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What is duct and types of duct

What is duct and types of duct


What is duct and types of duct

In a HVAC system, ductworks and insulation is one of the essential part to consider. A proper ductwork and insulation will save users lots of costs for electricity and maintenance. Ducts are used to distribute air for various air conditioning systems and ventilation systems. Many people are confused about the duct types. Actually, ducts used for HVAC systems and home ventilation systems are different in many aspects. So today we’ll take a look at different types of ducts.


Flexible Ducts

Flexible ducts are one of the most common used ducts in an HVAC system or in a home ventilation system. They are relatively cheap, light in weight, and easy to install. So it’s not necessary to use a CNC duct fabrication machine. They are often insulated with fiberglass insulations when applied for air conditioning. However, flexible ducts which have no insulations are only used for ventilation such as toilet exhaust.


Flexible ducts are common in use for their low prices and easy installation. However, the main disadvantage of flexible ducts is high pressure drop and low airflow. Because flexible ducts are flexible, they are prone to sharp bends. If a flexible duct is bent too much, it can block the airflow entirely. Hence, it is advisable that a flexible duct should not be more than 2.5 meters in length.

 hvac flexible duct


Rigid Ducts

The second commonly used type is rigid ducts, which are also known as sheet metal ducts. Rigid ducts often are made of sheet metals which are usually galvanized steels. Rigid ducts can be made in square, rectangular or round shapes. A CNC duct fabrication machine is needed to speed up the fabrication process.


Square rigid ducts are more economical to produce than both rectangular and round rigid ducts. Because the total surface area needed lesser. Therefore, the material used is lesser. In HVAC, main ducts and branch ducts are usually rigid ducts. They are more likely in a rectangular shape rather than in a square shape. Even though the cost is higher. Round ducts are more preferred when installed below the ceiling especially when the interior aesthetic requirement is high.


If rigid ducts are used for air conditioning, they must be insulated to prevent condensation. People use either fiberglass insulations or cross-linked polyethylene for insulations. If it is the former, the outer appearance will be in silver color. Otherwise, they may look grey in color.



insulated rigid ductwork

Pre-Insulated Ducts

Pre-insulated ducts are made of either polyurethane (PU) or polyisocyanurate (PIR) material. They have been launched in the market for years, but the application rate is rather low. Because the material cost is higher than the other types.


However, pre-insulated ducts have many benefits that other materials don’t have. Firstly, they have a very high efficiency. Pre-insulated ducts are joined by glues and clips, sort of like a slot-in. Such a jointing method has a much lower leakage rate than both slip & drive joint and TDC joint.


Secondly, pre-insulated ducts are pre-insulated and hence, they do not require further insulations on-site which enable them to be installed very close to the soffit slab or even flush with the soffit slab. So, pre-insulated ducts occupy less space than rigid ducts.


Last but not least, pre-insulated ducts are much lighter than traditional galvanized iron rigid ducts. Thus, the installation process is faster. If you use a CNC duct fabrication machine to do the measuring and cutting, it will be even faster. There are more and more HVAC contractors willing to use pre-insulated ducts for their projects. For big HVAC contractors, they often have many projects on-going, to speed up the fabrication process, they often buy CNC duct fabrication machines to replace man cutting. A CNC duct fabrication machine is fully automatic, which cuts phenolic boards fast and precisely. The application of CNC duct fabrication machines has revolutionized the duct industry since its launch.


 phenolic boards

In conclusion, if your budget is enough, we suggest you to use pre-insulated ducts for better efficiency, fire-proof, and easier fabrication. If you budget is limited, then use rigid ducts as a second choice. If it’s for home ventilation, and you have very small budgets, then use flexible ducts might also work.

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