In order to control the environment within a poultry house it is essential that a producer not only controls how much air is entering the house, but where it is entering. For instance, during cold weather essentially no air should enter a house when the fans are off. When the fans are operating, all the air should enter through the air inlets so it can be directed along the ceiling toward the center of the house to insure it is tempered by the warm air next to the ceiling before moving down to b...ird level. Air entering through cracks or gaps in side wall curtains either when the fans are on or off can lead to drafts, caked litter, and excessive fuel usage. During the summer, in order to maximize bird cooling all incoming air should enter through a house’s evaporative cooling pads. Air entering through cracks leads to hotter side walls, increased temperature differentials between the pads and fans, as well as poor air speed distribution; all of which can reduce weight gains and increase feed conversions. To minimize the problems associated with air leakage it is essential that poultry producers are aware of how tight their houses are so that corrective actions can be taken before bird performance suffers and/or heating costs become excessive.