Computational Electromagnetics (CEM) is a domain which provides numerical solutions to compute an- tenna performance, electromagnetic compatibility, radar cross section and electromagnetic wave propaga- tion. The ever-increasing need for more precision and larger meshes raises the natural question whether it is worth porting CEM algorithms to computer grids. Due to the nature of the computations, CEM al- gorithms are not trivially parallelisable, as data dependency inside the mesh implies communication. The goal of this paper is to answer the question: given a set of resources, what is the subset of resources one should chose among, to minimise the time it takes to solve a CEM problem. After presenting a model of the application execution time, several algorithms for selecting resources are described. The limits of the theoretical model is then compared against experimental results, obtained from the Grid'5000 platform.