What is the minimum level of insulation that a portion of a supplied duct that is on an exterior of a residential structure requires if the duct is greater than 3 inches in diameter?

The minimum level of insulation required for a portion of a supplied duct that is on the exterior of a residential structure and has a diameter greater than 3 inches is R-10. This level of insulation helps to ensure proper energy efficiency and performance by reducing heat loss or gain through the ductwork, which can be particularly important when ducts are exposed to outside temperatures.

Ducts with inadequate insulation can lead to significant energy waste, as conditioned air may be heated or cooled before it reaches its intended destination. By specifying R-10, building codes and standards seek to maintain a comfortable indoor environment while also promoting energy conservation practices.

The other levels of insulation, such as R-15, R-20, and R-5, either exceed what is necessary for this application or do not provide sufficient insulation. R-10 strikes the right balance for effective insulation in the context of exterior ducts under standard requirements.