PVC Duct Design for an Industrial Ultrasonic Humidifier

The humidifier may be working normally while the room still receives uneven mist. In many projects the real restriction is the duct: it is too long, has a low point, starts branching too early, or sends most of the airflow through the first few holes.

PVC is widely used for ultrasonic humidifier distribution because it is smooth, corrosion-resistant and easy to modify on site. The layout still needs to be treated as an air-and-condensate system, not simply as a pipe carrying fog.

Keep the first section straight

Provide a straight section after the humidifier outlet before the first distribution hole or branch. This allows the airflow and mist to settle into the duct. A practical starting point is at least 1 metre, provided the model and site layout allow it.

A bend immediately at the outlet increases turbulence and can throw droplets onto the duct wall. Where a bend is unavoidable, use a smooth elbow and leave service access at the humidifier connection.

Use a continuous slope back toward the humidifier

Some condensation inside the duct is normal, especially during start-up, in cool rooms or when output is high. A continuous fall of roughly 1–2% back toward the humidifier lets this water return naturally when the equipment is designed to accept returned condensate.

Avoid U-shaped runs and unsupported sagging. Even a shallow low point can collect water, reduce the open duct area and eventually cause dripping from outlet holes.

Choose the duct diameter around airflow, not only the outlet fitting

The machine outlet establishes the starting connection, but total duct diameter must also suit the fan and the required run. Reducing the pipe too aggressively increases resistance and may leave the far end with little flow.

Do not place the full weight of the duct on the humidifier outlet. Support the pipe independently and use a removable connection so the machine can be serviced.

Position outlet holes above the horizontal centreline

Outlet holes positioned slightly above the horizontal centreline help reduce direct drainage through the holes. The PM Series manual uses approximately 30° above horizontal as a practical reference for ducted installations.

Hole size and spacing depend on duct length, airflow and the number of zones. A common starting range is 15–20 mm, followed by balancing during commissioning. Do not drill the full pattern before confirming how the first section behaves.

Balance the holes from near to far

If every hole is the same size, the openings closest to the humidifier often discharge more air. For longer runs, installers may use smaller or fewer openings near the machine and gradually increase the open area farther away. The final pattern should be verified on site because fan performance and duct resistance vary.

Plan branches carefully

Branches should divide airflow deliberately. A short branch and a long branch connected to the same tee rarely receive equal flow without balancing. Keep branch lengths similar where possible, or add adjustable dampers designed for wet air service.

Do not create a branch with a lower section that cannot drain. Each run needs either a return slope or a separate condensate route.

Seal the end unless the design requires an outlet

An open end can consume most of the available airflow and leave the side holes weak. Seal the end for a perforated distribution run unless the design specifically uses the end as a main outlet.

Commission the duct before final handover

Run the system first at moderate output. Inspect every joint, bend and low point. Check that visible mist leaves the intended outlets and that condensate returns without collecting. After the room approaches target RH, inspect again because evaporation conditions change as humidity rises.