This study presents a methodology to measure the impact of solar heating systems, on reducing peak demand and on avoided emissions, when applied in low-income housing projects. To this end, a real-time monitoring system was implemented over a year in five clusters representative of a heterogeneous socioeconomic context in new housing subsidized with solar water heating system through the national program "My House, My Life". The results showed an expressive contribution of the system in reducing the maximum peak demand, obtaining, on average, a 64% reduction in relation to the electric showerhead, predominantly used in the country. The cumulative energy savings of 577 kWh per year resulted in an average of 250 kgCO(2) avoided per housing unit. The extrapolation of the data to 224,000 units already delivered by the national program would result in an economy of 56,089 tCO(2) per year. This study demonstrates the importance of measurement as a strategic tool in public policies for energy efficiency and in the estimation of emissions associated with greenhouse gases. The solar heating system positions itself as an important energy efficiency policy for Brazil, which minimizes the demand for thermoelectric plants during peak hours and postpones investments with new power generation plants. (C) 2018 Elsevier Ltd. All rights reserved.