A computerized system that carries out both energy efficiency diagnoses and cost/benefit analyses for energy efficiency measures is described. The Mexican agency, FIPATERM, provides soft financing for residential customers who participate in demand side management (DSM) programmes. Current FIPATERM programmes are: thermal insulation, substitution of the current airconditioning system by an efficient one, infiltration reduction, levelled annual payment plan, and interruption of the airconditioning equipment during peak demand hours. The residential customers who want to participate in one or several energy efficiency programmes, must agree to an energy efficiency diagnosis. Then, from both, house construction characterization and a customer equipment operation survey, the simulator allows some of the most profitable DSM measures to be identified.