Three energy models of the apartment building with different level of detail were studied. The study was carried out to assess the possibility of simplifying the model of the late design stage or using the model of the early design stage to perform energy calculations. The maximum divergence of the calculation results of the simplified and detailed models did not exceed 10%. On average, the divergence of the results was equal to 8% in the case of the calculations of the concept and detailed models, and the divergence of the results was equal to 5% in the case of the calculations of the moderately simplified and detailed models respectively. In the case of energy calculations at the early design stage it can be considered a rather small value. The use of the simplified building model for energy calculations can be recommended. The use of the detailed model was considered to be irrational and can be recommended only in the case of the existence of compelling reasons.