Ductspec: HVAC Duct Sizer

Duct calculator for HVAC installers, techs and sheet metal shops. 800 CFM at 0.08 friction rate: 14 in round at 750 fpm, or 16 × 10 in rectangular. Pay once. No subscription, no account, no ads. Works offline. No data collected. WHAT YOU CAN DO • Size a duct: enter the airflow and a friction rate or a velocity. You get the exact and the standard round diameter, the rectangular equivalent for the side you choose, and the velocity and friction at that size. • Convert round to rectangular and back, with equivalent sizes for several heights and an aspect-ratio check. • Check velocity and pressure drop for a trunk, branch or runout over a run length, against typical residential and commercial velocity guidelines. Straight duct only: fittings, coil and filter are not included. • Work out room CFM from air changes per hour, or the air changes a fan gives. • Apply the fan laws: new CFM, static…