What would be a direct consequence of improperly sized ducts in a ventilation system?

Improperly sized ducts in a ventilation system can lead to higher indoor humidity levels, making this the correct answer. When ducts are not correctly sized, airflow can become restricted or uneven, which can prevent adequate moisture removal from the indoor environment. This disrupted airflow can lead to areas of low ventilation where humidity can accumulate, creating conditions that might promote mold growth or other issues related to excess moisture.

In contrast, options that suggest increased airflow efficiency, enhanced thermal comfort, or noise reduction are unlikely to occur with improperly sized ducts. Instead of improving performance, poorly sized ducts often create inefficiencies, leading to uncomfortable indoor environments and potentially higher energy costs due to the HVAC system's added strain. The aim of ventilation systems is to maintain optimal humidity levels as part of creating a healthy indoor environment, and this system’s effectiveness hinges significantly on the sizing of the ducts.