We were commissioned by a global property management firm to investigate the causes of water damage to, and water staining of, the duct liner on certain office floors of a high-rise office building in New York City, and to recommend corrective action. The water staining of the duct liner was found to be seasonal in nature; therefore, the investigation focused on changes in moisture and temperature of the ventilation and supply air streams as processed by the HVAC equipment. A data collection plan was developed with the use of strategically located portable data loggers together with data from the building’s automation system to track the temperature, relative humidity, and humidity ratio of ventilation air throughout the cooling season. Based on an analysis of the cooling season data, we determined that moisture damage to the supply air ductwork was caused by the current operation of the chilled water coil in air handling units on each floor of the building, which never allowed the duct liner to dry out. The recommended solution involved reprogramming the building’s automation system to achieve operational settings that maintained occupant comfort while keeping the interior of supply ducts dry.