Close this search box.

Round Spiral Ducts for HVAC: What You Need to Know

round spiral ducts for hvac what need to know

The duct network, along with the ventilation system, is one of the most important parts of the HVAC system. Although not as technologically inclined as other components, these networks are stills necessary. Thus, it may come as a surprise when not many people are intimately familiar with the ins and outs of a duct system unless they work in the HVAC industry. Consequently, not many people are aware of the round spiral ducts either.

Ductwork and ventilation systems are an important part of any HVAC system. It is responsible for transferring air to and from different places. Air conditioning, heating, and dehumidification all depend upon the ducts to move the air from one point to the air. It comes in different shapes and sizes, and the one that is under discussion here is the round spiral duct.

Here is everything you need to know about round spiral ducts for HVAC.


Ductwork is the system of ducts that interconnects the HVAC system to the different parts of your home or building. Its main job is to transfer air from HVAC to, again, the building. The network includes ventilation, cooling, and heating, connected by supply and return ducts.

The entire system is made up of metal tubing of different shapes and sizes depending upon the specific application and requirement. When it comes to shape, there are three classifications; rectangular, circular, and oval, which is a compromise of the first two shapes.

What Are Round Spiral Ducts?

One thing that needs to be cleared is this: spiral ducts and round spiral ducts are the same. A Spiral is a continuation of round curves. When you search the internet for round spiral ducts, you will either get round ducts or spiral ducts. Both refer to the same things, surprisingly.

Nevertheless, spiral or round spiral ducts are rigid steel pipes in a spirally wound shape. There are different materials that can be used for its construction and making, including aluminum, copper, stainless steel, and the most common one, galvanized steel. A male coupler is used to connect two spiral ducts, as it has a female ending.

However, the word duct is very limiting. When it comes to spiral ductwork, there are many more things included, in addition to simple pipes and fittings. It is a complete ventilation system, which can include the following components depending upon the requirement and nature of the project.

  • Ducts and fittings (bends, couplings, reducers, t-pieces, end caps, etc.)
  • Sound attenuation products (sound attenuators themselves, duct insulation, flexible duct connectors)
  • Airflow regulation products (air dampers, CAV, and VAV regulators)
  • Suspension and fixing products (threaded rod, clamps, support brackets, rivets, self-drilling screw, rivets, sealing tape)
  • Fire protection products (fire dampers, smoke dampers, fire-rated air valves)
  • Finish-trim products (diffusers, air valves, louvers, etc.)

Benefits Of Round Spiral Ducts:

Reduced Air Drag And Friction:

There are numerous benefits of round spiral ducts. First and foremost: it comes with an airflow with negligible drag and air resistance. Which is perfect for commercial and industrial purposes; the workload is heavy enough that other types are not really suitable for them, so round spiral ducts are the perfect choice for such areas.

Increased Efficiency:

The reduced air drag and friction also yield another advantage: efficiency. To explain it properly, research confirms that round spiral ducts can transport air with an almost negligible amount of friction. The friction loss in such shapes (round) is due to having the greatest cross-sectional area.

Reduced Energy Costs:

With reduced friction and air drag, the energy and fan horsepower spent to blow the air into the ducts also reduces. Thus, the associated energy costs are also reduced significantly.

Lightweight Without Losing Rigidity And Strength:

For air transportation, round ducts are often preferred over other types. Their uniqueness stems from the fact that round spiral ducts, especially galvanized steel ones are lightweight. It is lightweight, but the decrease in weight in no way compromises the rigidity and strength of the pipe. So for long ductwork, this is an obvious choice.

Low Costs:

The cost will decrease as less material is required to make ducts. The cost will also reduce when it comes to supporting accessories. Round spiral ducts are lightweight, so not much is required to support them when these pipes can span long distances without any problem. And finally, round spiral ducts made of stainless steel can resist corrosion due to enhanced resistance, which makes them the obvious choice for factories or industrial complexes that are frequently exposed to harmful chemicals.

Longer Length:

Round spiral ducts are lightweight and available in longer sizes too. The standard size for these types of ducts is around 3 m, whereas rectangular ducts can rarely go beyond 1.2 m without causing problems. In other words, spiral ducts can span long distances without any fuss.

Reduced Noise:

Well, the friction and air drag is reduced to vast amounts, right? This brings an unintended advantage: reduction in noise.

Need For Cleaning And Maintenance Is Not High:

Spiral ducts are round in shape. This shape gives a lot less surface area for dirt and dust accumulation. Thus, the need to clean the duct frequently would go down a lot, along with maintenance. This would also result in having a healthy indoor environment with good indoor air quality. There would be not much place for bacteria to breed in, so air quality would drastically improve.

Less Leakage:

Most of the advantages of round spiral ducts are consequences of each other. These are lightweight ducts. Thus, they can be fabricated into longer lengths. The longer length would come with fewer joints, which are a hotspot for any leakage. Decrease the joints, and leaks also decrease. In other words, a properly engineered round spiral duct would have a 1% chance of a leak occurring in its lifetime.

To summarize:

Here are the advantages of round spiral ducts in a nutshell.

  • Decrease in energy usage for heating and cooling
  • Lower fan energy use
  • Reduced air leakage
  • Low costs for installation in comparison
  • Less material is required for usage
  • Attractive in appearance and looks
benefits of spiral ducts

Types Of Round Spiral Ducts:

Round spiral ducts are categorized into two different types. This classification is done on the bases of the materials the duct is made out of. For some, this may be strange. However, the specific material used to build the duct has a lot of significance in the ductwork. It all depends on applications and requirements. This material is the distinguishing element here.

Here are the two types of round spiral ducts.

Galvanized Steel Spiral Ducting:

Galvanized steel is the most common material used to make round spiral ducts. This makes galvanized steel ducting the most common type. Its advantages include low cost, lightweight, and rust protection. The rust protection comes from zinc coating, which also gives it the added advantage of additional places for installation. In other words, galvanized steel ducting can be installed inside and outside.

Stainless Steel Spiral Ducting:

Galvanized steel is not the only option. But steel is, due to its hybrid properties, as the material comes from a mixture of different metals. Thus, stainless steel spiral ducting is another type. However, it is not as common as the first type. It is only used for specific requirements. For instance, in a place where chemical exposure is common for machinery, galvanized steel would easily corrode when exposed to specific chemicals. Stainless steel, on the other hand, has an amplified resistance against harsh chemicals and resulting corrosion, so this type is used.

The Materials Used For Making Round Spiral Ducts:

Here are the three most common materials used to make round spiral ducts.

Galvanized Steel:

Once again, the most common material to make round spiral ducts is galvanized steel. This is an ideal material for ductwork due to its lightweight, corrosion resistance, and ability to withstand higher temperatures.


Aluminum is the most lightweight option out of the bunch. In addition to that, it also retains its high strength at such a low weight. Due to these reasons, aluminum spiral ducts can span longer distances with many support accessories.

Aluminum also comes with flexibility. This implies that the material can be stretched and bent without losing elasticity to a great limit. So this is an air duct that is elastic but also will hold an airtight seal regardless of how much it is stretched. Aluminum spiral ducts are commonly used in factories.

Stainless Steel:

Stainless steel comes with increased resistance to corrosion and the ability to withstand temperature. As it can withstand harsh substances without corrosion, spiral ducts made of this material are commonly used in laboratories. Its sanitary benefits are numerous, so it is the perfect choice for such a place.

It can be said that spiral ducts made of stainless steel come with the advantages of both previous materials and amplified ones.

Round spiral ducts
Round spiral ducts

Size Of Round Spiral Ducts:

The most common size of round spiral ducts would be 80 mm to 710 mm in terms of diameter. But that is not really a standard. You can get ducts of diameter all the way up to 1600 mm. This is not that astonishing, as some companies extend that to a whopping 2200 mm diameter.

The length is an entirely different matter. Usually, the standard size of galvanized steel is 3 m. But the manufacturer can change that if the situation calls for it. As for the thickness, it can be anywhere from 0.4 mm to 3 mm for galvanized steel.

Diameter Range: 80 mm to 1600 mm

Standard Length: 3 m

Thickness Range: 0.4 mm to 3 mm

Material: Galvanized steel, stainless steel, mild steel, Aluminum, Copper

Diameter (mm)                                 Thickness mm(G)
80 to 2500.50 (26G)
275 to 3500.50 (26G)
375 to 6000.63 (24 G)
650 to 9000.80 (22 G)
950 to 12501.00 (20 G)
1300 to above1.25 (18 G)

Applications Of Round Spiral Ducts:

Round spiral ducts are the most common choice when it comes to the ventilation system. For commercial and industrial systems, that is, not for residential. This is because this specific type of duct is used for transporting large volumes of air from one place to another in a building. There is no such requirement for such application in a residential area, but plenty in commercial and industrial complexes. Thus, most of the applications of round spiral ducts are in the latter 2 fields.

Additionally, as mentioned earlier, some spaces have frequent chemical exposure. Even if humans don’t frequent such places, machinery is still there, and it has to be up to par to resist the corrosion from such chemicals and do its own job. So having ductwork that can corrode and melt away in such harsh conditions can throw a wrench in the routine. Hence the need for spiral ducts.

Here are the places where it can be used:

  • Office buildings
  • Factories
  • Industrial complexes
  • Workshops
  • Pools
  • Restaurants
  • Commercial kitchens
  • Retail outlets
  • Shopping complexes

And here are some general applications of round spiral ducts.

  • Air Conditioning (High Pressure & High-Velocity Distribution System)
  • HVAC applications (in industries & tunnels)
  • Can be fabricated as flat oval duct when needed
  • Dust removal
  • Fume exhaust
  • In grain handling
  • Material conveyance
  • In architectural applications (void forming tubes)

How Round Spiral Ducts Are Made?

Making Round Spiral Ducts: A Summary

A special machine called tube formers is used for the construction of spiral round ducts. These types of ducts are made out of wide spirally rolled steel metal sheets of size ranging from 137 nm to 140 nm. It should be remembered that experts recommend manufacturers buy metal sheets or strips themselves. This should be done so that the material would have an exact dimension tolerance. If precautions are not taken, even a small margin of error can cause a lot of damage. The manufacturing machine or the spiral duct machine would close the lock seam improperly.

Finally, in the end, there would be another machine called a slitting machine that would cut out strips from large steel coils. These narrow steel strips would be cut from large coils of width ranging from 1250 mm to 1500 mm.

Fabrication And Making Of Round Spiral Ducts:

The initial process depends upon the type of material being used for making the duct. All the above-mentioned materials, galvanized steel, aluminum, and stainless steel, are made in different ways. It’s only when it comes to the second part of the process that all three are the same.

First, the master coils are created from metal sheets, the process depending on the material. Once these are done in the mill, the coils are sent to processing plants to change into narrower coils called slit coils from the master coil with a slitting machine.

Afterward, instead of sending them to another plant to make the duct, these coils are directly sent to the customers. Once there, they are processed according to the required specifications, creating spiral ducts. Finally, the fabrication process occurs.

The slit coil is placed on a coiler. It is then sent through a rough leveler, which flattens out the material. Finally, an edge trimmer does the next step to create a strip. The resulting strip is now subjected to the welding stage (inner and outer welding). This will force the material into a circular shape, forming a spiral. Now that the spirals are formed, the edges are pinched or welded together, creating a duct piece. Finally, the last step would include cutting the duct piece to the desired length, which is then thoroughly tested and inspected. Finally, it is sent to the installation place to affix it to the duct network.

spiral duct stack
spiral duct stack


Do round spiral ducts need to be insulated? The answer is yes, yes, they do. It is true that these ductwork come with heightened resistance to corrosion and harmful chemicals, but the need for insulation is still there. And there would be two primary reasons for that: controlling thermal and acoustic conditions.

In the case of thermal control, the insulation is done to keep the air within the duct. This would result in improving the efficiency of the duct. Less energy would be spent to transfer the treated air in the ducts with the help of insulation. Additionally, in humid temperatures, condensation will almost always be present on any part of the duct that has a temperature lower than the dew point. That moisture brings along with it problems like mold growth, bacteria, and dripping on the floor. With the help of insulation, the condensation on the duct can be prevented.

Acoustical control might not be something that engineers really look for when it comes to ductwork, but it helps. From a technical point of view, there is no advantage to that, but it helps reduce noise, which improves the indoor environment.

Comparison With Other Shapes:

It is a fact that round spiral ducts would always come on top when compared to rectangular ducts.

First of all, it’s lightweight. This comes with the added advantage of increased efficiency, reduced friction, air drag, energy cost, and relevant cost. Moreover, compared to rectangular ducts, the material required to make the ductwork would be way less and needs a lot fewer supporting accessories.

An added benefit of less surface area also reduces dust and dirt accumulation. So there went cleaning and maintenance costs. To summarize, compared to rectangular ducts, round spiral ducts will cost you 50% less. And the chance of leakage is also low due to fewer joints.

Frequently Asked Questions:

Q: Is round spiral ductwork better than rectangular?

Ans: For high-pressure HVAC systems, spiral round ductwork is undoubtedly the superior, no, best option. As we have explained earlier, spiral ducts come with significantly decreased levels of friction and air drag. In comparison to them, rectangular ducts are not really as efficient with airflow. This type would increase more pressure on the system, which an already highly pressured. An HVAC system would not be able to sustain.

Q: When would you use a spiral duct?

Ans: The best use of spiral ducts would be, again, in high-pressure HVAC systems where ducts have to carry large volumes of air from one place to another. Its residential uses are minimal because average ductwork is enough to take up the burden. However, the commercial and industrial field is on a whole different level, where a round ductwork spiral would be the best choice.

Q: What is the most energy-efficient shape of duct?

Ans: That would be the round and spiral-shaped ducts. These shapes come with the greatest cross-sectional area, which decreases a lot of air drag and friction. As such, the amount of energy and fan horsepower required to push the air would not be very high, making these shapes the most efficient when it comes to energy conservation.

Q: Is spiral duct more expensive?

Ans: Compared to what? Other shapes or something else? That is an important distinction. But let’s go point by point.

Spiral ducts are the most efficient and conserve energy. So energy costs are low. Second, it’s lightweight. Thus, it does not need many support accessories, saving money in that regard. Third, it can span long distances without any problem, so less material is used in making these ducts. Conclusion? Round spiral ductwork is a lot cheaper, especially when compared to rectangular ducts.

Q: Does the spiral duct leak?

Ans: Interestingly enough, spiral ducts have a less than 1% chance of leakage if engineered correctly. It can be attributed to the fact that these ducts have way less joints than any other type. And joints are hotspots for leaks.

Q: What is a double-wall spiral duct?

Ans: Double spiral ducts are exactly what the name suggests. In short, it comprises two walls. The first one, the visible duct, is the larger part. The second is the inner spiral duct hidden behind the first one. The double-wall spiral duct has increased efficiency and ensures a consistent airflow temperature during delivery.


HVAC is a vast industry that has a lot of applications. These applications are spread all over the world in many industries. For many applications, existing solutions do not work, so many turn to fabrication.

Our company, SuperAir, provides a variety of HVAC accessories. In addition to that, we also provide other solutions and services like fabrication. If you and your business are facing any problems in this regard, contact us ASAP to take advantage of our high-quality services.

To look at our catalog, visit our website right now.

Contact Us to Find More Products

Should you have any inquiries about HVAC, or get our latest catalogs, please leave a message below and we will contact you within 24 hours.

Ask For A Quick Quote

We will contact you within 1 working day, please pay attention to the email with the suffix “”