The paper describes the use of the theory of tolerances in thermal network models that are built as electric circuits. A principle of the method and main equations are given. A calculation of new values of model parameters is based on the assessment of relative sensitivities of model elements. The method is explained in a case study where thermal comfort is analysed in a designed office building in summer. Tolerances make possible to quickly find a new parameter value for the desired air temperature decrease. The limitation of the method is in using differential sensitivities that can be used for relatively small changes of parameter values.