The University Center for the Study of Energy Problems (CUEPE) is a multidisciplinary group interested in the eficient use of energy. We consider both technical and economical aspects of energy systems and the work involves engineers, architects, and physicists. We are anallying some buildings by different methods and have found that simplified methods, based on limited but relevant measurements and parameters, may be compared satisfactorily with other classical and more complex methods and give useful and valuable information. We will discuss some of them.