Duct Friction Loss Calculator
Who it's for: HVAC service technicians, balancers, and designers.
Calculator Inputs
Quick Summary
- Built for: HVAC service technicians, balancers, and designers.
- Key outputs: Total equivalent length, Estimated friction rate, and more.
- Use this page for early planning estimates before final code and manufacturer verification.
Inputs
- Total duct length (ft)
- Equivalent fitting length (ft)
- Duct diameter (in)
- Airflow (CFM)
Outputs
- Total equivalent length
- Estimated friction rate
- Pressure drop estimate
How this calculator estimates results
- Builds total equivalent length from straight duct plus fitting equivalent length.
- Calculates approximate air velocity from airflow and round-duct area.
- Uses a simplified heuristic to estimate loss per 100 ft and total pressure drop over the run.
Cross-check assumptions with Duct Size Calculator for a more complete planning workflow.
Common ranges and tips
- Long runs and small diameters can quickly increase estimated pressure losses.
- Use equivalent fitting length inputs consistently to compare design options.
- Confirm final static pressure with measured system data and manufacturer fan performance curves.
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FAQ
It is a way to represent fitting losses as additional straight duct length so total run resistance can be approximated quickly.
Real systems vary by duct roughness, leakage, transitions, and equipment behavior that are not fully modeled here.
Common options include larger duct diameter, shorter runs, smoother transitions, and reduced fitting losses.
Use it as planning guidance only and verify final performance with measured static pressure and balancing data.
Disclaimer: Use results for planning only. Final design and installation decisions must follow local code and manufacturer documentation.
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