The aim of a massive reduction of CO2-emissions results in a move away from fossil fuels. In the hot strip production of steel, almost exclusively gas-fired furnaces are currently used due to the lower energy costs. On the contrary, it is imperative to convert existing fossil heated processes to CO2-free (green) technologies in the context of the energy-transition. Obvious alternatives are electrical heating or hydrogen combustion, both strongly dependent on the specific electricity generation mix that determines the CO2-emissions. In this case study, different process heat generation options for continuous reheating furnaces in steel hot rolling mills are discussed by a quantitative approach. A state-of-the-art reheating furnace fired with natural gas is used as reference case, while electrical heating, hydrogen-air heating and hydrogen-oxygen heating are the alternatives investigated. The energy balances, the primary energy consumption and the resulting CO2-emissions are compared for the three countries of France, Poland and Germany with regard to the country-specific electricity generation mix. Additionally, the possible development until 2050 is analysed. The results show the high impact of continuous reheating furnaces in steel hot rolling mills on the total CO2-emissions of downstream steel processing. Furthermore, the massive increase in electrical energy consumption of the whole steel production process is highlighted. Each investigated alternative shows a significant potential to save CO2-emissions, depending on the country specific electricity generation mix and the future expansion of renewable energy sources. An increase in H2-production efficiency will both lead to a lower primary energy consumption and lower CO2-emissions for reheating furnaces. •Reheating furnaces have a high impact on CO2-emissions in downstream steel processing.•Primary energy consumption changes based on process heat generation alternative.•Alternative technologies show big potential to emit less CO2 than state-of-the-art.•Potential savings depend on technology and country-specific electricity generation mix.•CO2-emissions could be further reduced by increased H2-production efficiency.