Should I insulate metal duct work in basement?
They make insulation that is like a foil and fiberglass blanket that you wrap square ducts with, if you are in a high humidity area you may find the duct will sweat if not insulated because your ductwork close to the air handler will be 20-30 degrees lower than the room temp causing the condensation. I might wait and see. Just google duct insulation and you will see the different types.