Advanced Fan Selection Calculator

Calculator Input

Airflow

Airflow Unit

Static Pressure

Pressure Unit

Fan Efficiency (%)

Motor Efficiency (%)

Safety Factor

System Effect Factor

Air Temperature (°C)

Altitude (m)

Operating Hours / Year

Load Factor (%)

Energy Cost per kWh

Preferred Fan Speed (RPM)

Duct Diameter (mm) - Optional

Performance Curve

The chart compares a quadratic system curve with a representative candidate fan curve. The marked point is the required catalog selection duty.

Example Data Table

Airflow	Static Pressure	Fan Efficiency	Motor Efficiency	Altitude	Temperature	Recommended Fan	Motor Size	Annual Energy
18,000 m³/h	900 Pa	70%	92%	250 m	30°C	Backward-Curved Centrifugal Fan	11 kW	20,580 kWh
9,500 CFM	3.2 in. w.g.	68%	91%	0 m	20°C	Mixed Flow / Inline Centrifugal Fan	7.5 kW	14,950 kWh
4.8 m³/s	450 Pa	72%	93%	1200 m	25°C	Axial Fan	4.0 kW	8,930 kWh

Formula Used

1) Airflow Conversion
Q (m³/s) = entered airflow converted from m³/h, CFM, or L/s.

2) Air Density
ρ = P / (R × T)
P uses altitude-corrected barometric pressure. T is absolute temperature in Kelvin.

3) Corrected Duty Pressure
ΔP_duty = static pressure × safety factor × system effect factor

4) Catalog Selection Pressure
ΔP_catalog = ΔP_duty / density ratio

5) Air Power
Air Power = Q × ΔP

6) Shaft Power
Shaft Power = Air Power / fan efficiency

7) Motor Input
Motor Input = Shaft Power / motor efficiency

8) Annual Energy
Annual Energy = Motor Input (kW) × operating hours × load factor

9) Impeller Diameter Estimate
D = (60 × tip speed) / (π × RPM)

These equations support preliminary engineering selection. Final fan choice should always be checked against a real manufacturer performance table, sound data, and motor service factor.

How to Use This Calculator

Enter the required airflow and choose the correct airflow unit.
Enter the design static pressure and its pressure unit.
Add fan efficiency, motor efficiency, safety factor, and system effect factor.
Enter site temperature and altitude for density correction.
Add yearly operating hours, load factor, and energy cost to estimate running cost.
Enter preferred RPM to estimate impeller diameter.
Optionally add duct diameter to check duct velocity.
Press the calculate button to view the result section above the form, the graph, and export options.

Frequently Asked Questions

1) What does this calculator actually select?

It gives a preliminary fan recommendation based on airflow, pressure, density, power, and operating conditions. It estimates fan type, motor size, and an approximate impeller diameter for early engineering decisions.

2) Why is density correction important?

Air density changes with altitude and temperature. Lower density reduces fan pressure at the same speed. Correcting pressure helps you compare your duty point with catalog ratings at standard air.

3) Why include a safety factor?

Safety factor covers design uncertainty, future fouling, and minor resistance growth. It prevents under-selection and gives a more practical duty point for real installations.

4) What is the system effect factor?

System effect accounts for losses from poor inlet conditions, abrupt transitions, elbows near the fan, and uneven flow. Ignoring it may cause the installed fan to miss the design point.

5) Is the impeller diameter exact?

No. It is an engineering estimate based on pressure coefficient and selected RPM. Always verify wheel size with the manufacturer’s fan curve, arrangement, and blade design data.

6) How is annual energy cost calculated?

The calculator multiplies motor input power by yearly operating hours and load factor. It then multiplies the result by your energy price per kilowatt-hour.

7) Can I use this for HVAC and industrial exhaust?

Yes. It works for general ventilation, ducted HVAC, process air, and exhaust screening. Final selection still needs material compatibility, temperature rating, and sound review.

8) Why does the graph matter?

The graph helps you visualize the duty point against a representative fan curve and system curve. It shows whether the chosen fan family fits the expected operating range.