To change the cubic feet per minute (CFM) delivered by a single-speed belt-driven blower, what should the technician adjust?

To alter the cubic feet per minute (CFM) delivered by a single-speed belt-driven blower, the technician should adjust the motor pulley size. This is because the relationship between the pulley sizes and the blower motor affects the rotational speed of the blower. When the motor pulley size is changed, it can increase or decrease the speed at which the blower operates. A smaller motor pulley will increase the blower speed, thus delivering more airflow (higher CFM), while a larger pulley will reduce the speed and lower the CFM.

Adjusting the blower size or duct size does not directly change the speed of the blower and can result in inefficiencies or issues with airflow. Similarly, changing the furnace setting may alter the operation but it does not directly impact the CFM provided by the blower in a straightforward manner. Focusing on the motor pulley allows for precise control over the blower's output.