According to the Duke study, wherever water was available, microbial growth could be found on any surface of the HVAC system, including metal "flex" duct, the flat surfaces of metal ducts, plastic-lined flex duct, caulks and sealants, conditioning coils, metal sound attenuators, mixing box dampers and internal duct liners.

The Duke researchers strongly suggest that removing excess water from supply air will minimize conditions that can result in sustained microbial growth.