VALICALC · ENGINEERING WORKFLOW
HVAC duct airflow and size check
Connect room airflow, a stated velocity or friction criterion, and round/rectangular duct dimensions with clear equal-area and equivalent-diameter distinctions.
Start this workflowWhat do I need to know first?
- Required airflow from the design or a stated ACH scenario
- Inside duct dimensions and preferred shape
- Velocity/friction criterion, straight-run length and air properties
Goal and model boundaries
Compare duct geometry at a known airflow while keeping ventilation demand and system pressure design explicit.
- ACH scenarios are calculations, not occupancy-specific ventilation recommendations.
- Straight-duct loss is not the full fitting, terminal and fan system pressure budget.
State the airflow basis
Enter room dimensions and the known airflow or target ACH scenario.
ACH = Q × 3600 / room volume when Q is in m³/s.
- Expected output
- A consistent airflow and air-change scenario.
- Next step
- Use the required airflow from the applicable design, then choose a duct criterion.
Compare a velocity scenario
Review several velocities at the same airflow.
Area = Q/v; reference scenarios do not prescribe an acceptable noise or ventilation level.
- Expected output
- Candidate area and equal-area round diameter.
- Next step
- Use a stated velocity or friction criterion in Duct Size.
Solve and cross-check duct geometry
Choose round or rectangular and the governing criterion.
The shared solver calculates size or flow using the selected continuity/friction model.
- Expected output
- Duct dimensions, mean velocity and straight-run friction estimate.
- Next step
- Check real fitting losses, acoustic requirements and fan performance in the project design.
Units and context
- CFM and m³/s measure volume flow; ACH additionally depends on room volume.
- Equal-area and equal-friction round diameters answer different questions.
Common mistakes to avoid
- Using a reference velocity scenario as a mandatory design limit
- Ignoring fittings and terminal losses
- Sizing from outside rather than inside duct dimensions