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Flexible Duct Connector: Everything You Need To Know

flexible duct connector

Are you wondering what a flexible duct connector is? Here is every question you may ask about that.

What Is a Flexible Duct Connector?

Flexible Duct Connectors are an effective way to reduce or even eliminate HVAC duct system noises and vibrations for both industrial and commercial applications. Using a flexible duct connector consisting of a fabric material that is securely fastened to steel metal on both sides, you will be able to isolate the vibration and noise from its source effectively.

In short, a Flexible Duct Connector is a flexible joint consisting of a fabric and two sheet metals securely fastened at both ends, used as a connector between equipment and ducting to isolate vibration and noise in the duct system.

image 1
A fabric is securely fastened by two metal sheets 

The name may sound similar to other terms, namely duct connectors and flexible ductwork. Among them, Flex ductwork is a type of long ductwork tube that is more flexible than rigid ductwork, making it ideal for spaces that are difficult to access. Many HVAC contractors will use rigid and flex ductwork to create a duct network that fits the space available in a home. On the other hand, HVAC duct connectors attach ductwork to equipment. They are made of fabric and can be attached to the sheet metal on both sides of the duct. Flexible duct connectors are designed to reduce or eliminate noise and vibration from fans or blowers in the duct system.

But there is another term that bears a close resemblance to flexible duct connectors:  flex connectors. But it is basically the same thing. Again, Flexible connectors are an essential part of many piping systems. They provide the flexibility needed to absorb vibration and noise, compensate for thermal growth, or permit the motion of other piping elements. Without flexible connectors, many piping systems would be unable to function correctly.

Why Use Flexible Connector?

The answer is in the definition. But again, the short answer is that flexible duct connectors are a necessary attachment between equipment and ductwork because they help to reduce vibrations and noises throughout the duct system. Unlike hard ductwork, flexible duct connectors also allow for a slight offset between the equipment and ductwork, which is essential for many reasons. By having this offset, it helps to reduce noise levels even further and also allows for different types of equipment to be used without having to replace the entire duct system.

The longer answer would be that all air duct installations for heating, cooling, or ventilation purposes have a fan or blower installed in the machinery. The vibrations, noises, and rattles from the fan or blower are turned on, carried through the metal ducts, and can be heard throughout the entire system. To reduce vibration and noise from the source, an air-tight flexible joint, a fabric sandwiched between two pieces of sheet metal, must be inserted between the equipment and the ductwork. This is called a “Flexible Duct Connector.” To meet every type of installation requirement, whether it is for a factory, institution, office, or home, manufacturers provide a large variety of flexible duct connector fabrics that can be assembled with ease.

Applications Of Flexible Duct Connectors:

Flexible duct connectors have a lot of applications in all sorts of fields; residential, commercial, semi-commercial, and industrial. On the whole, it is used to:

  • Isolating the transference of noise
  • Secluding and preventing the vibration transfer
  • Making up for any misalignment found in the network
  • Reducing the stress on the pipe network
  • The compressor connection with the discharge
  • Engine intake, along with exhaust piping
  • Pumps suction & discharge piping
  • Connections of Chiller inlets and outlets
  • FCU connection with ductwork and pipework
  • AHU connection with ductwork and pipework
  • Fans connection with ductwork and pipework

Types Of Flexible Duct Connectors:

Although you can find flexible connectors of many shapes, sizes, and types, they are usually categorized into 3 broad categories.

  • flexible duct connectors with flanges (which are often used for joining industrial duct fans)
  • flexible duct connectors with EPDM seals and male ends
  • rectangular duct connectors

But when you genuinely count all the types of flexible duct connectors, there are way more than these three categories.

Code Type Description
ILPRL Round to rectangular pressed take-offs with gasket ILPRL branches are supposed to connect spiral and square ducts to create a more efficient, highly ventilated system.
ILPR Round to rectangular pressed take-offs ILPR branches are ideal for fabricating ventilation ductwork joints at heat recuperation units in single- and multi-family houses.
ILPL Flat-pressed straight take-off with gasket. Flat straight branches are designed to connect round ducts, SPIRAL or plain, to the main square ducts. They are also used for the fabrication of expansion boxes in components like air supply diffusers, wall-mounted diffusers, ceiling air diffusers, etc.
ILP Flat-pressed straight branch without the gasket. Flat-pressed galvanized straight sheet branches without gaskets are typically used for the fabrication of expansion boxes in air supply diffusers along with ceiling and wall-mounted air diffusers.
ILSL Round to rectangular take-offs with radius with gasket Flat-branch ducts connect round SPIRAL or plain ducts to the main square ducts.
ILS Round to rectangular take-offs with a radius ILS flat segmented galvanized sheet straight branches without gaskets are used in the fabrication of plenum boxes, wall-mounted, and ceiling air diffusers.
ILSV-45 / ILSVL-45 Take-offs angle 45° ILSV and ILSVL take-offs are male-ended fittings, which can be used to connect round ducts and square ducts.
ASV-45/ASVL-45 Angle take-offs with mesh ASV-45 ASV / ASVL take-offs are male-ended fittings for use in round SPIRAL or plain ducts.
ILSN/ILSNL Take-offs with mesh – with or without gasket When you need to make a connection between pipes, the ILSN / ILSNL fittings are male-ended fittings that can be inserted directly into round SPIRAL or plain ducts.
ILA Flexible duct connector for circular ducts without flanges ILA male-end flexible duct connectors are used for joining two round SPIRAL or plain ducts. They are most often used for connecting air handling units and duct fans.
ILA-NSL Flexible duct connector for circular ducts with male ends and seals This flexible anti-vibration duct connector joins two spiral or plain round ducts. It has male ends and comes with a seal.
ILA-TK Circular, straight sleeve with clamps The ILA-TK is a flexible duct connector that helps to reduce vibrations in ventilation ducts caused by air handling units, fans, and other HVAC equipment.
ILA-FLS Flexible duct connector for circular ducts with flanges ILAs with flanges made from Flexible Liner Solder (FLS) are flexible duct connectors based on the original ILAs provided with additional FLS flanges to improve their stiffness. They are often used for connecting air handling units, heat recuperation units, and duct fans.
GALA Collar GALA GALA collars make segmented fittings, including bends, T-pieces, reducers, and dampers on a Gorelocker machine.
KILL Spigot plates with gasket The KILL square spigot plates are installed in square duct walls.
KIL Spigot plates -square KIL square spigot plates are designed to fit into square duct walls.

Types Of Coating Materials Used In Making Flexible Duct Connectors:

Here are the 4 commonly used coating materials from which flexible duct connectors are made.


Polyester fabric is very delicate in construction compared to other materials, suitable for general applications, and is a more economical choice. Usually in two colors, grey and black, the temperature ranges from -30℃ to +80℃.


Vinyl is the most commonly used material for duct applications due to its high tear strength, along with its high abrasion resistance. It is recommended for low to medium-pressure ductwork systems for the best results.


Silicone fabric is coated with unique silicon rubber that has excellent resistance to extreme temperatures, from the coldest to the warmest. It is recommended for indoor and outdoor installations for applications where high temperatures are of prime concern instead of ambient temperatures. The temperature ranges from -50℃ to +280℃.


The material canvas is typically used in applications that require high mechanical strength, including such diverse sectors as various industries, engineering, and architecture. It is resistant to humidity and mildew.

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Flexible Duct Connector Properties

A History Lesson: Flexible Duct Connectors Made of Asbestos:

Ducts that circulate air for heating and cooling are usually connected to HVAC machinery by connectors made of durable fabric. Textiles woven from asbestos fibers were the primary material for these applications for many decades until they were banned in the 1900s.

Metal air ducts connect all the rooms in a home or building to heating, ventilation, and air conditioning (HVAC) equipment. The problem is when ducts are attached to heaters and air handlers directly, the noise and vibrations produced by the equipment may rattle through the entire ventilation system. But the solution to this problem was very easy; install a flexible duct connector between the ductwork and machinery. This way, instead of vibration rattling the entire system, it would just be absorbed by these aforementioned connectors, which was convenient.

What was not so convenient was that when asbestos was widely used in the United States, flexible duct connectors commonly contained significant amounts of chrysotile asbestos. Factory workers who produced these connectors suffered the worst exposure to asbestos, followed by construction tradesmen who installed, repaired, or removed these connectors on a regular basis.

For many years, manufacturers made heat-resistant flexible duct connectors out of asbestos. Asbestos fibers are durable and fireproof yet flexible enough to be woven into fabric. During the 1980s, manufacturers began using other heat-resistant materials to make duct connectors. Yet even after being banned for so long, many international companies still use it in their machines, and many other countries have no policies to ban such items from entering their territories.

SuperAir Grey Silicone Flexible Duct Connector
SuperAir Grey Silicone Flexible Duct Connector


Will The Flexible Duct Connector Impact The Airflow Through The Duct System?

A flexible duct connector installed properly will not disrupt the airflow through the duct system. The size and installation of the flexible duct connector are essential and need to be done according to how long the fabric will span. If the fabric is allowed to fold or sag to significant amounts, it can reduce the airflow through the connector.

How Do I Choose The Right Flexible Duct Connector?

There are some key factors you should consider when determining which flexible duct connector is the most suitable for your needs. For instance, what is the maximum pressure the duct system can take? Or at what pressure exactly would it be running? Will the equipment be installed in the building’s interior or exterior? Then there are a few essential factors to consider when it comes to ductwork and the temperatures it will be exposed to. For example, what are the typical minimum and maximum temperature ranges for the ductwork? Will the flexible duct connector be exposed to any additional substances in the airstream? And finally, how large of a distance does the ductwork need to span?


SuperAir Black PVC flexible duct connector
SuperAir Black PVC flexible duct connector

Frequently Asked Questions:

What is the difference between a flexible air connector and a flexible air duct?

The length of a flexible air connector is just limited to 14 feet at max. At the same time, the length of a flexible air duct isn’t limited in any way compared to the first term.

Should you replace the metal duct with a flexible duct?

The metal duct is still used in older homes, but flexible duct is more prevalent in newer, modern homes. Both are effective; however, if you switch from metal to flexible ducts, don’t waste money on an HVAC contractor. It’s a time-consuming job, but it is something that you can do yourself.

How often should the flex duct be supported?

For a flex duct, the supports need to be installed at least every 4 feet to provide the best support. Additionally, the maximum sag allowed in the flexible duct is around one-half inch per foot. So, it would help if you placed supports at each of the connections between the flex and rigid metal ducts.

What is the disadvantage of a flex duct?

Like everything else, this ductwork also has some cons of its own. Namely, the decreased efficiency, which leads to higher energy bills. Another issue that is faced with this type of ductwork is durability because it is, well, flexible ductwork. The thing is, this one does not last as long as metal ductwork. On top of that, it is thin, which means that it can puncture with relative ease. Moreover, it does not have the durability of metal ductwork to withstand normal wear and tear.

What is a duct connector?

HVAC duct connectors are used to connect equipment and ductwork. They are made of fabric and are attached to the sheet metal of the duct on both sides. Flexible duct connectors eliminate noises and vibrations made by fans or blowers.

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