Types of Air Ducts

Air ducts are used to distribute air throughout a building or to exhaust air outside of a building. The duct is the channel that carries cooled air from the air conditioning unit through your home, and also removes warm or stale air. They are used in different HVAC elements like air supply, air processing units, air returns, diffusers, and more. In every HVAC system, one of the most important elements to check is the Duct system or what is known as ductwork. The most common are sheet metal, fiberglass lined, fiberboard, and flexible air ducts.


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. They are inexpensive, lightweight, and easy to install. It is important that the lengths of the flexible air ducts be kept as short as possible as the amount that they bend greatly affects system performance. They are also rust-resistant, unlike galvanized sheet metal ductwork.


Sheet metal air duct is the most common type of ridged air duct and is constructed of galvanized steel or aluminum. Aluminum, in particular, is relatively light and easy to install but needs to be thick enough to avoid getting crushed if someone walks on it. Their non-porous surface means they are unlikely to develop harmful biological growth.


Fiberglass Duct boards are made from high-density fiberglass boards. Whether on the interior or exterior of the system, a fiberglass lining insulates the ducts to prevent heat loss or condensation. Fiberglass lining also provides sound attenuation, reducing the noise of the HVAC system.


Fiberboard air ducts are constructed with boards of compressed resin bonded inorganic glass fibers. They have a foil face on the outside that serves as the air barrier and water vapor retarder. The interior of the fiberboard air duct is sealed to prevent fiberglass fibers from entering the air stream. Fiberboard air duct also provides acoustical and thermal benefits, and are typically the most inexpensive air duct systems to install.

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