Fan Laws Calculator
New CFM, static pressure and power when fan speed changes — the air-side affinity laws.
20% more pulley speed = 73% more motor load — belt-drive 'speed-ups' burn out motors more often than they fix airflow problems.
Formula
Fan Laws Calculator is a free fan laws 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 Fan Laws Calculator
New CFM, static pressure and power when fan speed changes — the air-side affinity laws. The calculation implements Q∝N; SP∝N²; P∝N³ (AMCA 201 — fans and systems). 20% more pulley speed = 73% more motor load — belt-drive 'speed-ups' burn out motors more often than they fix airflow problems.
How to use Fan Laws Calculator
- 1Enter Airflow at N₁ in L/s.
- 2Enter Static pressure at N₁ in Pa.
- 3Enter Power at N₁ in kW.
- 4Enter Speed N₁ in rpm.
- 5Read New airflow, New static pressure, New power instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Fan Laws Calculator?
- ✓Implements the standard formula — Q∝N; SP∝N²; P∝N³
- ✓Reference cited on-page: AMCA 201 — fans and systems
- ✓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 Fan Laws Calculator use?+
It computes Q∝N; SP∝N²; P∝N³, per AMCA 201 — fans and systems. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
20% more pulley speed = 73% more motor load — belt-drive 'speed-ups' burn out motors more often than they fix airflow problems.
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 Fan Laws 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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