What is the standard for the installed duct insulation thickness used for determining thermal resistance?

The standard for determining thermal resistance in installed duct insulation is based on the concept of full thermal effectiveness. The correct choice regarding insulation thickness is the full thickness of the insulation as installed, which relates directly to its efficient performance in thermal resistance. In practical terms, when assessing duct insulation, it is crucial to consider the actual effective thickness that contributes to thermal resistance, rather than a reduced value.

Nominal thickness may suggest the design specifications or standard measurements, but it may not accurately represent how much insulation is actually functioning in real-world applications, especially if compression or damage occurs. By using the full thickness of insulation, professionals can ensure that they are considering the insulation's true capacity to resist heat transfer.

While some options suggest using a percentage of the nominal thickness, these figures typically result in an underestimation of the insulation's performance. Therefore, the best practice in evaluating insulation effectiveness is to rely on the full thickness to ensure that thermal resistance is measured accurately and effectively, aligning with industry standards and codes.