As you’ve discovered, warm attics aren’t good. They lead to icing, leaks and wasted energy. That’s why keeping the attic cool in winter is necessary, but the main approach should involve duct insulation. There are several options that make sense, depending on your specific situation. If the ducts run close to the attic floor, box them in with an insulated framework. If this isn’t practical, consider having them replaced with factory-insulated metal duct.