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Air Flow — Fan Laws
Air Flow tool step 2 — Fan affinity laws for speed / flow / pressure / power.
- Use when changing RPM or estimating new CFM (or L/s), SP, or BHP from known conditions. Open this step with Next in the top bar (no step dropdown).
- This step (and Settings / RefCalc duct) uses the CFM / L/s toggle. Air Flow step 1 shows both CFM and L/s as fields instead. Laws still run on CFM internally.
- Fan Law 1: CFM ∝ RPM. Law 2: SP ∝ RPM². Law 3: BHP ∝ RPM³. Assumes constant system resistance and air density (idealized). The tool’s Reference mode shows the same three laws.
- Field estimates only — real fans deviate with density, system effect, and selection.
Disclaimer: Field guide for technicians — not a substitute for nameplate data or local Code.