Maintaining acceptable thermal and gas concentration levels during minimum ventilation periods is challenging. The small amount of fresh-air used during cold weather periods needs to be distributed as uniformly as possible through the planned inlet system. Unfortunately, leaks and cracks throughout a barn provide unplanned air inlets at sporadic and unpredictable locations, rendering the ability to uniformly distribute minimum ventilation air nearly impossible. This project focused on quantifying leakage rates from swine finishing barns to characterize the significance of barn leakage, and, to provide guidelines for reducing this leakage. Our results, based on 17 swine finishing barns, indicated that the as-is infiltration rate, at an operating static pressure of 0.08 in wc, averaged 5.96±1.49 CFM/pig; with the leakage rates through curtains, fans and other components consisting of 1.49±1.00 CFM/pig (about 25% of as-is), 1.52 ±1.38 CFM/pig (about 26% of as-is) and 2.90 ±1.42 CFM/pig (about 49% of as-is), respectively. These rates apply to finishing barns with 8 ft ceilings and a stocking density of 7.5 ft2/pig. The as-is leakage rate was minimum for rooms from single room barns (5.85 ±1.66 CFM/pig at 0.08 in wc) and rooms having non-metal ceilings aged ≤ 13 years (5.85 ±2.15 CFM/pig at 0.08 in wc). Curtains, pump-outs, and unused cold weather fans are manageable leakage points that can be mitigated with relatively low-cost methods that many producers are presently incorporating. The remaining 50% of the as-is leakage, primarily identified from ceiling-to-side/end wall joints and ceiling panel corrosion locations will require significant effort to mitigate, potentially with attic spray foam insulation. If spray foam is used at these targeted locations, a reduction of 80% in overall leakage rate was measured in a controlled test room. If infiltration is not controlled and the barn is operating at the as-is leakage rate, a maximum most likely operating pressure (in wc) for delivering 2, 4, and 6 CFM/pig is 0.001, 0.011, and 0.042 in wc, respectively with unplanned leakage openings accounting for 91%, 86%, and 82% of the inlet area required. If infiltration is controlled up through attic foaming, the maximum most likely operating pressure for delivering 2, 4, and 6 CFM/pig increases 0.039, 0.072, and 0.073 in wc, respectively with unplanned leakage openings accounting for 48%, 29%, and 19% of the inlet area required. For more information, please contact Dr. Steve Hoff, Department of Agricultural and Biosystems Engineering, Iowa State University (