A duct flow meter is a device used to measure the rate of air flow in a duct system. It is typically used in HVAC systems to measure the air flow rate of air being supplied to a room or building. Duct flow meters measure the velocity of air in the duct, which is then used to calculate the volumetric flow rate. The most common type of duct flow meter is the hot-wire anemometer, which uses a heated wire to measure the velocity of the air. Other types of duct flow meters include pitot tubes, orifice plates, and vortex shedding flow meters. Duct flow meters are an important tool for maintaining proper air flow in HVAC systems, as they can help identify blockages or other problems that may be affecting the air flow.