When planning geothermal projects, a mathematical comparison is made using an algorithm that maps the various probe designs using software that carries out the thermodynamic calculations for these probe types using the same basis and method. The ModTherm program developed by the authors is used for this purpose. After this selection, a technical, geothermal and economic comparison can lead to the best possible estimate that can be used as a basis for project development and planning. The presentation will compare common probe types on the market.