A duct run can look straightforward on a drawing, then become the source of noise, grease leakage, poor capture or difficult installation once it reaches site. The difference is usually in the specification, not simply the diameter of the duct. This DW144 ductwork specification guide explains what commercial kitchen and industrial buyers should confirm before ordering ductwork, fittings and fabrication.
DW144 is the recognised UK specification for sheet metal ductwork construction. It gives a common framework for how ductwork should be made, joined, stiffened and tested where required. For contractors, facilities managers and kitchen operators, it provides a useful way to make sure every party is working to the same construction standard rather than relying on a vague request for “commercial-grade ducting”.
What DW144 Covers in Ductwork Specification
A DW144 specification is concerned with the physical construction of sheet metal ductwork. That includes the material thickness appropriate to the duct size and duty, joint types, flange construction, reinforcement, sealing arrangements, support requirements and permissible air leakage.
It applies to rectangular ductwork and is often used alongside circular spiral ducting and fabricated fittings within the same system. A complete job may include straight duct sections, elbows, branches, reducers, spigots, access doors, silencers, weather terminals and fan connections. Each item needs to suit the system pressure, air type and installation environment.
The standard is not a full ventilation design manual. It does not decide the airflow required over a cooking appliance, determine the fan duty, or replace a fire strategy. In commercial kitchens, DW172 is also highly relevant because it addresses kitchen ventilation design, canopy capture, grease extract arrangements and cleaning access. Think of DW172 as setting key requirements for the kitchen extract system, while DW144 defines how the sheet metal ductwork is constructed.
Start With the Air You Are Moving
The right specification depends first on what passes through the duct. Supply air, general extract, workshop fume extract and kitchen grease extract place different demands on the material, joints and maintenance provision.
For a commercial kitchen, grease-laden extract needs particular care. Joints must be properly sealed, changes of direction should be planned sensibly, and access for cleaning cannot be treated as an afterthought. A long run with inaccessible bends may be difficult and costly to maintain, even if it initially fits the available route. A well-laid-out system makes cleaning access practical from the beginning.
Industrial applications also need a clear description of the extracted air. Heat, moisture, dust, oil mist and process contaminants may affect the material choice and fan selection. Standard galvanised ductwork is suitable for many general ventilation duties, but it is not automatically the right answer for every environment. Where corrosion resistance, wash-down conditions or a particular process demand it, stainless steel can be specified.
Material Grade and Thickness Are Separate Decisions
Buyers sometimes ask for “stainless ductwork” without confirming the grade, thickness or duty. Those details matter. Stainless steel is not one universal product, and heavier material is not automatically necessary if the duct size, pressure and environment do not call for it.
For fabricated stainless components, 430 grade is a practical standard option for many commercial applications. Where improved corrosion resistance is required, 304 grade may be the better choice, particularly where the environment or cleaning regime is more demanding. It carries a higher material cost, so it should be selected for a reason rather than assumed on every project.
Thickness is similarly linked to the duct dimensions, pressure class and required stiffness. Larger rectangular ducts generally require more attention to panel rigidity and reinforcement than small sections. Specifying a thin sheet without considering the finished duct construction can lead to drumming, movement and joint stress. Conversely, over-specifying thickness across a simple low-pressure run can add unnecessary cost and weight.
A useful enquiry states the duct dimensions, material grade, finish, intended air use and whether the item is standard or made to measure. This allows the manufacturer to quote the construction required rather than making assumptions that may not suit the installation.
Pressure and Leakage Class Need to Be Clear
Not every ventilation system needs the same leakage performance. DW144 uses air leakage classes to define acceptable leakage from ductwork at a stated test pressure. The suitable class depends on the system type, operating pressure, energy expectations and project requirements.
Higher leakage control can be valuable where fan energy, air balance or containment are critical. However, specifying a tighter leakage class can involve more detailed sealing, testing and site coordination. It is sensible where the design calls for it, but it should not be added as a generic phrase without confirming how compliance will be checked.
Pressure classification matters too. Ductwork exposed to higher positive or negative pressures may need stronger joints, heavier construction or additional stiffening. This is especially relevant in longer industrial extract runs, systems with significant resistance, or installations where a fan is positioned so that part of the duct is under greater negative pressure.
The practical point is simple: give the duct fabricator the design pressure and leakage requirement, not only an airflow figure. Airflow helps size the system, but it does not fully define the construction standard.
Joints, Fittings and Supports Affect the Finished System
Most duct problems occur at connections rather than along a straight section. Poorly selected or poorly sealed joints can allow air, odour or grease to escape. They can also make a system harder to dismantle, inspect or modify later.
For rectangular ductwork, the joint and flange arrangement must be appropriate to the duct size and pressure duty. For spiral ducting, fittings should match the nominal diameter and connection method, with joints sealed and mechanically secured as required by the design. Do not assume that two components with a similar stated size will make a satisfactory connection without checking the spigot or socket arrangement.
Elbows, tees and reducers also deserve attention. A tight bend might save space, but it can raise resistance and noise. An abrupt reducer may be cheaper to fabricate than a gradual transition, yet it can affect airflow distribution. There is no single fitting layout that suits every job - the available space, fan duty and need for service access all matter.
Supports should be treated as part of the ductwork package, even if they are installed by another trade. The route needs suitable hanger locations, consideration for duct weight and clearance for access doors, insulation or fire protection where these are part of the project. A duct section that is well made in the workshop can still be compromised by inadequate site support.
What to Put on Your Ductwork Enquiry
A clear specification reduces back-and-forth and makes quotations easier to compare. For a meaningful DW144 ductwork enquiry, provide the following details:
- duct shape and internal or external dimensions, plus the route or drawing where available
- application, such as kitchen grease extract, fresh-air supply or industrial process extract
- design airflow, pressure information and any stated leakage class
- material requirement, including galvanised steel or the required stainless steel grade
- insulation, access door, weatherproofing and finish requirements where applicable
- fittings required, including elbows, branches, reducers, silencers, caps and fan connections
Kitchen Extract Requires Joined-Up Specification
A kitchen canopy, fan and duct run must work as one system. A correctly sized canopy cannot compensate for an undersized duct route, and a powerful fan cannot solve a poor capture arrangement or badly planned grease extract path. The ductwork should be considered alongside canopy dimensions, cooking equipment layout, fan location and discharge position.
Cleaning is central to this. Access panels should be positioned where they can genuinely be reached, especially after direction changes and along longer runs. A panel hidden above a fixed ceiling or behind services is not useful in practice. The installer, kitchen operator and fabricator should agree the access strategy before fabrication begins.
CanopyMan manufactures ducting, duct fittings and bespoke stainless fabrications from Birmingham for projects across England and Wales. For made-to-measure work, providing a sketch, site dimensions and the intended duty at enquiry stage helps ensure that duct sections and fittings are built for the actual route rather than an estimate.
Avoid Treating DW144 as a Tick-Box Exercise
Requesting DW144 construction is a sound starting point, but it is not a substitute for a complete specification. The best result comes from matching the duct construction to the system duty, choosing materials honestly, allowing for maintenance and confirming the interface between every component.
Before placing an order, take one final look at the route from canopy or collection point to discharge. Check each change in direction, every support position and every cleaning access point. Those practical details are what turn a drawing into ductwork that can be installed, operated and maintained properly.