The EU-funded PreMa project investigates the potential for a preheating stage to reduce the electrical energy requirement and CO\(_2\) emissions produced, during the production of high-carbon ferromanganese in a submerged arc furnace. A pilot-scale campaign will be conducted at MINTEK in South Africa to demonstrate the potential effect of preheating on furnace operation. For the pilot-scale campaign, the design of the process flowsheet and sizing of the furnace and ancillary equipment were based on predictive mass and energy balance calculations. FactSage thermodynamic software and Microsoft Excel were utilised. The paper reports on the method applied and results obtained.