Humidity sensors are affected by the air quality in livestock buildings. New sensor models should be tested under actual barn conditions to assess their long-term integrity. An experimental procedure was developed to meet this requirement. After initial static and dynamic calibrations in a specially designed humidity chamber in the laboratory, the test sensors were installed in a livestock building for one year. Several times during the year, the sensors were temporarily removed from the barn and taken back to the laboratory for calibration against a reference hygrometer ad determination of static and dynamic properties including accuracy, hysteresis, and time response. A bank of 72 TDK humidity sensors with different filters and coatings were evaluated with this procedure in a grower/finisher room. The drift of various static and dynamic sensor characteristics over time, the reliability, and the durability of the sensors were identified and the best sensor treatment was selected. The results confirmed the value and practicality of the test procedure, and led to recommendations for the appropriate length of the in-barn evaluation period, calibration frequency, and required replication.