The paper is devoted to the development of a method for calculating the thermal stability of external enclosing structures with heat-conducting inclusions. Based on the analysis of existing methods and methodologies for solving the problem of heat resistance of enclosing structures with heat-conducting inclusions, the solution of the one-dimensional problem of heat resistance was established to be characteristic for all these works. One of the possible methods for determining the amplitude of temperature fluctuations on the inner surface of the enclosing structure with heat-conducting inclusions is the simulation of non-stationary temperature conditions in software systems. However, this solution causes great difficulties, since it transfers the indicated calculation from engineering to scientific and, therefore, cannot be recommended for direct practical application. The second solution to this problem is to use the convergence coefficient α, which can be obtained empirically. By choosing the value of the coefficient α, one can take into account the effect of a heat-conducting inclusion on the weighted average value of the surface temperature depending on the design of the fence. The paper presents values of the convergence coefficient α for six most common cases of heat-conducting inclusions in enclosing structures. When analyzing the design solutions of external enclosing structures, the features of the influence of heat-conducting inclusions on the averaged amplitude of oscillations on the inner surface were revealed. In the schemes with outer edge or through location of the heat-conducting inclusion, there is a slight influence of the amplitude of the oscillation of the heat-conducting inclusion on the averaged amplitude over the surface of the structure. The greatest degree of influence is exerted by the scheme with the through arrangement of heat-conducting inclusion. On the basis of the comparative analysis, it was found that when constructing harmonics of average temperature fluctuations on the inner surface, preference is given to the methodology with the convergence coefficient.