We pulled every supply plenum and the ductwork today, and even I was surprised by what we found. Quick refresher: the supply plenum is the box that sits after the air handler and your filter that feeds air into the ducts. I showed three different plenums, and all three had mold inside. The worst one lived between the 1st and 2nd floor. The growth was literally 3-D, sticking out from the plenum walls. This is the air you breathe. How does this happen? • Air leaks pulling in humid outside air into