The present study shows a new way to calculate a geothermal installation. The process consists in measuring the temperatures inside a perforation. Once we have this parameter, we'll be able to determine the total depth of the perforations in a geothermal installation. With this method, it'll be possible to dispense with other studies which are being used at the moment in this kind of installations. This fact will mean important economic savings and easier works. Based on the "Principles of Thermodynamics and Fourier Law", and using the temperature values and other initial data, it was possible to determine the total perforation depth. During this process the software "Earth Energy Designer" was also used. (C) 2015 Elsevier Ltd. All rights reserved.