This paper presents results of a three-year research project focused on the emplacement of Home Energy Management Systems (HEMS) in a living lab setting with seven households. The HEMS used in this study allowed householders to monitor energy consumption both in real-time and in retrospective on the TV and on mobile devices. Contrasting with existing research focused on how technology persuades people to consume less energy, our study uses a grounded approach to analyze HEMS emplacement. As an important result, we present here the issue of 'energy literacy'. Our study reveals that, by using HEMS, participants became increasingly literate in understanding domestic electricity consumption. We discuss the role HEMS played in that process and how the acquired literacy changed energy consumption patterns. We conclude that literacy in energy consumption has value on its own and explain how eco feedback system designs can benefit from this understanding.