More than 50% of the existing housing stock in Spain is over 50 years old and was built according to the construction standards of its time, and nowadays shows poor energy performance compared to the current standards, meaning higher energy consumption due to the lack of energy retrofitting interventions (no insulation materials, low window performance, high infiltration and thermal bridges). The link between homes and health has been well established by the scientific community and research results illustrate how the condition of existing buildings is one of the most decisive influences on population's health. However, the role of energy retrofitting in improving health of occupants has still to be thoroughly and comprehensively documented. Normally, benefits of energy retrofitting are calculated only in terms of energy savings and associated economic savings. Long pay-back periods and high investment make energy retrofitting not attractive enough to many homeowners. Highlighting the health benefits may help to improve the rate at which the housing stock undergoes energy retrofitting. The aim of this research is to estimate the effect that energy efficiency improvements made to vulnerable housing has on the health of the occupants and to assess the potential economic savings for the Spanish healthcare system.