Dust collection CFM calculator

Add up the CFM requirements of the machines that run at the same time, not every machine in the shop. A typical table saw wants around 350 CFM, a planer around 500, and a CNC router 800 or more. A one-person shop where only one machine runs at a time can size for its hungriest machine; a production floor sizes for the worst-case combination, plus 20 to 30% headroom.

Roughly 3,500 to 4,500 feet per minute in the duct. Below about 3,500 FPM, wood chips and dust fall out of the airstream and pile up in horizontal runs until the duct chokes. Much above 4,500 FPM, you pay a penalty in static pressure, noise, and duct wear without collecting any better.

The size that carries your airflow inside that velocity window. At 4,000 FPM, a 5-inch duct carries about 545 CFM, a 6-inch about 785, a 7-inch about 1,070, and an 8-inch about 1,400. Use the calculator's duct check to test any combination, and remember branches to single machines are sized to that machine, while the main is sized to the total.

The usual suspects, in order: clogged or loaded filters, too many open blast gates dropping the velocity everywhere, long runs of corrugated flex hose (which has two to three times the resistance of smooth pipe), leaks at joints, an undersized main, or a collector whose advertised CFM was measured with no duct attached. Real systems lose a lot to static pressure.

Both. Every foot of pipe, every elbow, and every flex section adds static pressure that the collector must overcome, and its delivered CFM drops as resistance rises. Keep runs short and straight, use long-radius elbows, keep flex hose to the last few feet at the machine, and check the collector's fan curve rather than its headline CFM.

Small hobby systems sometimes do, with grounding wire to control static. For a business, smooth-wall metal duct is the standard: it handles the airflow better, it's groundable, and commercial shops need to meet combustible dust requirements (NFPA standards and local fire code) that PVC systems generally don't. When in doubt, ask your insurer what they expect to see.

The visible chips are a housekeeping problem; the invisible dust under 10 microns is the health problem, and it's exactly what cheap filters pass straight back into the shop air. Look at the filtration rating of the collector, not just its CFM, and for production environments consider properly rated filter media or HEPA-class filtration and ambient air cleanup.

When multiple machines run at once, when you're adding a CNC router or wide belt sander, or when fire code and insurance are involved. An engineered system balances duct sizes branch by branch so every machine sees the right velocity. That's exactly the work we do with Nederman industrial dust collection.