By Martin Harris.

DIY and Small-Shop Dust Collection System Design

Planning a whole shop dust collection system is a different problem than picking a good collector. I get emails and forum questions from people who bought a genuinely capable unit, hooked it up, and were still disappointed with how their shop performed. Nine times out of ten, the collector was never the weak link. The duct layout, the branch sizing, or the blast gate setup was.

This guide walks through the whole planning problem in order: collector, then duct, then gates, then filtration. Skipping ahead to buy a bigger collector before fixing the duct layout is the single most common mistake I see in this hobby.

The whole-shop planning problem

A dust collection system is exactly that: a system. Every source I trust on this, Bill Pentz, Oneida, Spiral Manufacturing, all describe the same basic chain: capture dust at the source, transport it through duct, separate the bulk debris, filter what remains, and maintain the system so performance does not degrade over time. Any one stage in that chain can become the bottleneck, and a common mistake is throwing money at the collector when the real problem is duct sizing or a leaky fitting three stages downstream.

Before buying anything, walk your shop and sketch a rough floor plan. Mark where your stationary tools sit, where a collector could realistically go, and how duct would have to run to reach each machine. This sketch, even a rough one, will save you from discovering mid-installation that your planned duct route runs straight through a doorway or a support post.

System design principles

• Size for your highest demand tool, not your average one. A planer or wide belt sander can call for 400 to 500 CFM or more, while a router table might only need 300 to 400. If your collector is sized to the average of your tools rather than the highest single demand, the planer will always be the machine that underperforms.
• CFM and static pressure have to be considered together. A collector's rated CFM is measured under ideal conditions, not through your actual duct run. Every foot of duct, every elbow, every wye fitting, your cyclone if you run one, and your filter all add resistance, expressed as static pressure in inches of water column. A fan that looks great on paper can deliver much less once your real system is attached. This is the single most misunderstood concept in small shop dust collection, and it is worth spending real time on the static pressure and CFM math before buying anything.
• Rigid duct beats flex hose, every time distance is involved. Flexible hose is convenient right at the tool, where you need to connect and disconnect or reach an odd angle. It is also measurably worse than rigid pipe for preserving airflow. Keep flex sections short, generally a few feet at most, and run rigid duct for anything longer.
• Plan your main duct size around your collector's real output, not your tool's port size. A common mistake is sizing every branch to match a stationary tool's 4 inch factory port, even when the collector and main line could support 5 or 6 inches. Oneida's guidance is direct on this: tool port diameter is often a packaging decision, not the correct duct size for your system.

Step by step planning

1. List every tool that needs collection and its approximate CFM demand. Use published heuristics as a starting point: a table saw around 350 to 450 CFM, a planer 400 to 500, a jointer 350 to 450, a router table 300 to 400, a bandsaw 350 to 400. These ranges come from manufacturer and industry sources like WorkshopCalc and Oneida, and they are a starting point for planning, not a guarantee for your specific tool and hood setup.
2. Identify your highest single demand tool. That number, not an average, sets your minimum collector target once you account for duct losses.
3. Sketch your duct route. Aim for the shortest reasonable run from collector to each tool, minimize the number of elbows, and avoid tight 90 degree turns where a 45 degree or a wye fitting would work instead. Every elbow adds measurable static pressure loss, more at smaller diameters.
4. Size your main and branch duct. A common pattern from real shop layouts, described in Woodcraft's central system design guide, starts with a 6 inch main, steps down to 5 inch branches for larger machines, and 4 inch branches for smaller tools. Your specific numbers will depend on your collector and tool list, but the stepping-down pattern, rather than one uniform size everywhere, is a reasonable default.
5. Plan blast gate placement. Put a gate at every branch so you can close off tools you are not using and concentrate available airflow at the active machine. Running multiple gates open at once splits your CFM across all of them, starving every tool at once.
6. Plan your separator and filter stage. If you are running a cyclone or a baffle separator, budget for its pressure drop, roughly 2 in. w.c. as a starting figure, though actual separator drop varies by model and flow rate. Your filter's condition matters here too: a loaded filter adds resistance over time even if nothing else in the system changed.
7. Leave room to expand. If you plan to add tools later, oversize your main duct modestly now rather than tearing it out later. It is much easier to add a branch to an appropriately sized main than to replace an undersized one.

Example builds by shop size

One-car garage, 2 to 3 stationary tools.

A single mid sized collector, 4 to 5 inch main duct, short branch runs. Portability matters here since the shop likely serves double duty; a mobile base on the collector is worth the modest cost.

Two-car garage, 4 to 6 stationary tools.

This is where a genuine central system starts to pay off: a 5 or 6 inch main, stepped down branches, and a fixed collector location rather than dragging a portable unit around. A cyclone pre-separator becomes more worthwhile here since you are moving more total dust volume and want to protect filter life.

Dedicated small shop building, 6+ tools plus a planer or wide belt sander.

Plan around your highest demand tool from the start, likely a 5 to 6 inch main minimum, and take filtration seriously since you are running the system for longer stretches. This is also the point where a two-stage cyclone setup starts to make real sense over a single-stage collector, both for separation efficiency and for filter protection.

Recommended gear

Start with my CFM calculator to work through your specific numbers, then see my best dust collection system for small shops roundup for collector picks, my ductwork guide for duct sizing detail, and my best blast gates roundup for gate hardware.

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