Low‐emissivity (low‐E) window films are designed to improve the thermal comfort andenergy performance of buildings. These films can be applied to different glazing systems withouthaving to change the whole window. This makes it possible to apply films to windows in old andhistorical buildings for which preservation regulations often require that windows should remainunchanged. This research aims to investigate the impacts of low‐E window films on the energyperformance and thermal comfort of a three‐story historical stone building in the cold climate ofSweden using the simulation software “IDA ICE”. On‐site measurements were taken to acquirethermal and optical properties of the windows. This research shows that the application of the lowemissivitywindow film on the outward‐facing surface of the inner pane of the double‐glazedwindows helped to reduce heat loss through the windows in winter and unwanted heat gains insummer by almost 36% and 35%, respectively. This resulted in a 6% reduction in the building’sannual energy consumption for heating purposes and a reduction in the percentage of totaloccupant hours with thermal dissatisfaction from 14% (without the film) to 11% (with the film).However, the relatively high price of the films and low price of district heating results in a ratherlong payback period of around 30 years. Thus, the films seem scarcely attractive from a purelyeconomic viewpoint, but may be warranted for energy/environmental and thermal comfort reasons.