Within the emerging discipline of Energy Informatics people are researching, developing and applying information and communication technologies, energy engineering and computer science to address energy challenges. In this paper we discuss the challenge of advancing energy informatics to enable assessable improvements of energy performance in buildings. This challenge follows a long-standing goal within the built environment to develop processes that enable predictable outcomes. Implementing this goal in the research framework of energy informatics creates a need for establishing a new underlying assumption, which states that the impact of energy informatics solutions should be assessable. This assumption applies to particular building contexts and when solutions act simultaneously. Research based on this assumption will enable new sound processes for the built environment facilitating informed decision for adding intelligent solutions to buildings compared to only favoring passive building improvements.