DuctWheel - HVAC Duct Sizer

New: stock sizes up and down, and a Check tab that tells you if an existing duct can carry the airflow. Real equal-friction duct physics, not a guessed chart.

DuctWheel sizes HVAC ductwork the way a mechanical designer would — by solving the actual duct friction physics, not by eyeballing a chart.

Enter your airflow (CFM) and a target friction rate, and DuctWheel solves for the round duct diameter using the Darcy-Weisbach equation with a Swamee-Jain friction-factor approximation (the same physics behind the SMACNA/ASHRAE duct friction charts). Need a rectangular duct instead? Convert between round and rectangular sizes using the standard ASHRAE equal-friction equivalent-diameter formula, in either direction.

Need to know what to actually order? DuctWheel shows the next stock round size up and down from the exact diameter, with the velocity and friction rate each one really gives, so you can see which meets your target.

Already have a duct in place? The Check tab tells you whether an existing round or rectangular duct can carry the airflow: velocity, friction rate, a verdict against your design friction rate, and the most airflow it can carry at that rate.

Why DuctWheel:

• Real duct physics (Darcy-Weisbach + Swamee-Jain), not a static lookup chart
• Next stock size up and down, with velocity and friction for each
• Check an existing duct: will it carry the airflow, and what is its capacity?
• Rectangular results show the aspect ratio and warn past SMACNA's 4:1 guidance
• Round-to-rectangular and rectangular-to-round conversion
• Galvanized and flex duct roughness presets, or enter your own
• Velocity flagged automatically when it's high enough to cause noise
• Save calculations to compare runs and jobs
• Works completely offline - no account, no ads

Reference tool note: this app is a design aid using standard published duct-friction methodology. Always check results against your project specs, local code, or a licensed mechanical engineer for anything code-critical.

One-time purchase, no subscription. No data collected.