Ductulator
The Ductulator is an interactive tool for sizing ductwork based on airflow and design parameters.
Duct Sizing Basics
Section titled “Duct Sizing Basics”Key Parameters
Section titled “Key Parameters”Airflow (CFM or L/s)
Section titled “Airflow (CFM or L/s)”The volume of air flowing through the duct.
Velocity (FPM or m/s)
Section titled “Velocity (FPM or m/s)”The speed of air in the duct. Higher velocity means:
- Smaller duct size
- More noise
- Higher pressure drop
Friction Rate
Section titled “Friction Rate”Pressure drop per unit length (in. wg/100 ft or Pa/m).
Duct Size
Section titled “Duct Size”Resulting dimensions:
- Round: diameter
- Rectangular: width × height
Using the Ductulator
Section titled “Using the Ductulator”Inputs
Section titled “Inputs”Enter your design constraints:
- Flow Rate — the volume of air moving through the duct (CFM or L/s)
- Max Velocity — the highest air velocity to allow (FPM or m/s; defaults to 1200 FPM)
- Max Pressure Drop — the highest friction rate to allow per unit length (in. wg/100 ft or Pa/m; defaults to 0.1)
- Max Height — caps the duct height so the result fits the available depth
- Liner Thickness — internal acoustic liner that reduces the clear airflow area
- Shape — Round or Rectangle
- Sizing Increment — the step the tool uses when generating candidate sizes (defaults to 2 in)
How sizing works
Section titled “How sizing works”The Ductulator generates candidate sizes at your sizing increment and selects the smallest one that stays within both the max velocity and the max pressure drop, while respecting the max height. There is no separate “velocity” or “equal-friction” mode — the tool satisfies every constraint at once.
To override the result, type a dimension directly:
- Round — set the Diameter; clear it to fall back to the calculated value
- Rectangle — set the Height and/or Width; each field shows the calculated value as a default you can reset to
Results
Section titled “Results”The results update live as you change inputs:
- A scaled cross-section preview of the duct (and its liner, when present)
- Pressure Drop — friction rate at the current flow and size
- Velocity — air velocity at the current flow and size
- Area — clear airflow area of the duct
Design Guidelines
Section titled “Design Guidelines”Velocity Limits
Section titled “Velocity Limits”| Application | Max Velocity |
|---|---|
| Main ducts | 2000 FPM |
| Branch ducts | 1200 FPM |
| Noise-sensitive | 800 FPM |
| Residential | 600 FPM |
Friction Limits
Section titled “Friction Limits”| Application | Friction Rate |
|---|---|
| Low velocity | 0.05 in/100 ft |
| Medium velocity | 0.10 in/100 ft |
| High velocity | 0.20 in/100 ft |
Aspect Ratio
Section titled “Aspect Ratio”For rectangular ducts:
- Keep aspect ratio < 4:1
- 1:1 to 2:1 is optimal
- Higher ratios increase friction
Practical Tips
Section titled “Practical Tips”Round vs. Rectangular
Section titled “Round vs. Rectangular”Round ducts have:
- Lower friction for same airflow
- Less material for same capacity
- Better sealing
- May not fit in tight spaces
Equivalent Diameter
Section titled “Equivalent Diameter”Compare rectangular to round:
- Same airflow and friction
- Use for mixed systems
- Verify with friction chart
Real-World Adjustments
Section titled “Real-World Adjustments”Consider:
- Actual available sizes
- Fitting losses
- Installation constraints
- Insulation thickness