Define the boundary first
A pressure-drop figure is useful only when you know what it includes and the airflow at which it applies. A cupboard figure may cover the enclosure alone. It may exclude connecting ductwork, fittings, silencers and the discharge arrangement.
Ask for every quoted figure to identify its boundary and units. Keep the cupboard manufacturer’s data alongside the system designer’s calculations so components are neither omitted nor counted twice.
Build a resistance schedule
| Item | Information needed |
|---|---|
| Cupboard | Model, operating airflow and quoted pressure loss. |
| Straight duct | Material, diameter, length and route. |
| Fittings | Bends, branches, transitions and connection geometry. |
| Other components | Silencers and any specified treatment equipment. |
| Discharge | Outlet arrangement and relevant boundary conditions. |
Our ducting guide and silencer guide help identify component questions for that schedule.
Use the duty point to discuss the fan
The required airflow and pressure belong together. A fan’s free-air figure describes a different condition from operation through a complete duct route. Compare proposed equipment at the project’s required duty and check the basis of the manufacturer’s performance curve.
Use our exhaust fan selection guide to prepare the equipment enquiry. Changes near a fan inlet or outlet can also affect installed performance, so show those connections on the drawing.
Our fan-curve reading guide shows how to follow the axes and duty point. Keep airflow units and conversions consistent across the equipment schedule.
Review changes before installation
An extra bend, a longer route or an added component changes the design information. Record the change and ask the responsible designer to review its effect before the installation is closed up.
- Keep the approved route revision with the equipment schedule.
- Confirm the selected fan and its control arrangement.
- Identify access for inspection and testing.
- Retain the commissioning results with the final drawings.
This gives the facilities team a useful baseline when later modifications are proposed.
When reviewing test information, distinguish duct velocity from volume flow. For a new route, use the duct-sizing brief to record dimensions and connections.