When it comes to heating, ventilation, and air conditioning (HVAC) systems, the distribution of conditioned air throughout a building relies heavily on ductwork. Ductwork serves as a conduit, ensuring optimal airflow and creating a comfortable indoor environment to work in. In the UK, the HSE states that  “every enclosed workplace should be ventilated by a sufficient quantity of fresh or purified air’”. With this in mind, it’s pretty important to have an understanding of the primary types of ductwork available, and which are suitable for your workplace. 

Are you investigating the types of air ducts, or want to know the types of ductwork that exist? In this article, we will delve into the different types of ductwork commonly used, their benefits, applications and some of the materials used in ducting types too.

Types of ductwork

Before you consider ductwork installation, you’ll need to decide what material you want to use, and then the type of ductwork required to build the structure. Below are the three main types to be aware of.

1. Flexible ductwork

Flexible ductwork is used in homes and businesses, due to its versatility and easy installation. It comprises a flexible tube made from durable materials like plastic or aluminium, allowing it to bend and fit into a variety of different spaces. It’s the latter reason that businesses may opt for flexible ductwork, as it can easily fit into compact spaces that rigid ductwork might not be able to.

You can get flexible ductwork fabricated in various lengths, shapes and sizes to connect to existing air vents and registers in a building. They’re also a fantastic choice for reducing noise transmission too, so businesses that need to keep noise to a minimum may opt for flexible ductwork.

The downside of this type is its easy accumulation of dust and debris, so it’s important to get your ductwork cleaned regularly if you opt for this type in particular. Plus, there have been cases where kinks and bends in flexible ductwork have caused insufficient airflow, so it’s imperative that you check your flexible ductwork solution is installed correctly (should you go for this type). Our guide on how to improve airflow in air ducts covers everything you need to know.

2. Rigid ductwork

The next classification is rigid ductwork, which encompasses a variety of sizes, materials, and shapes, including rectangular and cylindrical designs. Unlike flexible ducts, rigid ducts are not prone to airflow restrictions caused by kinks or bends, and they are not susceptible to tearing or puncturing. However, due to their inflexible nature, they are not easily adaptable to challenging spaces. 

Rigid ductwork consists primarily of three types: sheet metal ducts, fibreglass-lined ducts, and fiberboard ducts. Let’s dive into each of these rigid ductwork types in detail:

Sheet metal ducts

Sheet metal is the most commonly used material for air ducting, and it comes in various forms such as galvanised steel, mild steel, or aluminium. Depending on their purpose and fit, these materials can be shaped into different forms, including rectangular, oval, or round. When selecting a material, you may encounter the term “corrugated metal,” which refers to any type of sheet steel strengthened for construction purposes through a series of grooves and ridges. 

It’s important that your sheet metal ductwork adheres to DW144 specifications through the use of galvanised steel. But what is galvanised steel? It involves adding a layer of zinc to steel, which acts as a protective barrier, safeguarding the underlying steel against scratches and rust. Alternatively, a fully-welded high-integrity ductwork solution is best suited for addressing challenging issues related to dust, fumes, and odours in harsh industrial settings.

Fibreglass air ducts

Fibreglass air ducts are sheet metal ducts that have a fibreglass liner either inside or outside the duct. This liner insulates the duct, preventing air leaks and reducing condensation issues that typically come with fibreboard ducts

Fibreglass-lined ducts are excellent for sound insulation, reducing noise generated by HVAC systems. As a result, these ducts are commonly found in office and commercial buildings. However, it is important to note that fibreglass degrades over time, leading to the release of airborne particles that can pose potential health risks. This can undermine efforts to comply with EH40 exposure limits, so if health concerns are paramount, fibreglass ductwork may not be suitable. Additionally, cleaning fibreglass air ducts can be challenging as they are prone to mould growth if not properly maintained.

Fibreboard ducts

Fiberboard air ducts are a popular type of rigid ductwork used in HVAC systems. These ducts are crafted using a composite material that combines resin-bonded glass fibres, often with compressed wood fibres. This unique composition results in a lightweight, yet robust material for ductwork that has great insulation.

They typically come in rectangular shapes, and fiberboard ducts are renowned for their exceptional thermal and acoustic insulation. They find widespread application in residential and commercial buildings where noise reduction and energy efficiency are needed. Fiberboard air ducts are often fairly easy to install and are a cost-effective solution. However, proper sealing is crucial as they can be prone to moisture absorption and mould growth, which can cause a whole host of issues for workers and residents alike.

3. Semi-rigid ductwork

Semi-rigid ducting (also referred to as semi-flexible ducting) falls in between the rigid and flexible categories, striking a balance between their respective characteristics. It is typically crafted from a blend of aluminium and polyester materials to achieve a combination of flexibility and structural integrity.

A notable advantage of semi-rigid ducting is its capacity to maintain its shape once installed, eliminating the risk of drooping or bending that may occur with flexible ducts. This attribute promotes efficient airflow and reduces air resistance. It is commonly employed in straight or slightly curved configurations where a sturdier structure is required, while still allowing for some flexibility to manoeuvre around obstacles. Plus, semi-rigid ducting is offered in various sizes and lengths to accommodate diverse ventilation needs – it can be easily cut and adjusted on-site, making it suitable for both residential and commercial applications. 

Now you know what the main types of ductwork are, contact Airmatic to find the best ductwork solution for you. From bespoke fabrications to high-integrity ductwork, we can tailor a solution to suit your HVAC requirements.