Duct Cleaning 101

It’s common to find internally lined supply ductwork used throughout buildings constructed in prior decades. Within the past few years, we’ve worked with a number of Owners that have experienced a common symptom with these internally lined supply duct systems: mold growth, evidenced at times by visible release into the airstream and the rooms served. There are a number of factors that contribute to this symptom including (but not limited to) a moisture laden airstream, mold spores, and mold “food” (dust/organics on the internal insulation). Owners have sometimes tried cleaning (only) inside the ductwork, with the symptom subsiding for awhile but eventually returning. What can be done? Certainly replacing the old internally lined ductwork with new externally insulated ductwork is an option. However, the duct replacement process can be very costly and disruptive to building operations. In most cases, replacing the ductwork is not feasible due to cost and/or disruption. Owners end up having the ductwork cleaned...and then cleaned again…and again. TGCE has successfully implemented an alternative solution. While the process described below is not necessarily new, it has been improved over the years. And as with any other job, the experience and care brought to it by the individuals performing it greatly affect the results. The solution includes gently but effectively cleaning the inside surface of the duct liner, “fogging” inside the ductwork with disinfectant, and then applying an anti-microbial coating to the surface of the duct liner. The coating serves two purposes: it encapsulates any leftover contaminants residing within the insulation (i.e. not on the surface), and it prohibits mold growth in the insulation and on its surface. The pictures below represent before vacuum cleaning, after vacuum cleaning, and after coating conditions of internally lined ductwork. It’s all a little different than what the movies portray, huh? When considering this solution, it’s important to note that holes must be cut at strategic locations in the ductwork. In addition to allowing the cleaning, fogging, and coating processes to occur, these holes are used to visually inspect the inside of the ductwork after each step. As a rule of thumb, holes are needed upstream and downstream of fittings (elbows, offsets, etc.) and can serve up to 25 ft. of straight ductwork. ~ Greg Canter, P.E., LEED AP - Senior Engineer