Final answer:
The correct approach when a motorized vent damper is not available in the Equipment Type menu is to not modify the default Flue Diameter value. The average speed of air in the main uptake air duct can be calculated using the volume of the house and the cross-sectional area of the duct.
Step-by-step explanation:
If a motorized vent damper is not an option listed in the Equipment Type drop-down menu, you should not modify the default Flue Diameter value. In other words, the correct answer to this question is D) Do not modify the default value. However, to solve for the average speed of air in the duct based on the provided question, we first need to calculate the volume of the house's interior, which can be done by multiplying the width, length, and height of the house's interior dimensions. Next, we determine the volume of air that passes through the duct in 15 minutes and calculate the cross-sectional area of the duct using its diameter. With these values, we can then calculate the average speed of air in the duct.