Does both supply and return duct need to be insulated?

Yes, both supply and return ducts should be insulated, especially if they run through unconditioned spaces like attics or crawl spaces. Insulating the supply duct helps maintain the temperature of the conditioned air as it travels to rooms, while insulating the return duct prevents heat gain or loss, ensuring efficient airflow. Proper insulation can enhance energy efficiency, reduce energy costs, and improve overall comfort in a building.