What Are The Three Types of Air Ducts?

Whether you adjust the temperature manually or use a smartphone to turn on your HVAC systems, the thermostat is where most homeowners interact with their indoor air. Within your home there is a vast network of components driving fresh air in and stale air out of your home. You likely change the air filter regularly and clean around the air conditioner, furnace and air vents, but do you ever consider the ductwork that moves all the air throughout your home?

Understanding how ductwork moves air within buildings helps you learn how to improve indoor air quality and lower your energy usage. There are two primary types of air ducts within your HVAC system. Air ducts that move treated air into every room are called supply ducts. These air ducts emerge at vents on floors, walls, and ceilings. When fresh air enters through supply vents stale air leaves the room through return ducts. Return vents are often larger than supply vents and help keep air pressure stable within your home.

Shape of Ductwork

Ducts hidden behind walls, floors, and ceilings are designed to optimize airflow and provide efficient heating and cooling within buildings. There are three common shapes of air ducts: round, rectangular, and oval. Each shape has distinct advantages and disadvantages.


Round ducts are the most common shape of ductwork within homes. Round ducts use less material and can be installed quickly because pieces are easy to join together. These factors mean round ductwork is often the most economical to install. Increased airflow through round surfaces reduces friction. This quality reduces noise pollution when HVAC systems are running. The primary disadvantage of round ductwork is height requirements based on their placement.


When space is limited rectangular or square ductwork is used. While rectangular ductwork uses more material, the design provides more volume for airflow. For low-pressure HVAC systems, this increased airflow is a major advantage. When ductwork is exposed within a business or retrofitted spaces rectangular ductwork is also aesthetically pleasing. Vibration within rectangular ductwork creates more noise pollution than round or oval ducts. Rectangular connections are not as seamless as other shapes. Energy can be lost due to leaks and poor connections within the ductwork.


Oval ductwork blends the best qualities of round and rectangular ducts. Although less common than other shapes, oval duct systems are highly efficient featuring a low profile, high flow, and curved surfaces to reduce noise pollution. The connections of oval ductwork are seamless which helps weatherproof ductwork.

Type of Duct Systems

The shape of ducts is just one factor in understanding how your HVAC system performs. There are three common types of duct-flexible, rigid, and semi-rigid. Each type of duct system uses various materials to suit unique applications. All HVAC system installations, repairs, and maintenance should be performed by a trained professional. When the incorrect type of duct and materials are used the indoor air quality suffers, energy bills increase, and equipment can even be damaged.

Flexible Ductwork

This type of ductwork suits installation in difficult and hard-to-access areas. Flexible ductwork can be adjusted easier than other designs. However, flexible ducts must be installed carefully. When properly secured and adjusted, airflow through flexible ductwork is efficient. The advantage of flexible ductwork is the ease of installation and lower costs but poor installation is a major disadvantage. Improperly installed flexible ductwork may sag, snake and kink. These issues compromise airflow which impacts energy bills and may result in more frequent repairs to expensive equipment. If you see loose, sagging, or damaged flexible ductwork, you should contact our team to assess and correct the issue.

Rigid Ductwork

Manufactured in a range of sizes and materials, rigid ductwork usually describes insulated fixed pieces. These pieces are joined using special bends like pipes for plumbing. Rigid ducts are durable and highly efficient. Offered as sheet metal ducts, fiberglass lined air ducts, and fiberboard air ducts, rigid ductwork is lightweight and strong. This helps optimize efficiency and maximize lifespan. Since rigid ductwork does not bend, the planning and installation are extensive. Rigid ductwork is often more expensive to install because it requires high levels of skills and experience to install this type of ductwork. Like all ductwork, rigid ducts should be installed and maintained by professionals.

Semi-rigid Ductwork

Considered by many people to be the most dependable type of duct for ventilation, semi-rigid ductwork provides a zero leakage ventilation system when installed by properly. Semi-rigid ducts are usually installed quicker than rigid ducts which save labor costs. Some designs of semi-rigid ducts can be switched from round to oval shape without losing performance maximizing efficiency. This quality also helps installers design efficient systems even when height is restricted.

How to Maintain HVAC Duct Systems

Regular inspections and cleaning of air ducts improve air quality and optimize the efficiency of central air conditioning and heating systems. Dirty, blocked or damaged air ducts are often the cause for uneven heating or cooling within your home. During an inspection of your duct system, professional technicians will visually inspect for damage, leaks, and wear. Flexible ducts and semi-rigid ducts are more prone to crushing and other damage when exposed in basements, attics, and crawlspaces. HVAC technicians will also test the pressure within your system. Leaks within ductwork can compromise performance and efficiency. Finally, cleaning ducts helps remove dust and debris. Clean air ducts help improve indoor air quality for family members with allergies, asthma, and other respiratory issues.

Contact Redman Services

Redman Services is always prepared to answer your questions. If you have questions or concerns about your air ducts or the performance of your HVAC system, you can depend on our team to provide a solution. Call on your hometown hero for all your heating, cooling and plumbing needs.