A flow hood is a portable testing device that measures air velocity or volumetric flow rate directly at registers, grilles, and diffusers without requiring duct access. The technician places the hood over the outlet, and an internal sensor calculates airflow in cubic feet per minute (CFM). This non-invasive method provides quick verification of supply and return airflow at individual points.
Operation and Accuracy
Flow hoods measure airflow ranging from 100 to 2,000 CFM depending on model specifications. The device displays results within 5 to 10 percent accuracy for properly sized registers. Modern digital flow hoods feature LCD screens and data logging capabilities. Accurate measurements require placing the hood perpendicular to the outlet and allowing airflow to stabilize for 5-10 seconds before recording.
Field Applications
Flow hoods serve as primary tools for balancing supply registers, verifying design airflow specifications, and identifying blocked or undersized outlets. They complement pitot tube traverses and ductwork inspections during system commissioning. This method is particularly useful for residential and light commercial applications where multiple register measurements quickly reveal system imbalances without invasive duct opening.