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.