Thermal simulations are an important means to predict the energy performance of buildings or groups of buildings or even whole cities. In particular with long term simulations the performance is vital for achieving good results in an acceptable amount of time. Resistance-capacitance models are well suited for simulating multi-zone models or running long-term simulations or a combination of both. Automatic model reduction even of resistance-capacitance models may be needed in order to improve the peformance of building simulations. They aim at accurate energy calculation or accurate calculation of temperature profiles. Several ways of automatable model reduction are outlined in detail in the work at hand.