The social-class dimension of energy consumption has been rather neglected relative to other theoretical approaches to energy use, despite its potential deployment in energy policies. This paper aims at investigating energy policy-related inequalities across social classes with respect to three dimensions highlighted by environmental-justice theories: income distribution, procedures producing unequal distributional outcomes, and cultural and political recognition of vulnerable and marginalised social groups. These inequalities can be exacerbated or reduced by social diffusion processes, both vertical and horizontal. These processes include policy instruments intending to lower energy consumption in the residential sector. To empirically ground the analysis, two countries with contrasting patterns of income inequalities, Portugal and Belgium, are compared on the basis of qualitative data collected in 2009-2011. We discuss the relevance of integrating the social diffusion dimension in energy policies and propose several policy instruments to do so. One of our main contribution is to argue that both vertical and horizontal diffusion across social classes, if adequately translated into policy instruments, can boost the uptake of residential energy retrofits and other energy saving practices. (C) 2015 Elsevier Ltd. All rights reserved.