Transport Velocity: The Starting Point
Wood dust and chips require a minimum air velocity to remain suspended in the duct rather than settling out. For fine wood dust, most industrial ventilation guides cite a minimum transport velocity of 3,500–4,000 feet per minute (fpm) in horizontal runs. Vertical or angled runs can tolerate slightly lower velocities since gravity assists transport downward, but horizontal segments are the critical constraint in most hobby shop layouts.
A correctly sized duct maintains adequate velocity throughout the run. Oversizing the main trunk reduces velocity below the transport minimum; undersizing raises velocity but increases system resistance and motor load. Both outcomes reduce collection efficiency.
Main Trunk Diameter
Most 1–1.5 HP single-stage collectors commonly found in Canadian hobby shops are designed around a 4-inch or 5-inch main port. A 4-inch trunk handles a single tool connection adequately. If two tools may run simultaneously or if the trunk feeds more than one branch, a 5-inch or 6-inch main line is typically needed to maintain velocity through the larger cross-sectional area.
For a layout with a main trunk and multiple branch drops, the trunk is sized for the total airflow, then steps down at each branch takeoff. Running a 6-inch trunk to a first branch at 4 inches, then continuing with a 5-inch trunk to a second branch, is a common stepped approach that maintains velocity throughout.
Branch Hose Diameters by Tool Type
Different tools produce different chip and dust volumes and require different port sizes. Most stationary power tools come with a 4-inch dust port as standard. Some smaller tools (routers in tables, scroll saws, spindle sanders) use 2.5-inch ports. A few larger tools (wide-belt sanders, drum sanders, large planers) benefit from 5-inch connections.
| Tool Type | Typical Port Size | Notes |
|---|---|---|
| Table saw | 4″ | Both blade guard and under-table ports benefit from separate connections |
| Jointer (6″–8″ models) | 4″ | High chip volume; benefits from direct duct connection rather than flex hose |
| Thickness planer (12″–15″) | 4″ | Very high chip volume; single-stage bag fills quickly |
| Bandsaw | 4″ (lower) / 2.5″ (upper) | Lower port handles most chips; upper port adds fine dust capture |
| Router table | 2.5″–4″ | Fine dust; MERV 13+ filter recommended |
| Random orbit / belt sander | 1.25″–2.5″ | Very fine dust; consider separate shop vacuum with fine-dust filter |
Flexible Hose vs. Rigid Ducting
Corrugated flexible hose is easier to route around obstacles and to connect to tool ports with standard fittings, but it introduces more resistance than smooth-wall rigid duct. In practice, hobby shops often use rigid sheet metal or PVC pipe for wall-mounted trunk lines and flexible hose for the final 1–2 feet at each tool connection.
When using flexible hose, stretched taut produces less resistance than the same hose left slack with folds. A hose that collapses inward at any point (often visible as flattening under suction) indicates either a material issue or that the hose is undersized for the vacuum pressure from the collector.
Blast Gates and Multi-Tool Layouts
In layouts serving more than one tool, blast gates (sliding or rotating shutoffs at each branch) allow closing unused ports to direct the full airflow to the active tool. Without blast gates, a system designed for one 4-inch connection will have its velocity distributed across all open ports, often dropping below the transport minimum at each.
Blast gates should be installed close to the tool connection rather than at the main trunk, so that the branch hose leading to the gate is also cleared by the airflow when the gate is open.
Seasonal Considerations in Canadian Shops
Detached garages and workshops in Canada face significant temperature swings. PVC ducting can become brittle at temperatures well below freezing and may crack if struck or if the system is run without adequate warm-up. Metal ducting handles cold temperatures without material degradation. In an unheated shop, allowing the collector to run briefly to equalize temperature before full operation can reduce thermal stress on plastic components.
Condensation inside ductwork can occur when a cold shop warms up rapidly, particularly with propane or wood stove heat. Moisture in the duct traps fine dust on the walls and can reduce effective diameter over time. Regular inspection of horizontal runs is useful in shops with high humidity swings.