Ductsmith

About

Ductsmith sizes HVAC ducts on your iPhone. Type the airflow, pick equal friction or velocity, and get the round size plus every rectangular and flat oval option that carries the same air.

Size A Duct

Exact diameter, the nominal round sizes either side with their real friction and velocity, rectangular sizes for each height with aspect ratio, and flat oval sizes. A live drawing shows the section with its dimensions.

Check Any Size

Type any round, rectangular or oval size, even an odd one from the job. See velocity, friction loss, velocity pressure, Reynolds number and equivalent diameter. Or work backwards: how much air does this duct carry at your friction rate or velocity limit?

Add Up A Run

Build a run from straight sections and fittings. Elbows, entrances, takeoffs, dampers, expansions and contractions use editable loss coefficients. Add fixed drops for filters, coils and grilles. Ductsmith totals the pressure drop and exports a clean PDF or CSV.

Flex Duct, As Installed

Set how much a flex duct is compressed and friction is corrected with a published laboratory model, so a sagging run is not sized as if it were pulled tight.

Real Air

Air temperature and altitude change density and viscosity, and every result follows. The Air tab gives humidity ratio, dew point, wet bulb, enthalpy and specific volume, mixes two air streams and turns a sensible load into airflow.

Show The Math

Every result opens to the formulas and inputs behind it: Darcy-Weisbach, Colebrook, Huebscher. No black box.

Imperial Or Metric

CFM, L/s or m3/h. Inches or millimetres. in.wg per 100 ft or Pa/m. Switch any time.

Siri And Shortcuts

"Size a duct in Ductsmith" answers with a nominal size right in Siri or Shortcuts.

One Purchase, No Signal Needed

Buy it once. It sizes ducts in a basement or on a roof with no connection, and your runs stay on your iPhone.

Ductsmith is a calculation aid. Check results against your local code and the design of the system.