To ensure accurate airflow readings, the fan system's airflow should be checked using which of the following?

Checking the fan system's airflow for accurate readings can be achieved using various tools, each serving a distinct purpose. Utilizing a manometer helps measure pressure differences, which can indicate airflow changes, particularly in duct systems. A flow hood is designed to capture air flowing from a grille or register, providing direct airflow measurements often in cubic feet per minute (CFM). An anemometer, on the other hand, measures the speed of air movement at various points, allowing HVAC technicians to assess airflow efficiency and performance.

Since all three tools—manometers, flow hoods, and anemometers—provide valuable information regarding airflow, it is appropriate to use any of them based on the specific measurement or condition being evaluated. Consequently, choosing to check the airflow using all these instruments ensures comprehensive and accurate airflow readings, making option D the best choice.