It has been proved in the past, with common liquids, that the values of their thermophysical properties have a significant effect on the design of physicochemical processing and reaction units, influencing directly the design parameters and performance of equipment like heat exchangers, distillation columns, and reactors. In this paper we have analyzed the effect of the uncertainty of thermophysical data of ionic liquids (density, heat capacity, thermal conductivity, and viscosity) in the design of some current equipment, used ill processes as solvents or heat transfer fluids. Data have been collected from the IL Thermo database for alkylmethylimidazolium (C(n)mim) liquids, with [BF(4)] and [PF(6)] anions. Results obtained show that the influence of actual errors in the thermophysical properties of ionic liquids can render any future design as not working or excessively costing. Moreover, the heat storage capacity of these ionic liquids has been analyzed. and it is possible to consider them as possible replacements Of Current silicon-based heat transfer fluids, The results obtained Support that the implementation of those applications needs a careful selection of experimental data, otherwise equipment will be either under- or overdimensioned, with the consequent ill operation or increased capital costs. In addition, they recommend a revision of the present methods of measurement of thermophysical properties of ionic liquids and the establishment of reference data on thermophysical properties with low uncertainty, to avoid the actual status of experimental data.