The research project HERMES seeks to analyze two underlying limits on energy efficiency research. Not only recent research on energy efficiency assume that households are perfectly informed, and that information is perfectly exploited, but it is often assumed that households are homogenous in their preferences. Our project seek to analyze the behavioral use of information by households, as well as to allow for households’ preference heterogeneity for energy performance. A particular attention will be given to policies aimed at households in a vulnerable condition or suffering from fuel poverty. To deal with our research program, the project uses a combination of state-of-the art econometrics and simulation techniques, with an array of datasets (ENL2013, PERVAL, BIEN, DPE, PHEBUS).