What is the primary purpose of insulating the outside of a duct?

The primary purpose of insulating the outside of a duct is to prevent heat loss. When ductwork carries heated air, insulation helps to maintain the temperature of that air as it travels through the ducts. Without insulation, heat can easily escape into the surrounding environment, leading to increased energy consumption and reduced efficiency of the heating system. This is particularly important in areas where ducts run through unconditioned spaces, such as attics or crawl spaces, where significant temperature differences can occur.

Proper insulation also helps to maintain the desired comfort level in a building by ensuring that the air delivered to rooms is at the correct temperature. Overall, insulating ducts is an essential practice in HVAC systems to enhance efficiency and performance.