The probabilistic model (PROMO) applied to the problem of air infiltration in low-rise buildings is presented. The PROMO model allows the estimation of the effect of variations of climaticconditions on air exchange in a building. In PROMO, experimental data are used in order to evaluate the parameters and types of the distributions of temperature, wind speed, and wind direction. Those distributions are employed to evaluate the distributions of air change rate caused by air infiltration and can be used to estimate probability of inadequate ventilation. FORM (First-Order Reliability Method) technique is used for probabilistic approximations. For validation of the PROMO model, the probability density functions of the air change rate for the test house situated near Gothenburg are estimated from the results of full-scale measurements of pressure differences across the envelope and compared to those calculated by PROMO from the climatic parametersmeasured at the site. The agreement of the results obtained in these two ways is very good.