This study calculated the total useful energy demand of residential buildings in Geneva for both the current heat mix and four prospective scenarios for 2035. A lifecycle assessment was conducted to evaluate the impacts of supplying residential buildings with one year of heat in the present and future scenarios, using the current heat mix as a baseline for comparison. The results showed that the future scenarios would decrease the total useful heat demand by maximum 20% compared to the baseline (2.2TWh). Every future scenario except BAU would decrease global warming impacts by 40-50%. The EE+ scenario is the only scenario that would significantly reduce the impacts on fine particulate matter formation (-59%) and global warming (-44%) without increasing the impacts on mineral resource scarcity and water consumption. However, these results are sensitive to the quantity of heat delivered. Furthermore, no energy source for the heat mixes had the lowest impacts in every impact category. Finally, significant impacts were identified over the lifecycle of renewable energy sources besides the use phase, notably during the production phase of wood, heat pumps and solar thermal systems.