When specifying vents and ducts for a ductwork system, the two primary considerations for designers are capacity and efficiency.

Designing ductwork often leads to a variety of innovative solutions to solve problems, usually brought about by site space limitations.

In this article, we’ll cover some of the most important considerations when specifying vents and ducts to help your project go smoothly.


Ductwork and vents are commonly made from rubber, stainless steel, polyurethane, silicone, UPVC and GRP (glass-reinforced plastic).

The best material for the job depends on the following factors:

  • Flow rate requirements
  • Size and space available
  • The gases and air being transported
  • The environment in which the ducts and vents will live

Plastic ducting made from UPVC, as well as GRP-reinforced or lined plastic ducting for external applications, has become the standard choice in applications where corrosion is an issue such as with fume venting and chemical gas extraction.

You can find out more about the different types of ductwork here.


Location is an essential duct system design consideration because location

can affect cooling, accessibility and system performance.

The layout and characteristics of the structure’s floor plan are also critical considerations because they determine the types and specification of ducting that can be installed. Space is a significant limiting factor you need to keep in mind.


What processes will your vents and ducts be involved in? If you want to transport gases from one process to another, for example for odour control, you may need insulated ducts or reinforced ducts if you will be working with high pressures.

PVC GRP Ducting


When we design ductwork and vents, the intended use case is at the centre of our decisions. Vents and ducts should be specified with the process in mind to ensure that they meet performance, efficiency and safety requirements.



The primary aim when designing ductwork is to ensure that the design can deliver the intended flow rate for the process. This means delivering the proper amount of air (cfm), at the specified velocity (ft/min).

Several factors influence overall duct capacity, including:

  • Duct diameter
  • Duct shape
  • Ductwork size
  • Ductwork design
  • Fan specification
  • Vent specification


Whether ducting intends to transport gases from one process to another, is part of an air cooling system, or is part of a fume scrubbing system, efficiency is calculated into the design to ensure desired flow rates and efficiencies are achieved.

There are two key areas involved in ductwork efficiency:

  • Maximising flow rates
  • Minimising energy losses

When efficiency is built into the design of ducting, the following factors are considered: sealing, overall capacity of the duct, linings, duct diameter, duct shape, thermal expansion, condensation build up, extraction and future maintenance.

Talk to us about your project

PDFL specialises in the design, supply, assembly and installation of ducts, vents, liners, and stacks at plants and in industry. We offer industry-leading solutions and can design and fabricate ductwork to any specification.

For a chat about your vent and ductwork needs, call us today on +44 (0)1922 418005 and one of our specialists will make time for you.