The Candy Factory area is located at Brynäs district, and its history is known as Gävle's most important industrial area in the 1870’s. The area is under construction and plans to tie Gävle Strand with Brynäs and make the area more attractive. In the Candy Factory area in Gävle there is a building, Läkerol building that is owned by AB Gavlegårdarna, and is a part the areas renovation process. It’s exterior must be preserved but must be made more energy efficient since the building is to be used as a residential building and other activities. It is part of a cultural environment, such as national interests. The retention of its characters is particularly important, making changes to the building more complex.

The starting point for this study was to investigate the effects of energy efficiency methods and costs with a focus on windows in view of conservation needs of the Läkerol building. In the implementation, characteristics of the building have been assessed along with literature research, previous research, books studied in support of the work and energy balances and cost calculations for window changes have been made.

The results for this study shows what is most profitable among different efficiency methods and how different building envelope components leak heat. The windows cause great thermal losses and cost savings can be reduced by choosing the efficiency measure window with extra glass with low investment cost compared to brand new windows.