Many of us have been in situations where we struggled to solve a customer's comfort problem. No matter how efficient the HVAC equipment, or how good the duct system, you couldn't find the answer. It's a frustrating and helpless position to find yourself in.
Some comfort and indoor air quality issues we encounter bleed over from areas that we might be unfamiliar with. The most common are the influences of building construction, like leakage and insulation. Knowledge of these subjects, like how a building interacts with an HVAC system, and how the building is part of the duct system are invaluable when you encounter a comfort problem missing an obvious answer.