Infiltration or in other words the air leakage in buildings has an important role on heat load calculations. The rate of this loss has been estimated as 20 to 30 % of the total load. The indicated important effect of infiltration on the load calculations needs a reliable method for the determination of air leakeage level in buildings. Meantime, the rate of infiltration has an additional importance at the area of thermal comfort studies which deals with the air quality of enclosed volumes. During this research study, first the mechanism of infiltration and the major components of the phenomena (wind pressure, temperature difference) was discussed together with the theoretical considerations. Later, several conventional engineering approachs and emprical methods was reviewed and compared among each others. At the last part of the paper, the modified DIN 4701 method which is presently used in Turkey, and some other algorithms was applied to some pilot buildings and the predictions was compared with experimental results