What's inside
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Start With the Machines, Not the Motor
Sizing a dust collector starts with the woodworking machines you need to connect, not with a horsepower number on a sales label. A 1-hp collector can work well on a table saw with a short hose, while a poorly ducted 2-hp unit may perform badly at the same tool.
Make a list of every machine and record its required airflow if the manufacturer provides it. Typical requirements are approximately 150 to 350 CFM for a table saw, 250 to 450 CFM for a 12- to 15-inch planer, 300 to 500 CFM for a jointer, and 350 to 600 CFM for a wide drum or thickness sander. A router table may need 150 to 250 CFM, depending on the enclosure.
These figures are working ranges, not guarantees. A machine with an open-bottom cabinet may need less airflow at the blade, but it can also leak chips into the room. A planer produces a large volume of chips and needs enough airflow to keep the discharge chute clear, even though its dust port may look small.
Decide Whether Machines Run Simultaneously
Most small shops use one machine at a time. If that describes your work, size the system for the largest requirement plus the losses in the ductwork. There is no benefit in adding the airflow requirements of every tool unless you genuinely expect to use them together.
For example, a 350-CFM table saw and a 450-CFM planer do not require an 800-CFM collector when only one is operating. A collector delivering roughly 600 to 700 CFM at the tool may be suitable, provided the duct system is short, smooth, and correctly sized.
If you want two machines operating together, add their required airflow and allow for pressure loss. A table saw and planer might require 800 CFM at the tools, but a practical design target could be 1,000 to 1,200 CFM at the collector. This usually means a larger impeller, 6-inch ducting, and a motor in the 2- to 3-hp class.
Understand CFM and Static Pressure
CFM is volume of air. Static pressure is the resistance the collector must overcome. A collector advertised as “1,200 CFM” may produce that number with no hose, no filter, and no duct attached. That is not the airflow your table saw receives.
Look for a fan curve showing airflow at a stated static pressure, ideally around 6 to 10 inches of water gauge for a small central system. If a manufacturer only lists free-air CFM, treat the number as a rough marketing comparison.
Every elbow, reducer, blast gate, flexible hose, separator, and filter adds resistance. A long run of 4-inch flex hose is particularly costly because its corrugated interior creates turbulence. A system that moves 900 CFM at the collector may deliver only 400 CFM through a restrictive 4-inch branch.
| Shop setup | Typical useful airflow at the tool | Practical motor range | Suitable use |
|---|---|---|---|
| Short hose, one machine | 300–500 CFM | 1–2 hp | Table saw, router table, small jointer |
| Fixed ducting, one machine | 500–800 CFM | 2 hp | Planer, jointer, table saw with better pickup |
| Several branches, one machine at a time | 700–1,000 CFM | 2–3 hp | Small central dust collection system |
| Two machines at once | 1,000–1,500+ CFM | 3–5 hp | Larger shop with 6-inch or larger ducting |
Match the Motor to the Duct Size
Use 4-inch hose for a single portable machine or a short connection. It is commonly adequate for a benchtop planer, router table, or compact table saw when the run is short. It becomes a restriction when stretched across a shop or used with a high-airflow collector.
Use 5-inch or 6-inch duct for larger machines and fixed runs. A 6-inch main duct can carry substantially more air with lower resistance than 4-inch hose. However, installing large duct on a weak collector does not create more airflow. The fan must have enough pressure capability to move air through the larger network and its filter.
For a typical one-person shop, a 2-hp collector with a 6-inch main and 4- or 5-inch machine branches is often a sensible middle ground. If the machines are spread across a large room, the duct run is long, or a cyclone and fine filter are included, a 3-hp unit gives more useful reserve.
Account for Cyclones, Filters, and Separators
A cyclone separator protects the filter and makes emptying the bin easier, but it also adds pressure loss. A fine cartridge filter improves indoor air quality, yet it can restrict airflow as it loads with dust. These components are worth using; they simply need to be included in the sizing decision.
For a small portable setup, a 2-hp dust collector with a cartridge filter can be a cheaper and perfectly adequate choice when you connect one tool at a time. For a permanent system, consider a cyclone separator system and allow extra capacity for its resistance.
Do not judge performance by the cleanliness of the floor alone. Fine particles that escape the machine or pass through a poor filter remain a breathing hazard. A ceiling air cleaner helps with airborne dust, but it does not replace source collection at the tool.
Avoid Common Sizing Mistakes
The most common failure is buying a high-horsepower collector and connecting it with undersized hose. The motor may draw plenty of power while the tool receives inadequate airflow. Another failure is running several blast gates partly closed; this creates additional resistance and often leaves chips in the duct.
Keep unused blast gates fully closed and seal leaks around machine ports, cabinet doors, and duct joints. Use smooth-walled duct where practical, ground metal ducting if required by your local safety rules, and keep flex hose only at the final connection. A clogged filter, overfilled collection bag, or packed planer port can reduce airflow dramatically.
A Practical Buying Target
For a small workshop with a table saw, planer, jointer, router table, and one operator, target at least 500 to 700 CFM at the active machine and choose a collector rated to deliver that airflow under resistance. A 2-hp unit is often the economical answer, especially with short duct runs.
Choose 3 hp when you need long duct runs, a cyclone, a large planer, frequent sanding, or more than one open blast gate. Choose a larger system only when the ductwork, electrical supply, and machine usage justify it. A bigger motor cannot compensate for a blocked filter, leaky duct, or undersized hose.