The purpose of the research was to compare uncontrolled air exchange at nurseries with different air inlet solution. Four identical 400 m² nursery departments were investigated. Three of them used porous ceiling as an air inlet, with different area of ceiling designed to be permeable. The areas of porous ceiling tested were 300, 150 and 75 m² respectively. In fourth department ventilation air entered the room through, also located in the ceiling, high speed inlet systems. Actual air exchange in the departments was evaluated from H₂O balance. The data required for calculation, i.e. inside and outside temperatures and humidities were being continuously monitored and registered from mid of December, 2000 to early February, 2001 to include first 5 weeks after moving piglets to each departments. Propane consumption was checked every day. U – value for the outside walls was calculated and additionally checked by means of thermovision. The number of piglets moved t