HVAC Duct Flow
Fast answers for everyday duct and grille sizing checks. Size rectangular and round ducts, grilles and diffusers in one practical tool for the office or the field.
App Screens
Ducts, grilles and diffusers in one app
Duct and grille sizing in one app
Rectangular and round ducts, grilles and diffusers: velocity, pressure loss and throw.
Duct size in seconds
Turn the airflow dial: velocity, friction and the recommended size update live.
Equal friction, done right
Round spiral ducts sized to standard diameters by Pa/m or velocity.
Grilles and diffusers
8 types with velocity, pressure drop and throw.
Rectangular ↔ round
Find the equivalent diameter of any a×b duct.
Your standards, your limits
Metric or imperial units, materials, air conditions and velocity limits.
Features
One practical tool for the office or the field
Duct Sizing
Size rectangular and round (spiral) ducts by constant velocity or equal friction.
Duct Check
Check velocity, friction loss (Pa/m) and velocity pressure for any duct size.
Equivalent Diameter
Convert a rectangular a×b duct to its equivalent round diameter, and back.
Grilles and Diffusers
Size 8 grille and diffuser types with velocity, pressure drop and throw.
Real Conditions and Limits
Duct material roughness, air temperature and altitude are taken into account. Velocity warnings follow residential, office and industrial limits that you can tighten in Settings.
PDF, Units and Offline
Share one-page PDF reports, switch between SI and IP units, and use the app offline on iPhone and iPad, in 15 languages.
Calculation Method
Calculations based on ASHRAE Fundamentals
ASHRAE Fundamentals
Calculations follow ASHRAE Fundamentals: Darcy–Weisbach with the Colebrook equation.
Material, Temperature and Altitude
Duct material roughness, air temperature and altitude are taken into account.
Velocity Warnings
Warnings follow residential, office and industrial velocity limits, which you can tighten in Settings.
How To Use It
From airflow to duct size in four steps
Set the Airflow
Turn the airflow dial or type an exact value.
Choose a Method
Pick constant velocity or equal friction for rectangular or round (spiral) ducts.
Review the Results
Velocity, friction and the recommended size update live as you change the inputs.
Share the Report
Share the results as a one-page PDF report.
Frequently Asked Questions
HVAC Duct Flow sizes rectangular and round (spiral) ducts by constant velocity or equal friction, checks velocity, friction loss (Pa/m) and velocity pressure for any duct size, converts a rectangular a×b duct to its equivalent round diameter and back, and sizes 8 grille and diffuser types with velocity, pressure drop and throw.
Calculations follow ASHRAE Fundamentals: Darcy–Weisbach with the Colebrook equation. Duct material roughness, air temperature and altitude are taken into account.
Turn the airflow dial or type an exact value, choose constant velocity or equal friction, and review the results as they update live: velocity, friction and the recommended size. Velocity warnings follow residential, office and industrial limits that you can tighten in Settings.
The app covers 8 grille and diffuser types and gives velocity, pressure drop and throw for each.
Yes. The app works offline on iPhone and iPad running iOS 17.0 or later, in 15 languages. You can switch between SI and IP units and share one-page PDF reports.
Yes. The app is completely free, with no ads and no data collection.
Results are for guidance; the responsibility for design and installation remains with the engineer.
Download Now
Get HVAC Duct Flow free on the App Store and make your next duct calculation easier.