Energy analysis of complex buildings is usually carried out by process analysis. The results are indices of the direct consumption by final energy carriers. This analysis, however, is not complete because the final energy carriers are generated in a system of interconnected production and transport processes, where energy is also used. The sum of the direct energy use, the energy used in intermediate stages and in transport is termed cumulative energy consumption. The analysis of cumulative energy consumption may concern either one single final energy carrier (e.g. electricity) or the global primary energy consumption. The theory of cumulative energy consumption belongs to the class of system methods. This paper applies one system method, input-output analysis, to compare different systems of supplying energy to buildings. The linear mathematical model of annual energy balance of a complex case-study building has been formulated. The paper describes the application of such a linear mathematical model for calculating the coefficients of cumulative energy consumption in buildings as well as for evaluating the effects of energy rationalisation systems and strategies. (C) 2005 Elsevier B.V. All rights reserved.