Airflow sizingCleaner, safer shopDuct + loss aware
Dust Collection CFM Calculator
Estimate the airflow you need to keep chips moving and fine dust under control. Size for real-world pressure losses, not marketing numbers.
Capture rules of thumb
- Aim for strong capture at the source. Hood design matters.
- Keep mains smooth and short. Flex hose is the silent airflow tax.
- Seal leaks. They don’t look dramatic, they just quietly delete CFM.
Pro move: size for the worst-case run (longest duct + most fittings), not your easiest machine.
Dust Collection CFM + Static Pressure (Pro)
Uses Total Effective Length + friction-loss math for realistic fan requirements.
Nearest port: 4" → 400 CFM
Friction multiplier: x1
Impacts TEL via elbow equivalent length.
Guideline airflow
4 port → 400 CFM
You can switch to “Manual” or “Target velocity” for precise designs.
Fittings (TEL)
Straight: 20 ft • Fittings equiv: 40 ft • TEL: 60 ft
Warnings
- Duct velocity is low (2037 FPM). Risk of settling/clogs in horizontal runs.
Required Airflow
400 CFM
Port guideline based on nearest port size: 4" → 400 CFM
Duct Velocity
2037 FPM
Port velocity: 4584 FPM
Total Static Pressure
1.46 in. w.g.
Friction: 0.71 in. w.g. + Add-ons: 0.75 in. w.g.
Fan requirement (verify on fan curve)
400 CFM @ ~1.46 in. w.g.
Dust Collection Requirement Report
Airflow basis: Port guideline based on nearest port size: 4" → 400 CFM
Required airflow: 400 CFM
Diameters:
- Port: 4"
- Duct: 6"
Velocities:
- Duct velocity: 2037 FPM
- Port velocity: 4584 FPM
Effective length (TEL):
- Straight duct: 20 ft
- Fittings equivalent: 40 ft
- Total effective length: 60 ft
Losses (in. w.g.):
- Friction loss: 0.71 in. w.g. (material x1)
- Hood loss: 0.75 in. w.g.
- Cyclone loss: 0 in. w.g.
- Filter loss: 0 in. w.g.
- Misc loss: 0 in. w.g.
TOTAL static pressure: 1.46 in. w.g.
Fan requirement (check fan curve):
400 CFM @ ~1.46 in. w.g.
Formula
CFM ≈ Duct Area × Transport Velocity
Then account for real losses from duct length, fittings, filters, and separators (static pressure).
How to use
- Pick your tool port and a target transport velocity (often ~4000 FPM for chips).
- Estimate your duct run: diameter, length, elbows, flex hose, filters, separators.
- Choose a collector that delivers the target CFM at your expected static pressure.
FAQs
Is bigger duct always better?
Not always. Bigger duct can reduce velocity, which can let chips drop out. Size for both adequate CFM and enough velocity to keep material moving.
What is static pressure?
It’s the resistance your blower must overcome (duct friction, elbows, filters, cyclone, etc.). Real performance is “CFM at static pressure”, not the no-hose marketing number.
Why does flex hose hurt so much?
The ridges create turbulence and add a lot of friction loss. Keep flex short, use smooth pipe for the bulk of the run.