What is the best procedure to increase the speed of a furnace blower?

To increase the speed of a furnace blower, adjusting the motor pulley by closing it up is an effective procedure. When you close up the motor pulley, you effectively increase the speed at which the blower operates. This is due to the relationship between the size of the pulley and the rotational speed of the motor; by making the pulley smaller in diameter, the motor must turn faster to maintain the same output speed at the blower.

In the context of the other options: changing the motor type typically involves replacing the entire motor, which is not only costly but may also not guarantee an increase in speed without the right specifications. Increasing the voltage supply to the motor can lead to potential damage or burning out the motor, as it may exceed the motor's capacity; hence, it is not a safe or standard procedure for adjusting blower speed. Adjusting thermostat settings primarily affects temperature regulation and does not directly influence the speed of the blower itself.

By closing the motor pulley, the adjustment leads to improved airflow while maintaining efficiency and reliability in the operation of the furnace blower.