|Due to the daunting prospect of harmful climate change, policymakers around the world have been pushing for energetic retrofits in the real estate markets to reduce their carbon footprint. Despite the common ground and high ambitions, we still face a vast gap between the modern technical possibilities of energy efficiency and the slow adoption of these opportunities in and around our homes. In this paper, we review the main causes of this energy efficiency gap, ranging from the behavioral economics of hyperbolic discounting to the non-monetary expenses of refurbishments. Moreover, we introduce the RentalCAL tool, which is designed to close at least parts of this gap across Europe. The RentalCAL tool helps landlords of residential dwellings to assess the financial consequences of energy efficiency improvements, including investment levels, rent repayment, and dwellings price appreciation. We discuss the RentalCAL tool configuration, and demonstrate how different elements can help to alleviate the barriers to residential energy efficiency.