What is a common source of leaks in ductwork?

Poorly sealed joints are a common source of leaks in ductwork because they are the points where two segments of duct connect. If these joints are not adequately sealed using appropriate methods, such as mastic, foil tape, or mechanical fasteners, air can escape from the duct system. Air leaks reduce the overall efficiency of the HVAC system, leading to higher energy costs and reduced comfort in conditioned spaces. Additionally, leaks can impact system pressure and airflow, potentially causing strain on HVAC components and leading to premature wear or failure.

Regarding the other options, while improper insulation can lead to energy loss and condensation issues, it doesn't directly cause air leakage in the way that unsealed joints do. Excessive duct length can lead to increased resistance and airflow challenges but doesn't inherently create leaks either. Similarly, sized ducts that are correctly tailored to the system's specifications will operate efficiently and are not a typical source of leaks if installed properly.