Final answer:
To reduce an excessively high draft through a furnace, the barometric damper should be adjusted to a more closed position, reducing the flow of air and restoring proper combustion conditions.
Step-by-step explanation:
When the draft through a furnace is too high, it indicates that the flow of air through the furnace is excessive, which can lead to poor combustion and potentially unsafe operating conditions. To correct this issue, one needs to adjust the device that regulates the airflow. The appropriate action, in this case, would be to adjust the barometric damper to more of a closed position, which is option (c). By doing so, the damper restricts the amount of air being pulled through the system, thereby reducing the draft to a more suitable level.
The barometric damper is designed to maintain consistent draft by automatically adjusting to variations in atmospheric pressure and wind conditions. In contrast, increasing the primary air adjustment would actually increase the draft, while adjusting the burner motor would mainly affect the fuel input rather than the airflow.