The utilisation of empirical correlations for the estimation of thermodynamic functions is a valuable approach for reducing experimental effort and for validating existing data. Established correlations and group contribution methods provide reliable heat capacity estimates for simple organic compounds. The present work assesses the extent of deviations introduced by employing conventional heat capacity correlations for diols. For this purpose, heat capacity differences between the solid, liquid and gas phases are evaluated based on experimentally determined vapour pressures, enthalpies of vaporisation, heat capacities in the solid and liquid phases, and quantum chemical calculations. It is demonstrated that the structural characteristics of diols result in a significant overestimation of heat capacities when conventional empirical methods are applied. Deviations in the range of 30–50 J·K−1·mol−1 were observed when compared to consistent experimental data. As part of the evaluation, new group contribution parameters were developed for calculating heat capacities in the solid and liquid phases. Based on these improved data, inconsistencies in literature values for enthalpies of vaporisation (on the order of 10–15 kJ mol−1) could be resolved. Furthermore, a new correlation was derived that allows for the reliable prediction of enthalpies of vaporisation for α,ω-alkanediols from pentanediol to decanediol. The resulting data provide significant advantages for the design of technical processes involving diols as renewable sources and for the accurate modelling of their phase behaviour.