Round vs Square Ductwork

Whether it’s in your home, a residential building or a commercial office space, ductwork is designed to contain air as it is conveyed through a HVAC system

However, the world of ducting is varied and diverse with rectangular ducting and round ducting being the two main contenders.

If you’re about to install an HVAC system and you aren’t sure of which ducting you should use, the article below offers more insights into the advantages and disadvantages of both. It also focuses on cost, energy efficiency, least resistance to air flow, and the primary differences between the two. Ready to discover more? Let’s begin.

What are the advantages of square ducts?

When we talk about rectangular ductwork or square ducts, it’s important to note that this type of ducting can also be referred to as a flat duct. They are most commonly used in spaces that are quite limiting and which do not allow for the height of round ducts. Some of the advantages of square ducting are:

• Neater and easier connections between the fans – equipment and the main duct
• It requires less space and takes up less height, making it easily adaptable
• It can be more suitable for low-pressure systems
• It can be exposed in places, such as warehouses, lofts and bars
• It is easy to fabricate into flat surfaces for a trunk-and-branch design or branch tap-ins
• It is easy to ship when broken down

What are the disadvantages of square ducts?

Using a square duct is not always the ideal solution though. In some cases, it can be problematic. This means that it comes with certain disadvantages, which may include the following:

• They allow for more noise to escape from the duct, not always effective for a work environment
• Their installation costs can be higher than round ducting
• It is usually limited in terms of length, which results in a greater number of joints
• It is known to leak more at the joints than round ductwork
• Flat ducting may need to be reinforced
• It’s possible that due to static pressure, the sides can start bulging out

What are the advantages of round ducts?

Round ducting, also known as circular or spiral air ducts, are the more frequently encountered type of ductwork. These ducts come with a number of advantages, such as:

• Quick installation as it’s easy to join pieces together
• Increased and more efficient airflow
• Better for medium to high pressure systems
• Reduces leakages
• It is lighter in weight
• Less friction
• Lower costs for initial installation
• Does not require reinforcement bracing for supply systems
• Quiet environment, resulting in less noise pollution
• Available in longer lengths than regular ductwork

What are the disadvantages of round ducts?

Despite all their advantages, round ducts are not suitable for all places and locations. Here are a few reasons why:

• They take up more height and space than rectangular/square ducts and simply won’t fit in the environment
• It can be aesthetically unappealing and difficult to connect fan coils to the main duct
• Not efficient for low pressure systems

Is a round or square duct cheaper?

When it comes to choosing between a round or square duct, cost considerations will naturally enter the equation. In practice, the cost of round ducting systems is usually much lower and cost effective than rectangular systems by approximately 67%.

What is the most energy-efficient shape of duct?

The most energy-efficient shape of duct is usually round ductwork. However, you should consider other factors when determining energy efficiency such as static pressure, velocity of the air flow and movement within the duct and others.

Which shape of ducts provides the least resistance to airflow?

Square plastic ducting that experiences high velocities is much more likely to create pressure loss and noise problems, as opposed to round or flat-oval ductwork. However, because round ducting does not fully take up the available space like square ducting would, it is technically considered less efficient at maximising airflow.

What is the most common type of duct?

The most common type of duct is the round or flat oval type of ducting, which usually comes in longer lengths and which can be easily fitted into a number of different environments.

What are the differences between flat and round ducting?

Whether you call it spiral or round ductwork, there are important differences between flat and round ducting. Below, we explore these in more detail in table format for easier comparison:

Criteria	Round ductwork	Square ductwork
Materials	Galvanised steel and Stainless steel. Alternatively, it can be made from sheet metal, fibreglass board, or flexible wire and plastic composite material	⅓ more sheet metal than round ducts, alternatively, fibreglass board
Length	It can be made to any length that fits on a standard truck	Different rectangular ducting sizes can be split up and conveyed on a truck
Connections	They can be connected using flange-to-flange connections or with slip joints male connectors	Generally flanged and bolted together
Cost	Cost-effective solution because they require less sheet metal for the same flow rates	More expensive than round ductwork due to materials, insulation support and labour required for installation
Noise	Perform well with lower pressure drops, more rigid leading to lower vibrations, therefore, leading to less noise	Can be excessive if not supported properly
Leaks	Fewer joints mean fewer leaks. They are also easy to seal.	More joints can mean a higher number of leaks
Best for	Buildings with sufficient height for installation	Buildings with greater width to height restrictions
Maintenance	May require less maintenance	Require more maintenance for long-term heating and cooling

Conclusion

Choosing between square and round ductwork is an important consideration that you’ll need to make. Factors to consider when making your decision include how much space you have, whether you have exposed ducts, if your HVAC system is high or low velocity, performance, fabrication, installation, economics and acoustics.

If you need expert advice on this aspect, you can always count on the experts at Ducting Express to help you and lend you their professional opinion given your specific circumstances. Get in touch with us today!