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Tap any result in Ductline and it opens: the equation, your own figures substituted into it, and the standard it follows. A duct calculator that disagrees with the one in your other hand is worthless until you can see which of them is wrong.
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What it does
- Sizes round, rectangular and flat-oval duct by friction rate or velocity, in any direction — size from airflow, airflow from size, pressure drop from either.
- Solves the real physics. Colebrook–White for the actual friction factor from 12 published material roughnesses; air density and viscosity corrected for temperature and elevation; flex compression at 4, 15 and 30%.
- Static pressure you can defend. Total external static against the blower's rated ESP, a component worksheet, ACCA Manual D total effective length, 25 fittings with ASHRAE loss coefficients, leakage by sealing class.
- Fabrication, both standards. SMACNA gauge and pressure class, or EN 1505/1506/1507 sheet in millimetres; every suggested size snaps to one that actually exists.
- The whole job. Projects, runs and segments with client and notes, and a one-page PDF per run or per project that prints the method and every warning.
What it doesn't do
No sign-in. No subscription. No advertising. No analytics. No network needed — the places you need it are crawl spaces, plant rooms and attics. Nothing you type leaves your phone. Here is the whole privacy policy; it is short because there is nothing to disclose.
Ductline is a design and verification tool for a competent HVAC professional. It does not perform load calculation and does not certify a design for permit. Fabrication tables follow SMACNA and EN; verify against the standard your jurisdiction enforces.