Support

Write to support@getondia.com. We answer every message, usually within a working day. If a number looks wrong, send the inputs and what you expected: we check it against the source.

How does it size a duct?

With the Darcy-Weisbach equation and the Colebrook friction factor, solved exactly, as in the ASHRAE Handbook, Fundamentals, chapter 21. That is the equation the printed friction chart is drawn from, so at standard air in galvanized duct they agree. Rectangles and flat ovals are matched by equal friction (Huebscher), not by equal area.

Why does it round up?

A duct one size over costs a little metal; a duct one size under costs airflow and noise. The app always gives the next stock size up and shows what the size below would run at.

What friction rate should I use?

Work it out in Design, Design friction rate: the blower's external static at the design airflow, minus the coil, filter, registers and dampers, over the longest supply plus return path. Below about 0.06 in. w.g. per 100 ft ducts get large; above about 0.18 they get fast.

Flex duct

Fully stretched flex uses ASHRAE's roughness of 0.003 ft. Compression multiplies the friction by factors measured at Lawrence Berkeley National Laboratory: about four times at 15 percent.

Units, languages and data

US or metric units, in Settings. English, Spanish and French. Everything works offline and stays on your device.

Soporte en español · Assistance en français

Escríbenos en español a support@getondia.com. Écrivez-nous en français à la même adresse.