I am a homeowner (not a contractor) and installed the ductwork on my remodel job. The ductwork was so tight above the bathroom (finished room above it) that, rather than using the fiberglass batt duct insulation that I used everywhere else, I asked the spray foam contractor to shoot the ductwork in the space above the bathroom with spray foam. The round metal ducts are screwed and sealed with mastic. Now of course the city hvac inspector is telling me this is a code violation and is telling me to scrape all the spray foam off the ductwork and wrap it with fiberglass. I understand that "the code is the code," but is there some drawback to using spray foam insulation on ductwork besides the difficulty I am going to have removing it? Is it approved anywhere??? thanks
I would think it is not rated for a high enough temperature. I have seen furnaces malfunction because of a faulty or miswired limit control and get hot enough to melt the A/C coil drain pan. Fibreglass is not as sensitive to high temp. Foam may gas off and release harmful vapors also.