Fan Calculator
Estimate performance changes of the same fan when speed changes.
How to Use This Calculator
Enter baseline and new RPM
Speed change ratio determines flow, pressure, and power scaling.
Optionally enter baseline performance
Provide any combination of Q₁, P₁, H₁ to project the corresponding new values.
Interpret results
Affinities hold for the same fan at similar operating conditions and static system.
Formula
Q₂ = Q₁ · (N₂/N₁)
P₂ = P₁ · (N₂/N₁)^3
H₂ = H₁ · (N₂/N₁)^2
Where: N = fan rotational speed, Q = volumetric flow, P = pressure rise, H = shaft power.
Example: Increase speed by 25% → Q +25%, P +95%, H +56%.
About Fan Affinity Laws
Fan affinity laws relate performance to speed for geometrically similar conditions. They are useful for quick estimates but do not replace full system curve intersections.
- Valid for the same fan and fluid with modest changes.
- System resistance curve determines operating point; results are indicative.
Frequently Asked Questions
What about diameter changes?
These formulas assume the same fan diameter. Changing diameter requires similarity scaling.
Do units matter?
No, as long as Q₁, P₁, H₁ units are consistent between baseline and result.
System curve?
Real operating point is the intersection of fan curve and system curve; use manufacturer data for accuracy.