Greenheck’s Toolbox includes a Fan Law Calculator and a Ductulator App. To use the Fan Law Calculator, input existing rpm, cfm, static pressure, and horse power. Modify any one measurement and the remaining three calculate. Greenheck’s Ductulator app allows you to quickly and easily size HVAC duct. Input your duct shape, rounded dimension, air temperature, elevation and select roughness. Next determine sizing by airflow or dimensions, select velocity or friction factor, input your volume, velocity, aspect ratio and calculate. Your results will be displayed.