Calculator Inputs
This page keeps a white theme and a stacked page structure, while the input grid changes to three columns on large screens, two on medium, and one on mobile.
Example Data Table
The table below shows a realistic sample case using a single 24 × 24 inch filter at 2,200 CFM.
| Airflow | Filter Size | Parallel Filters | Face Velocity | Clean Drop | Loaded Drop | Design Drop | Fan Power |
|---|---|---|---|---|---|---|---|
| 2,200 CFM | 24 × 24 in | 1 | 2.79 m/s | 109.11 Pa | 158.11 Pa | 173.92 Pa | 264.96 W |
| 1,600 CFM | 24 × 24 in | 1 | 2.03 m/s | 74.19 Pa | 123.19 Pa | 135.51 Pa | 149.50 W |
| 2,200 CFM | 24 × 24 in | 2 | 1.39 m/s | 50.50 Pa | 99.50 Pa | 109.45 Pa | 166.65 W |
Formula Used
This calculator uses a Darcy–Forchheimer style clean-media model, then adds frame loss, dust loading resistance, and a design safety allowance.
Where:
- μ = dynamic viscosity of air
- L = media thickness
- K = media permeability
- ρ = air density
- Cf = inertial coefficient
- η = fan efficiency as a decimal fraction
How to Use This Calculator
- Enter the airflow and choose the correct airflow unit.
- Type the filter width and height, then select the dimension unit.
- Set how many filters operate in parallel.
- Enter media thickness, air density, viscosity, permeability, and inertial coefficient.
- Add dust loading, dust resistance slope, and frame loss.
- Enter fan efficiency, safety factor, and replacement limit.
- Press Calculate Pressure Drop.
- Review the result section above the form, inspect the graph, and export the summary as CSV or PDF.
Frequently Asked Questions
1) What does air filter pressure drop mean?
Pressure drop is the resistance the filter adds to airflow. Higher resistance means the fan works harder, energy use rises, and airflow may fall if the system cannot overcome the added static pressure.
2) Why is face velocity important?
Face velocity strongly affects pressure loss. As velocity increases, viscous and inertial losses rise. That means small filters at high airflow usually create much higher pressure drop than larger filters handling the same airflow.
3) What permeability value should I use?
Use the tested media permeability from laboratory data, supplier data, or internal design standards. If exact data is unavailable, begin with a reasonable estimate, then calibrate the result against measured clean-filter pressure drop.
4) Why does loaded pressure drop rise over time?
Dust accumulation blocks pores and adds flow resistance. As the loading layer thickens, the filter needs more pressure to move the same airflow. That is why final resistance limits matter in maintenance planning.
5) How do parallel filters affect the result?
Parallel filters increase total face area. More area lowers face velocity, which usually reduces both clean and loaded pressure drop. This is one of the most effective ways to cut resistance in a filter bank.
6) What is the replacement limit used for?
The replacement limit is the maximum acceptable operating pressure drop before the filter should be changed. It helps compare present resistance against maintenance criteria and supports fan sizing and operating decisions.
7) Is the fan power result exact?
No. It is an engineering estimate based on airflow, pressure drop, and fan efficiency. Real systems also depend on motor efficiency, drive losses, control strategy, and the full duct system resistance curve.
8) Which units does this calculator support?
Airflow can be entered in CFM, m³/s, m³/h, or L/s. Dimensions support millimeters, centimeters, meters, and inches. Internally, the calculator converts everything to SI units for the actual computation.