The paper gives results of an investigation of the potential antimicrobial efficacy of sealants used in heating, ventilation, and air-conditioning systems. Recent experiments confirm field experience that duct cleaning alone may not provide adequate protection from regrowth of fungal contamination in fiberglass duct liner. Current recommendations for remediation of fungally contaminated fiberglass duct materials specify complete removal of the materials. But removal of contaminated materials can be extremely expensive. Therefore, a common practice in the duct cleaning industry is the post-cleaning use of antimicrobial surface coatings with the implication that they may contain or limit regrowth. The paper describes a study to evaluate whether three commercially available coatings, placed on a cleaned surface that 1 year previously had been actively growing microorganisms, would be able to prevent regrowth. The three coatings contained different active antimicrobial compounds.