. Conclusions that can be drawn, by changing the heating system and improving windows reduce the energy use, the timeconstant will increase with thicker additional insulation, and a PV systemcan help to reduce the energy use.