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Four models of aspirated psychrometers were constructed and tested for accuracy, reliability and maintenance requirements over a 13-week period in a swine barn and over a 26-week period in a poultry barn. Model WF was a conventional aspirated psychrometer in which a wick was used to transfer water from a water reservoir to the wet-bulb temperature sensor. Model NF was identical except that the air filter on the psychrometer was removed. In model SP, water was sprayed onto the wet-bulb sensor. In model MO, the wet-bulb covering was mechanically dipped into a water reservoir. A commercial non-aspirated psychrometer also was tested. Models SP and MO required less maintenance than models WF and NF and gave consistently accurate relative humidity data. Model WF performed better than model NF in the swine barn, but the opposite was true in the poultry barn. The maintenance requirements for models WF and NF were less, and the accuracy was better, when the psychrometer fans were operated only intermittently. The commercial non-aspirated psychrometer consistently gave relative humidity measurements 10% higher than a reference psychrometer.