Reducing overall household energy consumption through the application of information and communication technologies (ICT) can play an important role in the transformation towards sustainable consumption patterns, e.g. through the optimisation of energy-consuming processes. The challenge in the environmental assessment of ICT applications is to also consider their use-specific environmental effects, as these can be decisive for overall results. Using the example of smart heating, we therefore analyse the environmental performance of a sample of 375 smart home systems (SHS) in Germany and show how the life cycle assessment (LCA) can be extended to include various use-specific effects such as choice of products and individuals' behaviour when using the product. In an interdisciplinary study design, we combine life cycle modelling and behavioural science to systematically include use-specific parameters into the modelling, and to interweave these results with user characteristics such as sociodemographics and user motivation. Our results are heterogenous: For the impact category Climate Change (GWP) we find that having smart heating can lead to large savings in particular cases. On average, however, smart heating does not lead to significant benefits for GWP, but neither does it represent an additional burden. For Metal Depletion Potential (MDP), we find that smart heating is always an additional burden, as heating optimisation has almost no reduction potential for MDP. Our results have a wide range due to large differences in use patterns in the sample. Depending on the impact category, both number of devices of the SHS as well as heating temperature are decisive. Regression analysis of our assessment results with user characteristics shows that differences in MDP and GWP of SHS size can be explained by income, and, in addition, differences in GWP of net heating energy savings can be explained by user motivation. Our results thus underline that the standard scenarios for user behaviour assumed in LCA modelling should be well justified. Future interdisciplinary research should further explore the links between use-specific approaches in LCA and users' environmental behaviour and motivation.