One of the methods to protect a building with a high indoor moisture content and structural glazing from vapour condensation is to use energy-efficient windows [1,2], but often, it is not sufficient. Another method is to blow air with a relatively low water content over a glazing. Such systems are designed to cope with critical conditions, i.e., the lowest temperature of the external air and the highest water content in the indoor air; therefore, they are extremely energy-consuming. The authors propose to use demand-controlled ventilation systems [3-6] that can adjust air consumption according to the actual temperature and indoor air humidity. The efficiency of air jet protection depends on the air stream range, conditions of heat exchange on the surface, and changes in the moisture content in the boundary layer of the air stream. The article [7] describes the method for the determination of the dew point temperature on the glazing surface that accounts for the characteristics of the air stream flowing out of the slotted outlet. This article analyses a refined statement of the problem that accounts for the change in the heat-exchange conditions in the initial and main parts of the air stream. (C) 2014 Elsevier B.V. All rights reserved.