This article presents the first application of the Sim_Zonal software, a tool for evaluating indoor temperature and air flow distributions for residential and office buildings. The aim of this EDF (Electricity of France) software developed with the LEPTAB (University of La Rochelle) is to evaluate comfort problems and specially risks of discomfort (risk of draught, indoor gradient temperature, etc..) for rapid technical appraisals. The tool development - under Windows 95 - is in progress. In this paper we present our first application : an evaluation of the air temperature distribution in an cell heated with a heated floor.