(707) 800-6287 |  Sonoma Napa and Marin Counties

Whether you are installing new ductwork in your building for heating and cooling purposes or hiring an HVAC contractor to handle air duct cleaning, it can be useful to know as much as possible about the different types of commercial air duct designs. In the case of a new duct installation, knowing about different types of ducting solutions will help you select the right one for your building. In the case of duct cleaning, knowing what kind of duct setup you have in your building will enable you to provide your HVAC contractor with information that will help them deliver quality services. In this post, we will discuss the most common types of commercial air ducts.

Types of Commercial Air Ducts

Woman holdin air duct placed inside roofThe two most common types of commercial air ducts are metal ducts and flexible ducts. Metal ducts consist of rigid sheet metal ductwork, usually crafted from galvanized steel or aluminum. These ducts can exist in a variety of sizes and shapes, including round and rectangular. They are known for their durability and longevity and are an effective means for conveying airflow long distances throughout a building. These features make rigid sheet metal ducts the bread and butter for most commercial ductwork systems.

Flexible air ducts, as their name implies, do not have the same rigidity as sheet metal ductwork. These ducts are usually circular and are known for being lightweight, well-insulated, and easy-to-install. They can be made from a variety of different materials, including rubber, stainless steel, PVC, polyurethane, and silicone. These types of ducts are typically best for shorter runs. They deliver the best airflow when kept relatively straight, though some of their appeal is that they can bend easily—thus making it easy to direct the air precisely where it needs to go.

Many commercial HVAC systems combine these two types of ductwork. Two examples are the trunk and branch system and the radial system.

  • Trunk and branch systems: Trunk and branch HVAC systems (also known as extended plenum systems) start with a long piece of rigid metal ductwork that is connected directly to the heating or cooling equipment. This ductwork is the “supply trunk” or “plenum” for the system, in that it is the central hub of the warm or cool air coming into the ductwork. Several other ductwork runs connect directly to the main trunk and then spring off toward different parts of the building. These “branches” deliver the air to vents or registers throughout the building. Smaller branches include air dampers, which help keep too much air from circulating in those directions. The branches are usually rigid sheet metal ductwork but can also be flex duct. This type of system is highly effective and efficient for distributing conditioned air to all different parts of a commercial building. In some cases, the plenum can be reduced in size/diameter further down its run, to make sure that airflow velocity/air pressure remains even as air branches off in all different directions. This variation of the system is known as a “reducing plenum system” or a “reducing trunk system.” 
  • Radial systems: Radial systems aren’t so different from trunk and branch systems. In fact, radial ductwork designs are often referred to as a variation on the trunk and branch design. There is the main supply plenum that is linked directly to the air conditioning and/or heating equipment. As with a trunk and branch system, numerous branch ducts connect to this supply plenum and carry air off to different parts of the building. Instead of resembling a tree, though, a radial system sees the branch ducts—almost always flex ducts—arranged in a radial pattern and running off in all directions. The plenum is not nearly as long as in an extended or reducing plenum system.

While there are other types of ductwork systems, these two are typically considered to be the most suitable for most spaces.

Dust Mites in your HVAC Ducts

Air Duct Cleaning for Different Types of Duct Systems

Regardless of whether your building uses rigid metal ductwork or flexible ductwork, and irrespective of whether your system is a trunk and branch system or a radial system, know that regular air duct cleaning is a must. Experts typically recommend that you have your building ducts cleaned at least every two years, if not annually. Some ductwork installations demand more frequent cleaning. For instance, to retain airflow through an extended plenum system, you might want to adopt a more regular cleaning strategy. All ducts, whether rigid sheet metal or flexible ductwork, build up dust, dirt, hair, and other debris over time. Regular cleaning appointments will keep your ducts clear, maximizing the efficiency and cost-effectiveness of your building’s heating or cooling system. Furthermore, regular duct cleaning can eradicate mold growth, mildew, and other issues that may drastically and negatively impact the air quality in your building.

If you are sure what type of ductwork your building has, ask your HVAC contractor to give you some details when you call for an air duct cleaning appointment. Knowing this information will help you plan the appropriate maintenance and cleaning schedule for your ductwork system.