Cleanroom production is energy- and CO2-intensive. Determining energy consumption and energy-saving measures is worthwhile. For the necessary overview, a holistic optimisation approach should be pursued that includes all trades in and around the cleanroom. The case study of the energy audit in a cleanroom production facility shows the importance of consistent energy data, process understanding and prioritisation of the main consumers. Last but not least, the importance of specific energy consumption for proper analysis and interpretation. The topic of funding for energy-saving measures is discussed in the outlook section.