The heat and mass transfer analogy is used in building simulation to convert heat transfer coefficients into mass transfer coefficients. The analogy is valid under strict conditions. In this paper CFD is used to investigate the accuracy of the analogy for indoor air flows when not all these conditions are met. CFD simulations confirm the possibility of applying the analogy to indoor air flows and show that when not all conditions are met, the average mass transfer coefficients remain well predicted by the analogy while the prediction of local transfer coefficients can result in large errors. (C) 2008 Elsevier Ltd. All rights reserved.