In the context of increasing transmission capacities during the last years, the investigation of thermal effects, especially for gas-insulated systems, is required. Higher operating currents decrease the gas density in the vicinity of the heated conductor significantly. Hence, the insulation strength of the system is reduced. Dimensioning for different load scenarios requires a comprehensive knowledge of the temperature influence on the insulation performance of AC and DC installations. This paper introduces an algorithm to predict the temperature-dependent breakdown voltage utilizing the streamer criterion and proves its functionality by experimental investigations. Necessary input parameters, like the electrical field strength and the gas density, can be gained from numerical calculations. The insulation strength of the investigated arrangement at a conductor temperature of 100 °C is decreased by (10 … 15) % in comparison to a conductor temperature of 20 °C. The accordance between measurement and calculation proves the quality of the model.