Calculator Inputs
Example Data Table
| Material | Duct (in) | Velocity (fpm) | Branches | Diversity | Safety | Result (CFM) |
|---|---|---|---|---|---|---|
| Concrete / silica dust | 6 | 4500 | 2 | 0.8 | 1.1 | ~1550 |
| Wood dust / sawdust | 4 | 4000 | 3 | 0.7 | 1.1 | ~900 |
| Welding fume | 3 | 2500 | 1 | 1.0 | 1.2 | ~120 |
Formula Used
How to Use This Calculator
- Select a dust type preset, then adjust velocities if needed.
- Enter duct diameter and number of active branches.
- Set diversity for expected simultaneous tool operation.
- Enable hood airflow when sizing local capture openings.
- Add duct length, elbows, and filter losses for pressure estimates.
- Press Calculate to view airflow, pressure, and power above.
- Download CSV or PDF for documentation and handover.
Technical Article
Airflow targets for common construction dust
Effective collection starts with the right airflow. This calculator uses transport velocity to keep particles moving inside ducts and optional capture velocity to pull dust into a hood opening. Typical transport targets range from 2500–4500 fpm, while capture targets often sit near 75–250 fpm depending on release energy, distance, and cross-drafts. Presets provide practical starting points for general dust, wood dust, silica-related dust, and local fume capture.
Branching and diversity in real jobsite setups
Multiple tools rarely run at full flow simultaneously. The diversity factor reduces the summed branch demand to match expected concurrent use, which can prevent oversizing and reduce operating cost. For example, three pickups with a 0.70 diversity assume roughly two tools are active most of the time. Add a safety factor to cover leakage, imperfect fittings, and future filter loading so the system still performs when conditions worsen.
Pressure losses and why they matter
Airflow alone does not select a fan; static pressure determines whether that airflow is achievable. This page estimates total pressure from equivalent duct length, friction loss per 100 ft, hood entry loss, separator loss, and filter pressure drop. Long runs and frequent elbows increase equivalent length, raising pressure demand. Using a loaded filter pressure drop yields more dependable sizing than a clean, new-filter value.
Power estimate for budget and generator planning
Fan power is estimated using airflow, total static pressure, and fan efficiency. Higher pressure systems can require disproportionately more power, especially when filters load or ducts are undersized. The calculator reports horsepower and kilowatts to support motor selection, generator capacity checks, and energy-cost comparisons between alternative duct sizes, layouts, and filter choices.
Interpreting results for equipment selection
Use the required CFM as a minimum target and compare it against dust collector fan curves at the calculated static pressure. If a fan cannot deliver the flow at that pressure, consider larger ducts, smoother routing, fewer elbows, or higher area filtration to reduce pressure. Document outputs with the CSV/PDF options to support submittals, commissioning notes, and maintenance planning for stable long-term performance.
FAQs
CFM is the airflow rate needed to move dust through ducts and into the collector. The tool combines duct branch airflow, optional hood airflow, and a safety factor to estimate a practical minimum target.
Use it when you have a defined hood opening or capture point at the source. It adds local capture demand to duct transport demand, which helps size systems for grinders, saws, or downdraft tables.
Pick a value that matches expected simultaneous tool use. 1.0 assumes all branches operate together. Values like 0.6–0.8 fit crews where only some pickups run at any moment.
Filters often dominate total static pressure. As filters load, pressure rises and airflow falls unless the fan has reserve capacity. Using a loaded filter drop improves reliability and reduces performance surprises.
They are planning estimates. Actual values depend on fittings, duct roughness, transitions, leaks, and fan curve data. Use results to compare options, then confirm final selection with manufacturer performance curves.
Compare the required CFM at the estimated static pressure against candidate dust collectors. If margins are tight, improve duct layout, increase duct size, reduce elbows, or lower filter resistance before buying equipment.