What is a common method for measuring air flow rate in ducts?

The correct method for measuring air flow rate in ducts is the use of an anemometer. An anemometer is specifically designed to measure the velocity of air, which can then be used to calculate the flow rate through a duct. This device works by capturing air movement and providing a reading related to the speed of the airflow, allowing technicians to assess air distribution and ensure systems are functioning properly.

In contrast, a thermometer measures temperature and is ineffective for determining airflow metrics. A barometer is designed to measure atmospheric pressure and likewise does not provide relevant information about airflow rate. A hygrometer, which measures humidity levels in the air, is not applicable for direct airflow rate measurements. Each of the other options serves a distinct purpose unrelated to airflow measurement, reinforcing the importance of selecting the appropriate instrument for specific HVAC diagnostics.