CODYBA is a software addressed to designers, teachers and research organisms. This software determines the energetic fluxes of a building zone. The basic data are the zones geometry and constitution. The main parameters are the climatic conditions, the internal loads and the heating and air conditioning powers, as well as their regulation mode. The graphical interface introduces concepts that are identical to those manipulated in the everyday practice by the building professionals and that are reproduced on screen by a classic "iconographical" representation in the "Windows" environment.