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What are the Different Kinds of Air Ducts in HVAC?

There are four common types of ducts

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Air Ducts



In every HVAC system, one of the most important elements to check is the Duct (air ducts) system or what is known as ductwork. Ducts are passages that are used in heating, ventilation, and air conditioning to provide and remove air. They are used in different HVAC elements like air supply, air processing units, air return, diffusers, and more.

To be able to achieve a high efficiency HVAC system, the type of ductwork should be adequate enough and sized correctly for the system.

The types of ducts that are installed depends on the quality of the installation since their benefits vary from energy savings to the acoustic properties of the system.

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There are four common types of air ducts that are being used by HVAC engineers: Flexible ducts, Metal ducts, Glass wool duct boards and Plastic ducts.

1. Flexible ducts

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Flexible ducts are made up of two aluminum and polyester concentric tubes, wherein a glass wool layer or fiberglass wool is inserted in between the two tubes to serve as thermal insulation.

Their main use is to connect main air ducts and terminal units such as diffusers or grids.

Most flexible duct manufacturers are producing triple lamination of aluminum foil, polyester as well as metalized polyester film permanently bonded to a coated spring steel wire helix. The external part of the duct is wrapped with a blanket of fiberglass insulation.

2. Metal ducts


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Metal ducts are made from different kinds of sheet metal, like galvanized or stainless steel, copper and aluminum.

They are cut, and shaped into the required measured shape for the duct system. Being a good thermal conductor, metal ducts require thermal insulation as well.

The most common material used is fiberglass wool that is wrapped around the outer duct wall. Insulation can be installed on the inner wall of the duct as well using fiberglass wool duct wraps or duct slabs that are faced with glass matting or mesh. These provide acoustic insulation and strengthening the inner part of the duct.

3. Fiberglass Duct boards


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Fiberglass Duct boards are made from high density fiberglass boards.

The ducts will be shaped from the boards by cutting and folding respectively to get the needed shape for the system. The side of the board that has contact with the air stream after the duct assembly is called the internal face, while the other face is called the external face.

The external face of the duct will be installed with a strong reinforced aluminum foil that will act as a vapour barrier. On the other hand, the internal face will have either an aluminum coating or fabric layer depending on the requirements needed.

4. Plastic Ducts

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Plastic ducts which include ducts that are made from plastic or foam boards, are made by cutting and folding the needed shapes to create the cross-sectional shape of the duct system.

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The internal and external board faces are usually installed with aluminum coating.

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Engr. Amal Grover
A chemical engineer at Tata Chemicals. Indiana Institute of Technology alumni. Blogging about cool stuff. Follow me on Facebook


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