What Is Flex Ductwork? A Comprehensive Guide

In the design of modern HVAC systems, ductwork is and has always been one of the most critical components. These are the passageways through which air passes, and as you can imagine, having the right ductwork helps you to significantly improve the overall quality of your heating and cooling system.

Today, the flex ductwork is easily one of the most popular ductwork types. Known for its unique shape and profile, a flex duct can significantly improve airflow and optimize the efficiency of your HVAC system. Let’s find out more about how this duct works and all you need to know about it.

What is Flex Ductwork?

Some call it a flexible ductwork, others call it a flex duct. However, the industry name remains “flex ductwork.”

This here is a type of ductwork that is usually applied in HVAC systems to help transport air from one point to the other. Flex ductworks come with flexible materials – usually metal or plastic – in their inner core, with this material itself being surrounded and covered by an outer layer of protective material.

As you can imagine, the flexibility of this ductwork is what makes it especially popular. You can easily route a flexible ductwork around obstacles, place it in a tight space, or even use it to form across an area with an irregular shape. Whether you’d like to bend or twist it, a flex ductwork is perfect for you. All in all, you get an easy, cost-effective installation method that won’t be much of a hassle.

Every flex ductwork you see has a typical basic structure that consists of three primary components.

The Inner Core:

Probably the most important part of the duct is the inner core, which is usually made of a flexible material. In most cases, you get polypropylene or polyethylene. Or, if you’d like something more metallic, an aluminum material is pretty solid for you.

With the inner core, you have a reliable pathway that allows air to flow from the HVAC to the part of the building you’d want. It’s flexible, so you can bend and shape the ductwork as you please.

An Additional Insulation Layer

It’s also important for you to surround the inner core with insulation material. This insulation makes it easier to regulate the temperature of the air you’re passing through, thus cutting down on heat loss or gain as the air moves through the duct. Foam, fiberglass, and other synthetic materials are usually applied as insulation.

The Outer Jacket:

Both the insulation and the inner core are encased within an outer jacket. The job of this layer is to ensure that the ductwork is durable and to protect it from external interference.

In most cases, your jacket is made of a foil, a plastic, or maybe even a combination of both materials. As long as it’s able to protect from environmental factors, it’s good to do. At the same time, it’s recommended that you get an outer jacket with a reflective material – this way, you bolster energy efficiency and prevent the risk of heat transfer.

How Does Flex Ductwork Work?

So at the moment, we all understand the importance of a flex ductwork – to ensure that heat is properly transferred, and that air is able to move from point to point in any building.

For a flexible ducting system to work well, a few things need to be in place. These include:

Proper Airflow: The entire process really starts with the HVAC system, which generates conditioned air – it could be heated, it could be cooled. From here, the air is pushed or pulled through the system’s primary ductwork.

The Flex Duct Connection: At several strategic points within the HVAC system, you connect the flex ducts to the min rigid ductwork. Connectors, collars, and other fittings are mostly used to make these connections.

Moving Through Spaces: As explained earlier, one of the benefits of HVAC flex ductworks is the fact that they are incredibly flexible. Thanks to this, you can easily route them through even the tightest of spaces – or around obstacles and parts of the buildings with irregular shapes.

Air Distribution: As soon as air is introduced into the duct, it travels through its channel to reach the designated room or area within the building. Once again, you have to rely a lot on the flexibility of the ductwork to adapt to the building’s contours and structure.

Additional Air Insulation: As the conditioned air moves through the duct, it passes through the insulation area that surrounds the duct’s inner core. Remember – this layer focuses on minimizing heat gain or loss, especially as the air moves from one point in the duct to the other.

Implementing Proper Ventilation: In areas where you need to deliver the air, you can attach diffusers or registers to all of the ends of the ductwork. This way, the vents are able to properly distribute the air into the space, making possible seamless ventilation.

Factors Influencing Airflow Performance

On its own, a flex ductwork can be effective when it comes to optimizing and regulating the flow of air as much as possible. However, this isn’t to say that you don’t need to be aware of some other factors that play a role in improving the efficiency of this process.

A few of these factors include the following:

The Size & Design Of The Duct:

First off, you need to make sure that the duct is appropriately sized and properly designed. Both factors play a huge role in the performance of the HVAC flex duct, as overly small facts can actually restrict the airflow. When a duct is sized right and transitions are properly designed, airflow can be optimized as much as possible.

The Duct Layout & Length

Next, we have the length and layout of the duct, which can impact airflow resistance. When ducts run longer and you have complex layouts with different twists, you run the risk of increasing static pressure and cutting down on airflow. Instead, you need to make sure the layout is optimal, with short and straight runs as well as just a few bends.

Material & Insulation Choices

Airflow performance also depends significantly on the material of the ductwork and the efficiency of your insulation. Combined, both will help to reduce air resistance as much as possible, while also promoting efficiency in overall airflow.

The Speed Of Air Itself

As air travels through the flex ductwork, it does so at a specific speed. This velocity will influence airflow performance, with high air velocity resulting in increased turbulence. At the same time, when air doesn’t move quickly enough, you might not be able to supply it to every part of the building.

The Presence Of Grilles & Registers

We mentioned earlier that flex ductworks typically come with grilles and registers. Well, the size and location of these components can also impact the distribution of airflow. When registers are sized and placed right, you can ensure that air will move seamlessly through the building, so there are no hot or cold spots.

How Clean Is The Air?

If you don’t have air filters or your air isn’t clean for some reason, you can imagine its impact on airflow and overall HVAC efficiency. This is why you need to ensure proper maintenance and cleaning of your air filters – and if the need arises, feel free to replace them!

Dampers & The Balancing Act

Having adjustable dampers within your ductwork will also make it possible for you to balance your airflow and ensure that conditioned air is properly distributed across different rooms or zones within the building. As such, they improve airflow performance optimization and help with energy efficiency.

External Environmental Factors To Consider

We should also remember the place of environmental factors like humidity, temperature, and altitude – as well as the effects that they can have on general airflow performance. In some cases, you might need to modify your HVAC systems to compensate for these factors generally.

Types of Flex Ductwork

Flex ductworks generally come in different types, all of which help to fulfil one particular objective or the other. With these ductworks, you generally get a lot of options to choose from when making a choice:

The Non-Insulated Ducts:

While insulation is seen as a critical part of the flexible ductwork, some of them don’t actually come with any. They are specifically used in situations where you don’t need any insulation, such as in ventilation exhaust systems or warmer climates.

Insulated Flex Ducts

The direct opposite of the first, these ones come with their inner cores being surrounded by proper insulation. As you can imagine, the goal of the insulation here is to cut down on heat transfer and make sure that temperatures within the ductwork are as consistent as possible.

Metalized Flexible Ducts:

These flexible air ducting tools come with a reflective outer jacket, which is usually made of some metallic material like aluminum. They work in situations where you need thermal insulation, just like the insulated ducts.

Low-Pressure Flexible Ducts:

The low-pressure ducts are built to be used in systems that have low air pressure – including and especially in residential HVAC systems. They are flexible and light, so installing them should be a breeze. However, in high-pressure situations, they tend not to be so great.

High-Pressure Flexible Ducts:

When you have those high-pressure needs, these are the ducts you choose. They work best in industrial and commercial settings, where you need more airflow. In fact, most of these ducts come with additional layer reinforcements that help to optimize durability as much as possible.

Fire-Rated Flexible Ducts:

The fire-rated ducts are built with materials that have been passed for fire safety and are built to prevent the spread of flames or fire. Considering that fire safety is an important fixture in most situations, you can imagine that these ducts are especially important.

Antimicrobial Flexible Ducts:

Besides the insulation that surrounds them, these flex ducts also come with treatments and coatings that prevent the growth of mildew, mold, bacteria, and other contaminants. This way, you don’t just ensure proper airflow – you also optimize its quality as much as possible.

Pros and Cons of Flex Ductwork

Considering the fact that they are not the only types of ductwork, you might be wondering what could set these ones apart from their main competitors. Well, with flex ductworks, you pretty much get the good with the not-so-good. So, here’s a breakdown of what their pros and cons are.

Where Flex Ductworks Shine

As you can imagine, the flexibility of a flex ductwork is its biggest draw. You can easily move it around tight spaces, obstacles, and more, making installation easier and more adaptable

Generally, a flexible air ventilation duct is also much more cost-effective to work with – both in terms of the cost of materials and the process of installation

Because they have fewer seams and joints compared to others, flex ductworks don’t have much of a risk of air leakage

At the same time, the flexibility and insulation available in a flex ductwork ensures that noise transmission from the HVAC system to the required spaces is as little as possible.

Comparatively, flex ductwork also does a much better job of accommodating to the setting and movement of buildings. This helps to prevent ductwork damage, while also maintaining the right airflow.

The Demerits Of Flex Ductwork

While flex ductworks can be pretty impressive, they tend to be prone to collapsing or kinking if you don’t install them well. And, this will lead to restrictions in the general airflow.

At the same time, flexible air ducting also tends to have a relatively shorter lifespan, while also bruins susceptible to damage from everything – pets, moisture, impact, etc.

You could always add insulation to reduce heat gain or loss with flex ductworks, but there’s always a risk of this insulation also degrading over time or losing its overall thermal performance.

And, when you install a flex ductwork in a humid environment, you need to be especially wary of condensation buildup. By extension, this leads to issues such as mildew, mold, and other air quality challenges

If you care about the aesthetics of your building, then you might not like the way flex ductwork looks. And if you choose to conceal it, then you might need to have additional finishing work on the building

Flex Ductwork: Installation and Maintenance Procedures

If you think that a flexible ductwork is worth the investment – and, to be fair, you actually should – then you can pretty much go ahead and have it installed. For this to work, you need to be aware of a few critical steps:

Start By Designing Your Layout

Of course, you won’t just place the ductwork in your building and lay back. Before the actual installation, you need to carefully plan the positioning and layout of the system. Here, you need to consider factors like the airflow requirements, the size of the duct, and any possible constraints from the building.

Get Your Tools Ready

Gather all of the necessary tools and materials you would need for the installation – the ducts themselves, the collars, supports, connectors, and many more. As you do this, also make sure that the materials are up to code.

Start With Preliminary Work

Now, you’re getting closer to the installation of the flexible air duct. Make sure you clear your work area and remove any obstacles, so the ventilation is as optimal as possible.

From there, cut the flex ducts to the required lengths with scissors or a knife. Remember not to compress or crush them while they’re being cut, then shape them based on your needs to fit the building’s ideal layout.

Make Duct Connections

Thanks to collars and connectors, you can pretty much attach the duts to each other at their ends. You need to make sure that the connection is solid and secure, so you don’t get any air leaks. If you need to, make use of straps and metal clamps to secure them.

At the same time, you can also install hangers or supports at regular intervals to support the duct’s weight and prevent it from sagging down the line. These supports need to be properly fastened too, so they can offer enough clearance around the ducts.

Keep An Eye On Insulation

If your flex ductwork is to be insulated, then you need to apply the insulation material to cut down on heat gain or loss as much as possible. Once again, proper securing is key here, as the insulation needs to cover the entire stretch of the ductwork. At the same time, tapes and adhesive materials should be used to seal seams.

Test Your Entire Setup

Once you’ve sealed the seams and all the joints, you can have a final thorough inspection of the ductwork to make sure that it’s aligned, and that things like sealing and support are properly done. Then, test the system to verify that airflow is optimal.

If you have any additional finishing touches, then add them too. Close or finish any exposed ductwork as you need, then install the needed grilles, registers, or diffusers at the tail end of the duct runs to keep proper control of airflow.

It also helps for you to keep proper records of everything you’ve done throughout the installation process. From technical details to setups and more, always have an eye for details.

Flex Ductwork vs Rigid Ductwork

So we know just about everything there is to know about flex ductwork. What about the other ductwork type?

In most cases, HVAC systems tend to come with a combination of both flex and rigid ductworks. In the rigid structure, you have a duct system which – as its name suggests – is not flexible. These ducts are usually made of materials like sheet metal, rigid PVC, fiberglass, and more.

With its solid construction, a rigid ductwork maintains its structural integrity and shape without bending. Its interior surface is also very strong, thus facilitating efficient airflow and cutting down on pressure drop as much as possible. At the same time, it’s durable, being able to withstand things like physical contact and even contact with fire.

That said, another major characteristic of the rigid ductwork is your ability to fabricate it into different sizes and shapes. So, regardless of your HVAC system design, there’s a chance that a rigid ductwork should be able to get the job done for you.

Major Comparison Metrics

Okay, so we know what a rigid ductwork is now and how it differs from the flexible one. But, what are the lines of distinction between the two of them?

Overall Performance

When it comes to general performance, both options are actually pretty even. As long as the installation is done right, you won’t have a problem overall.

Installation Flexibility

On this front, the flexible ductwork actually comes out on top. Because of its flexible material, you will be able to generally install it easily, and the ductwork itself should be able to conform to whatever shape or requirements you have.

Cost-Effectiveness

We pointed out earlier that flex ductwork is usually more cost-effective in the long run. The ease of installation and low maintenance requirements mean that you generally won’t need to spend so much to have one installed in your building and up and running.

Durability and Longevity

That said, the rigid ductwork actually tends to be more durable in the long run. Its material is properly rigged, and it is much stronger – as long as you install it right

Etc.

Conclusion

Flex ductworks are all the rage when it comes to HVAC systems. Their flexible builds, as well as their long-term affordability, makes them very reliable when it comes to moving air from one point in a building to another.

The professionals at Xuan-Yuan are available to help you get your hands on the best flex ductwork – or if you need any additional information. Reach out to us and let us know what you need.