Sitting in an office, or in their own homes, many people don’t notice their building’s ductwork unless there is something wrong with it — it’s too noisy or the air in the room is too cold or too hot.

Homeowners know when a duct problem arises. They know when a room is too warm or too cold. But they might misdiagnose the cause. “They are under the assumption that when they get a new a/c system, ...