Fan Blade & Blower Wheel Calculator
Calculate airflow output, find replacement fan blades and blower wheels, and check if an on-hand part can substitute for the original. Enter what you know — the calculator does the rest.
Fan Blade Specifications
Results
Enter your fan blade specifications and click Calculate to estimate airflow and motor requirements.
Blower Wheel Specifications
Results
Enter blower wheel specifications and click Calculate to estimate airflow.
Compatibility Assessment
Tell Me More About Fan Blades & Blower Wheels
How they work, fan affinity laws, substitution rules, and safety
How Propeller Fan Blades Work
Axial fans push air parallel to the shaft. Condenser fans and exhaust fans are the most common HVAC examples. The blade pitch angle determines how much air each revolution moves — a steeper pitch means more air per revolution, but also more motor torque required. More blades add airflow and smooth out pulsation, but increase drag. The motor must be able to handle the resulting load across the operating temperature range of the installation.
How Blower Wheels Work
Centrifugal (squirrel cage) fans accelerate air outward radially and discharge it at 90 degrees from the intake. Air handlers, furnaces, and fan coil units use blower wheels. The size is specified as Diameter x Width (e.g. 10x8 means 10" diameter, 8" wide). Double-inlet wheels pull air from both sides and produce roughly double the CFM. Blower wheels are sensitive to wheel cleanliness — even a small buildup on the blades reduces airflow significantly.
The Fan Affinity Laws
The fan affinity laws govern how fan performance scales with speed. CFM is proportional to RPM (double the speed, double the airflow). Static pressure rises with RPM squared. Power (horsepower) rises with RPM cubed — this is the critical one. A 10% increase in fan speed requires 33% more motor horsepower. This is why substituting a blade with more aggressive pitch can cause motor overload even when the RPM is unchanged: more pitch at the same RPM produces more CFM, and the motor must work harder to maintain that speed.
Can a Different Blade Count Work?
Yes, if the resulting CFM is close to the original. A 4-blade at higher pitch can replace a 5-blade at lower pitch and produce similar airflow. The key constraints are bore size (must be exact), diameter (must fit the shroud), and rotation direction. The final test is always motor amp draw: after any substitution, run the system and measure amps with a clamp meter against the nameplate FLA. If amps exceed the FLA, the blade is too aggressive for that motor.
Constraints That Cannot Change
Bore size must match the motor shaft exactly — adapters and shims are unreliable and can cause blade detachment at speed. Diameter cannot exceed the shroud opening (blade must clear by at least 1/4" all around). Rotation direction must match the motor and the designed airflow direction through the coil. These three constraints are non-negotiable regardless of how close the CFM estimate appears.
Safety
Always disconnect and lockout/tagout power before working on any fan assembly. Verify the blade is fully seated and the set screw is torqued before energizing. Check blade clearance to the shroud by rotating the blade by hand before energizing. After any substitution, run the system and check motor amp draw on the highest speed setting. If you smell burning, see sparking, or the motor trips, shut down immediately and investigate before re-energizing.
Common Fan Blade Sizes — Quick Reference
| Diameter | Common Blades | Common Pitch | Typical RPM | Application |
|---|---|---|---|---|
| 10" | 3, 4, 5 | 27–33 deg | 1725 | Small PTAC, window units |
| 14" | 3, 4 | 25–30 deg | 1725 | Small condensers |
| 16" | 3, 4 | 25–30 deg | 1140–1725 | Residential condensers |
| 18" | 3, 4 | 24–27 deg | 1075–1140 | Residential condensers |
| 20" | 3, 4 | 24–27 deg | 1075–1140 | Residential condensers |
| 22" | 3, 4 | 24–27 deg | 825–1140 | Large residential / light commercial |
| 24" | 3, 4 | 24–27 deg | 825–1075 | Light commercial |
| 26" | 3, 4, 5 | 24–27 deg | 825–1075 | Commercial |
| 30" | 3, 4, 5 | 24–27 deg | 825–1075 | Large commercial |
Common Blower Wheel Sizes
| Size (DxW) | Bore | Typical RPM | Approx. Tonnage | Application |
|---|---|---|---|---|
| 9x6 | 1/2" | 1000–1200 | 1.5–2 ton | Small residential |
| 9x8 | 1/2" | 1000–1200 | 2 ton | Residential |
| 10x6 | 1/2" | 1000–1200 | 2–2.5 ton | Residential |
| 10x8 | 1/2" | 1000–1200 | 2.5–3 ton | Residential |
| 10x10 | 1/2" | 1000–1200 | 3–3.5 ton | Residential |
| 11x10 | 1/2" | 900–1100 | 3.5–4 ton | Residential |
| 12x10 | 1/2"–5/8" | 900–1100 | 4–5 ton | Residential / light commercial |
| 12x12 | 5/8" | 800–1000 | 5+ ton | Commercial |
| 15x15 | 3/4" | 600–800 | 7.5–10 ton | Commercial |