Dust Collection Calculator

Dust Collection Calculator for woodshop duct runs. Enter your machine, duct, hose and fittings to see the static pressure, duct speed and airflow your collector can really deliver.

Sizing Shop Ducts With the Dust Collection Calculator

The Dust Collection Calculator checks one duct run from a woodworking machine back to your collector. It adds up the static pressure lost along the way, then estimates how much airflow your collector can really pull through that run.

It is meant for small-shop owners planning ductwork, and for anyone whose table saw still throws dust with the collector running. Run it for the longest or hungriest run in the shop, because that run decides whether the whole system works.

What the Machine Needs and Why the Duct Speed Matters

The machine presets come from the airflow chart in the Oneida Air Systems Ductwork Design and Installation Guide. It lists 400 to 600 CFM for a 10 to 16 in table saw and 700 to 800 CFM for an 18 to 20 in planer. The presets use the top of each range.

Chip collection and fine dust collection are different targets. Bill Pentz credits air engineers with 350 CFM for good chip collection and 1,000 CFM for fine dust at larger tools. The Fine Dust goal raises the machine airflow to that 1,000 CFM floor.

Airflow then has to move fast enough to carry the dust along the duct. Duct speed in FPM is the airflow in CFM divided by the duct's cross-section, with the diameter in inches.

$$V=\frac{Q}{\pi (D/24{)}^2}$$

Oneida puts woodworking ducts at 3,500 to 4,500 FPM in its airflow vs. pipe diameter guide. On the Bill Pentz ducting page, horizontal runs start building piles below about 2,800 FPM. Vertical runs need about 3,800 FPM to lift heavier chips.

The first card reports the speed in the main and in the drop at your target airflow. It judges the main against the 2,800 FPM horizontal figure and the drop against the 3,800 FPM vertical figure, and turns red if either falls short.

The default table saw run shows why a bigger main is not always better, since 600 CFM moves through a 6 in main at only 3,056 FPM. Oneida's older guide makes the same point, calling 5 in duct the small-shop sweet spot and warning that 6 in is too large for collectors moving 600 to 700 CFM.

How the Dust Collection Calculator Adds Up Static Pressure

Every part of the run steals some of the collector's pressure. The calculator uses the losses Oneida measured at 4,000 FPM in its static pressure guide, covering 3 to 8 in pipe, flex hose, 90 and 45 degree elbows and 45 degree wyes.

Your air rarely moves at exactly 4,000 FPM, so each value is scaled to your actual speed. Straight pipe and hose scale with speed to the 1.9 power, and fittings with speed squared.

$$\Delta P_{run}=L\cdot p_{4000}{\left(\frac{V}{4000}\right)}^{1.9}$$

$$\Delta P_{fitting}=n\cdot k_{4000}{\left(\frac{V}{4000}\right)}^2$$

The 1.9 exponent lines up with Oneida's own figures for 100 ft of 4 in pipe. Those rise from 0.65 in. at 100 CFM to 9.0 in. at 400 CFM, a slope of 1.9 at each doubling.

Two budget items are added on top. Oneida suggests allowing 2 in. of water gauge for hood and port entry at a typical machine, and another 2 in. for any cyclone in the run.

The default run totals 5.52 in. at 600 CFM, and 5 ft of 5 in flex hose is the single biggest duct loss at 1.35 in. That is more than the 6 ft of rigid drop pipe and the 20 ft main combined. Keeping hose short is the cheapest fix most shops have.

Where Your Collector Actually Lands

A collector does not deliver its rated CFM once it is connected to duct. The third card estimates the real flow by drawing a curve through the maker's free-air airflow and maximum static pressure, then finding where that curve crosses your run.

$$S{P}_{fan}=S{P}_{max}\left[1-{\left(\frac{Q}{Q_{free}}\right)}^2\right]$$

That curve shape is the calculator's own estimate, not a maker's published fan curve. For the Grizzly G1029Z2P, rated 1,550 CFM with 11 in. of maximum static pressure at zero flow, the default run meets the curve at about 745 CFM and 8.5 in.

Free-air ratings run high, and some makers say so. Laguna lists its C|Flux:1 at 1,314 CFM maximum airflow but only 900 CFM in a shop setting. If your collector's maker publishes a real fan curve, trust it over this estimate.

At 745 CFM, the main duct speed rises from 3,056 FPM to about 3,797 FPM, back inside Oneida's range. That is why the alert calls this run below the usual speed rather than failing it.

Picking a Duct Size That Keeps Chips Moving

The fourth card works backward from your airflow to the main size that carries it at 4,000 FPM. It then rounds to standard sizes that keep the main at 3,500 FPM or more and the drop at 3,800 FPM or more.

$$D=24\sqrt{\frac{Q}{4000\pi }}$$

For 600 CFM, the exact size is 5.2 in, so the card suggests 5 in for both the main and the drop. The Airflow by Duct Size table shows the same thing from the other side, with 5 in pipe carrying 477 to 614 CFM across 3,500 to 4,500 FPM.

A separator adds its own floor. Oneida rates the Super Dust Deputy 4/5 for at least 350 actual CFM and the XL for at least 850, and the alert warns when your run falls under either.

Inputs run from 50 to 5,000 CFM of machine airflow, 3 to 16 in for the main and 2 to 8 in for the drop. Fitting counts must be whole numbers, and collector maximum static pressure must be 2 to 40 in. Losses assume sea-level air, and real results shift with filter loading, leaks and hood design.

Run Mistakes That Starve a Machine

Leaving other blast gates open is the most common one. Each open gate pulls air away from the machine you are using, which the Other Gates Open box accounts for.

Planning with the collector's advertised CFM is the second. As the third card shows, a run with real hose, elbows and a hood entry gets far less than the free-air number.

The third is necking a large main down to a small drop. Bill Pentz shows a 4 in drop on a 6 in main slowing the main to about 1,777 FPM, well under the 2,800 FPM needed to stop piles. If you are still placing machines, the Workshop Layout Calculator helps keep the hungriest ones close to the collector.

Dust Collector Questions From Real Shops

My tools have 4 in ports. Should I still run 5 or 6 in duct?

Oneida's advice is to run the largest duct you can, up to the size of the collector inlet, and reduce only at the tool. Duct larger than the collector inlet gains nothing because the inlet still limits the airflow.

The speed check still applies. A big main fed by a collector that only moves 600 CFM can drop below the speed that keeps chips moving, which is exactly what the first card flags.

How much airflow does a 2 HP dust collector really deliver?

It is usually far less than the label says. Bill Pentz says a typical 2 HP hobby collector with a 12 in impeller moves about 1,200 CFM at most, and that 4 in duct cuts it to around 450 CFM. A Sawmill Creek thread cites American Woodworker testing a 2 HP Oneida at 800 CFM at 8 in. of static pressure.

Oneida's own planer example makes the same case. A 6 in run to a 20 in planer needs 800 CFM at 8.4 in., while the same run in 4 in pipe delivers about half the airflow.

Is it better to use two 45 degree elbows instead of one 90?

Oneida's measurements show almost no difference between the two layouts. At 5 in, two 45 degree elbows lose 0.532 in. and one 90 loses 0.531 in. at 4,000 FPM.

Oneida recommends a single 90 where possible, because fewer joints mean fewer air leaks. A long-radius elbow, with a centerline radius at least 1.5 times the diameter, beats both.

Can I use PVC pipe for dust collection?

Many hobby shops do, but Oneida's guide argues for grounded metal. It quotes the 2002 edition of the NFPA standard for wood waste conveying, which says nonconductive ducts such as PVC shall not be permitted, and warns that static sparks can ignite fine wood dust.

The loss values here come from Oneida's tests on metal duct and fittings. PVC fittings are shaped differently, so treat the results as an approximation for a plastic system.

Does altitude change the static pressure in my ducts?

The ducts themselves are barely affected. Oneida says thinner air does not make duct losses worse, so a duct plan designed for a sea-level shop still works at altitude.

What changes is the collector. Oneida's correction table raises the horsepower needed by 1.16 times at 5,000 ft and 1.48 times at 9,000 ft, so a 2 HP shop at 9,000 ft needs about 3 HP.