An indirect control technique using a single-zone space model is presented. The practice of adjusting temperature of heat supply medium inversely to outdoor air temperature (basic open-loop approach) was replaced with a flux control mechanism and facilitated with Takahashi algorithm1. In thismodel a coupling Laplace equation was applied with a noncapacitive nodal net of conductance and the hemisphere surface envelope concept in long-wave radiation calculations. In order to reduce the system’s order and make it ready for direct use with DDC techniques used nowadays without requiring an additional math apparatus, the transient responses of the output vector were subjected to approximation instead. The ability of working in a closed control loop was demonstrated using data obtained from middle-long-term temperature measurement at ordinary single-zone spaces during the heating season.