Energy efficiency by means of reduction in wasteful energy consumption is a growing policy priority for many countries. Innovative systems should be designed to continuously monitor a smart city environment and provide all stakeholders the tools to improve energy efficiency. This paper presents the EDEN platform, designed to collect and analyze thermal energy consumption of residential and public building heating systems. EDEN is being deployed in a major Italian city and collects energy consumption measurements through an extensive smart metering grid involving thousands of buildings. EDEN also collects and analyzes indoor climate conditions, and user feedbacks, such as their thermal comfort perception, by means of an ad-hoc social network. Collected data are further enriched with temporal and spatial information at different abstraction levels and meteorological data available as an open source data set. Several technical Key Performance Indicators (KPIs) have been defined to inform users on their building thermal energy consumption, while user-friendly KPIs present energy savings or over-consumptions in an informative fashion.