In buildings for animal husbandry, it is unconditionally necessary to create the required microclimate by building-technical and operational measures. Ventilation of buildings for animal breeding is one of the means how to provide it. Ventilation system is a part of technical equipment in buildings and stalls for breeding of animals. Ventilation systems are designed for particular breeding conditions, for individual species and categories of animals, climate zone in connection to building and technological method of solution. They must take into account all specificities, which arise from differentiated breeding conditions. Their main role is exhaustion of superfluous heat, air humidity and harmful gases produced in the building. Their dimension is proposed from requirements on effectiveness of ventilation, amount of ventilation air. Another important role is compensation at increased air temperatures by its greater movement according to valid principles of calculation of criteria for individual animal categories and of the recent knowledge in the given sphere at the same time. There is also requirement to reduce high temperatures of air by its cooling. Present building and technological methods enable the decrease by approx. 5 K.