Which instrument is commonly used to measure return airflow to a gas furnace?

The anemometer is the appropriate instrument for measuring return airflow to a gas furnace. This device works by measuring the speed of air movement, typically in cubic feet per minute (CFM). In the context of HVAC systems, anemometers provide valuable data on the airflow, which is crucial for assessing system performance, efficiency, and ensuring that the furnace operates within its designed specifications.

Understanding the return airflow is vital for proper combustion and ventilation, as well-balanced airflow ensures the gas furnace operates efficiently and safely. If the airflow is too low or too high, it can affect the furnace's heating capability and potentially lead to safety hazards.

Other instruments are used for different measurements. A barometer measures atmospheric pressure, which is not related to airflow measurement. A thermometer measures temperature, which provides information about the thermal environment but not airflow speed or volume. Likewise, a manometer is designed to measure gas pressure in systems, such as the pressure within gas lines or combustion chambers, rather than airflow itself. Therefore, the anemometer stands out as the most suitable tool for this specific application in HVAC practices.