Equal Friction Duct Sizing Calculator
Size a duct to a constant friction rate (Pa/m) — the standard low-rise design method.
Equal friction keeps every metre of duct equally 'expensive' in pressure. After sizing, check the velocity verdicts — long index runs may still need a fan-pressure check.
Formula
Equal Friction Duct Sizing Calculator is a free equal friction method for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Equal Friction Duct Sizing Calculator
Size a duct to a constant friction rate (Pa/m) — the standard low-rise design method. The calculation implements ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, SI) — solved for D (ASHRAE Handbook — Fundamentals, duct friction chart). Equal friction keeps every metre of duct equally 'expensive' in pressure. After sizing, check the velocity verdicts — long index runs may still need a fan-pressure check.
How to use Equal Friction Duct Sizing Calculator
- 1Enter Airflow in L/s.
- 2Enter Friction rate in Pa/m (Supply 0.8–1.0 Pa/m · return 0.6).
- 3Read Duct Ø, Resulting velocity instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Equal Friction Duct Sizing Calculator?
- ✓Implements the standard formula — ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, SI) — solved for D
- ✓Reference cited on-page: ASHRAE Handbook — Fundamentals, duct friction chart
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Equal Friction Duct Sizing Calculator use?+
It computes ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, SI) — solved for D, per ASHRAE Handbook — Fundamentals, duct friction chart. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Equal friction keeps every metre of duct equally 'expensive' in pressure. After sizing, check the velocity verdicts — long index runs may still need a fan-pressure check.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Equal Friction Duct Sizing Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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