Heat Roadmap Europe 3 is from work package 2 of the STRATEGO project (http://stratego-project.eu/). It quantifies the impact of implementing various energy efficiency measures in the heating and cooling sectors of five EU Member States: Czech Republic, Croatia, Italy, Romania, and the United Kingdom. These countries vary considerably in terms of population, climate, resources, and energy supply, so the key results, conclusions, and recommendations presented in this report can inform national energy policy across all of Europe. The results from this study indicate that a total investment of approximately €1.1 trillion in energy efficiency measures across all five of these countries, between 2010 and 2050, will save enough fuel to reduce the costs of their energy systems. After considering both the initial investment and the resulting savings, the total annual cost of the heating, cooling, and electricity sectors is reduced by an average of ~15% in each country. These initial investments are primarily required in heat savings for the buildings, district heating in urban areas, and electric heat pumps in rural areas. In essence, energy efficiency measures in the heating sector will enable EU Member States to simultaneously reduce energy demand, imported fossil fuels, carbon dioxide emissions, and the cost of the heating, cooling, and electricity sectors.