Airflow
Usually shown as m³/h, m³/s or CFM. It is the required air volume delivered by the fan.
Pressure
Confirm whether the curve and project requirement use static pressure or total pressure.
Power
Absorbed power at the operating point is the basis for motor power and safety margin.
Efficiency
A better operating range usually means more stable operation and lower power waste.
What Is a Fan Performance Curve?
A fan performance curve is a chart showing how a fan performs at a fixed speed and impeller size. It usually includes airflow, pressure, absorbed power, efficiency and sometimes noise.
For industrial fan selection, the curve is more useful than model name alone. Two fans with similar motor power may have different airflow and pressure ranges. The correct fan must be checked at the real operating point.
Read the airflow requirement
m³/h or CFM must match the process demand.
Confirm pressure basis
Static pressure and total pressure cannot be mixed.
Check power demand
Motor power should cover absorbed power plus margin.
Confirm the operating point
The fan must meet airflow and pressure at the same point.
Main Values on a Fan Curve
Different manufacturers may use different curve formats, but the main values are usually similar. Before comparing fan models, always confirm the units and whether the pressure value is static pressure or total pressure.
| Curve Value | Common Unit | What It Means | Selection Note |
|---|---|---|---|
| Airflow | m³/h, m³/s, CFM | Volume of air delivered | Must match the required process airflow. |
| Pressure | Pa, mmAq, in.wg | Pressure generated by the fan | Confirm static pressure or total pressure. |
| Speed | rpm | Impeller rotating speed | Speed changes airflow, pressure and power. |
| Power | kW, HP | Absorbed power or motor direction | Motor must have proper margin. |
| Efficiency | % | Power-to-airflow conversion efficiency | Avoid working far away from the efficient range. |
Test Boundary and Performance Representation
A fan performance curve is useful only when the test boundary is clear. Before comparing airflow, pressure, power or efficiency, buyers should confirm what equipment is included in the published data.
Fan Only
The curve represents the fan body and impeller performance. Motor, belt, coupling, VFD and system accessories may not be included.
Fan with Inlet or Outlet Parts
Some test data may include inlet boxes, dampers, silencers, guards or outlet transitions. These parts can change pressure loss and efficiency.
Fan and Drive
For belt-driven or coupling-driven fans, transmission losses should be identified when power or efficiency values are used for energy comparison.
Wire-to-Air
Wire-to-air performance includes electrical input power. It is useful for energy review, but it must state the motor, controller and operating condition.
Static Efficiency, Total Efficiency and Wire-to-Air Efficiency
Efficiency values on fan curves are not always based on the same definition. Buyers should confirm whether the curve is showing static efficiency, total efficiency or a wider electrical-input efficiency boundary.
Fan Static Efficiency
Uses static pressure as the useful pressure output. It is commonly reviewed in duct resistance and industrial ventilation applications.
Fan Total Efficiency
Uses total pressure as the useful pressure output. It includes velocity-pressure effects and should not be mixed with static efficiency.
Wire-to-Air Efficiency
Compares useful air power with electrical input power. It can include motor, drive and controller losses depending on the stated boundary.
How to Compare Two Fan Curves Fairly
When two fan suppliers provide different curves, the buyer should not compare only the highest efficiency number or the installed motor power. Use the same duty point and the same performance boundary.
| Curve Review Item | What to Confirm | Why It Matters |
|---|---|---|
| Airflow | Same m³/h, m³/s or CFM | Efficiency changes across the curve, so the duty point must match. |
| Pressure | Static pressure or total pressure | Static and total pressure are different bases and should not be mixed. |
| Density | Temperature, altitude and gas condition | Air density affects pressure, power and correction of performance data. |
| Speed | RPM, frequency, pulley ratio or VFD setting | Speed changes airflow, pressure, power and noise level. |
| Power | Fan shaft power, motor output or electrical input | Different power boundaries cannot be compared directly. |
| Efficiency | Static efficiency, total efficiency or wire-to-air efficiency | The definition must be aligned before judging which fan is more efficient. |
Need to Compare Fan Efficiency for a US Project?
For US projects, curve comparison should also identify the test boundary, efficiency definition, power boundary, destination state and any project-specific FEI or energy-code requirement.
Read US Fan Efficiency Comparison GuideWhere the System Curve Meets the Fan Curve
The operating point is where the fan curve and the system resistance curve meet. It represents the actual airflow and pressure after the fan is installed.
If the duct becomes longer, the filter becomes loaded, or the damper is adjusted, the system curve changes. The fan may then work at a different airflow and pressure point.
Why Static Pressure, Total Pressure and Filter Resistance Matter
For dust collection fans, baghouse fans, boiler induced draft fans and long duct systems, the pressure value must include the real resistance network. Duct length, elbows, dampers, silencers, filters, baghouse loaded-filter pressure drop and outlet loss can all move the operating point.
Static Pressure
Used to overcome duct, filter and system resistance.
Total Pressure
Includes static pressure and velocity pressure.
Filter Resistance
Clean-filter and loaded-filter pressure drop should be reviewed separately.
System Curve
Resistance changes can reduce airflow even when the fan model remains unchanged.
Power Curve, Motor Selection and Speed Change
The power curve shows how much power the fan absorbs at different airflow points. Motor selection should be based on absorbed power at the operating point plus suitable margin. Fan speed changes also affect airflow, pressure and power, especially when comparing 50Hz, 60Hz or VFD operation.
Absorbed Power
Do not only look at installed motor power.
Motor Margin
Leave margin for real operation and load fluctuation.
RPM and Frequency
50Hz, 60Hz and VFD control can change fan speed and power.
Common Mistakes When Reading Fan Curves
Selecting by Maximum Airflow
Maximum airflow at low pressure is not the required operating point.
Ignoring Pressure Basis
Static pressure and total pressure should be checked correctly.
Forgetting Motor Power
A fan may meet airflow and pressure but require more power than expected.
Better Method
Read airflow, pressure, speed, power and efficiency together.
Data Required for Curve Review
Performance Data
- Required airflow and pressure
- Static pressure or total pressure basis
- Fan speed or motor pole requirement
- Required operating point and margin
Electrical Data
- Voltage and frequency
- Motor standard
- VFD or fixed-speed operation
- Motor power and control requirement
System Condition
- Working medium and temperature
- Dust and corrosion condition
- Duct layout and filter resistance
- Installation direction and outlet angle
Technical Guides You May Also Need
FAQ About Fan Performance Curves
Can I select a fan only by model number?
No. The fan model must be checked together with airflow, pressure, speed and motor power at the required operating point.
What is the most important point on a fan curve?
The operating point is most important. It shows the airflow and pressure where the fan actually works in the system.
Why are there two speeds on some fan curves?
Two speeds may represent different motor pole speeds, belt drive ratios or VFD operating conditions. The required speed should be confirmed before ordering.
Should the motor be selected by absorbed power or installed power?
Motor selection should consider absorbed power at the operating point plus a suitable safety margin. Installed power alone does not explain the full selection.
Should filter resistance be included on a dust collection fan curve review?
Yes. For baghouse or dust collector systems, duct resistance, filter resistance, loaded-filter pressure drop and outlet loss should be included when checking the required pressure.
What should I send if I do not understand the curve?
Send the curve drawing, required airflow, pressure, speed, voltage, frequency and working condition. QIYUE FAN can help review the fan selection direction.
Need Help Reading a Fan Curve?
Send your fan curve, airflow, pressure, fan speed, motor information and system condition. QIYUE FAN can help check the operating point, motor power and suitable fan direction for industrial ventilation, boiler draft, dust collection or workshop exhaust systems.
Send: Fan Curve | Airflow | Static / Total Pressure | Speed | Power | Medium | Temperature | Dust / Filter Resistance | Voltage | Frequency | Quantity