Accuracy requirements are based on the flow hood application. A poorly calibrated flow hood and sensitivity to grill flow variances, result in an over or underestimation of flow by 25-35%. Also, one must consider original design specifications of the HVAC system and if any room changes have been made. A great original duct design and a new HVAC system originally did everything it was intended to do, however, poor HVAC maintenance, room modifications without design re-work, and changes in source conditions, will result in building related issues. Flow hoods are useful and are sometimes limited to the application such as duct breakage, room comfort, and duct leakage. The change in airflow pattern between calibration and application creates large flow measurement errors.