ESDU 78028 is one of a group of five dealing with this topic. It provides a method of estimating the thermal resistance by breaking down the assembly into its component parts and determining their individual contributions which depend on their sizes, shapes, and thermal properties. Examples of the break down are given, and graphs and simple formulae provide data from which the thermal properties of such simple components as discs, shafts, bushes and so on can be found. The method formalises the procedure for combining the thermal resistances to obtain that for the assembly by using a network procedure and rules for combining heat paths through components in series or in parallel; the procedure is explained, the rules specified, and the final result gives the lower and upper limits for the thermal resistance of the assembly. ESDU 78029 gives data for estimating the heat dissipation from the assembly, and ESDU 79002 gives comprehensive worked examples illustrating the use of the methods. ESDU 78027 provides a first estimate of temperature rise and should be consulted first to decide whether the refined analysis of ESDU 78028 and 78029 is necessary for any particular case.