The balometer is a specific flow meter for measuring the flow rate of the air leaving or entering a ventilation outlet within the airflow system of a building. Some balometers can also measure the temperature and relative humidity of the air stream along with its flow rate, as well as the atmospheric pressure of the room. 

Modern balometers measure the velocity and flow rate of an air stream using a differential pressure measurement system, which is very reliable and accurate for this type of application. This technique uses a measuring grid with many holes through which the pressure is measured in comparison to the atmospheric pressure, and provides an average flow rate over the entire measuring area.