Much like a crawl space, ductwork in an attic is subject to the environment in the attic. The duct lines heat up to the same sweltering temperatures in the attic during summer months, which often reach over 100-degrees. We pump cold, 55-degree air through the duct lines that are heated up. Imagine trying to cool a room to 75-degrees with 75-degree air. It's going to take a long time!