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HVAC Duct Flow
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About the app

HVAC Duct Flow sizes rectangular and round air ducts and checks grilles and diffusers — fast, offline, with live results while you turn the airflow dial.

Features

Rectangular ductConstant velocity, equal friction, check by size; a×b options from 1:1 to 1:4 with the recommended size
Round ductSpiral duct sizing to EN 1506 standard diameters
Equivalent conversionRectangular a×b → round Ø (Huebscher De) and round Ø → rectangular options
Grilles & diffusers8 types: velocity, pressure drop and throw, with an occupied-zone view
CorrectionsDuct material roughness, air temperature and altitude
PDF reportOne-page report, shared from your device
UnitsMetric and imperial (m³/h, l/s, CFM, Pa, in.wg …)
15 languagesTR, EN, DE, FR, ES, IT, PT-BR, RU, PL, AR, ZH, JA, KO, ID, VI

Frequently asked questions

Which methods and standards are used?

Duct friction uses Darcy–Weisbach with the Colebrook equation (ASHRAE Fundamentals, Duct Design). Rectangular ducts use the Huebscher equivalent diameter; friction is that of the equivalent round duct at the same airflow. Sizes follow EN 1505 (rectangular, 50 mm steps) and EN 1506 (spiral diameters) and are always rounded up.

How is the recommended rectangular size chosen?

Among the sizes that meet your target velocity or friction, the one with the smallest perimeter (least sheet metal) is recommended; on a tie the lower height wins, which fits ceiling voids better.

Why can grille results differ from a manufacturer's catalogue?

Grille results use typical literature coefficients (free area ratio Ak, loss coefficient ζ, throw constant K). Manufacturers' values vary; you can enter your catalogue values under Settings → Advanced.

Does the app need an internet connection?

No. All calculations and PDF reports work offline.

Is the app free?

Yes, completely free, with no ads and no in-app purchases.

I found a bug or have a suggestion.

Please write to us — feedback from engineers in the field shapes the next updates.

System requirements

Contact

Questions, bug reports and suggestions:

fatih@selvi.org