HEPA filter manufacturers must ensure that their filters are tested accurately and must do so in a cost efficient way. This study describes tests that tried to determine the minimum time required to provide statistically significant efficiencies of HEPA filters using a test system that is currently used in the production of the filters. 300 filters were tested. Poisson distribution was used to describe the variations and to find the upper and lower levels with 95% confidence. The results found that it takes 90 seconds for the test to ensure that a filter has an efficiency of 99.99% or higher at 95% confidence. For a new test system, software is suggested to calculate the confidence limits of the filters efficiency after each test cycle and then determine determine weather to continue testing.