The ductwork is an extremely important part of both residential and commercial HVAC systems. But are there any major differences between the ducts used in commercial buildings and those installed in our homes?
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The main difference between residential and commercial ductwork is that the latter is a lot larger in size as, in some cases, it would have to serve dozens of spaces. Consequently, the installation and maintenance of commercial ductwork would be more complicated and expensive.
What are the different types of ducts and why are these elements so important? Let’s find out!
What Is Ductwork?
Ductwork is a series of sectioned pipes that allow either cooled or heated air from the air-con or furnace to travel throughout the building. The ducts, together with the heating and cooling unit are basically your house’s HVAC (Heating, Ventilation, and Air Conditioning) system.
You can think of an HVAC system as the circulatory system in the human body. The thermostat that controls the whole system is the ‘brain’, the furnace and the air conditioner are the heart, while the ducts are the blood vessels.
Just like in our organism, the heating and cooling system has the ‘veins’ and ‘arteries’ – the return and supply air ducts. The latter send the heated or cool air into the house, while the return ducts bring the air from the rooms into the AC or furnace.
Together with a properly functioning heating and cooling system, the ductwork will help you keep your home at a comfortable temperature at all times.
Read: How To Locate HVAC Dampers In Ductwork?
Why Is Ductwork Important?
The ductwork that has been correctly sized and installed has quite a few benefits:
- The right type of ductwork will reduce the strain on your heating and cooling system. This, in its turn, leads to energy savings and will help prolong the life of your HVAC equipment
- You can choose to install various additions in the ductwork (like filters or UV lights, for example) that will make the air circulating throughout your house cleaner
- A correctly operating system of ducts will also increase the overall comfort level of your house as you’ll be able to enjoy consistent temperatures
However, if the ductwork wasn’t installed properly and if it’s too small or too big for your house, then your home will have hot and cold spots, the quality of the air is going to decrease, and your HVAC equipment might be forced to work harder (this leads to higher energy bills and frequent breakdowns).
In a nutshell, your ductwork is just as important as your furnace or air conditioner.
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Read: Does Ductwork Need To Be Sealed?
What Are the Types of Ducts?
There are two main types of ducts – flexible and rigid. The type that is going to suit your specific case should be determined by an HVAC technician as both flexible and rigid ducts have their own pros and cons and areas of use.
Flexible Ductwork
In the majority of cases, this type of duct is made of steel wire helixes. Just as the name suggests, these ducts are flexible and they are incredibly easy to install.
Flexible ductwork is also one of the cheapest types and they are perfect for extremely tight spaces where rigid ductwork simply can’t be installed. You can easily bend the flexible ducts around various structures.
By the way, flexible ducts are usually made out of plastic which means that no harmful particles will be released into the air (like in the case with fiberglass). Moreover, this material is less likely to become rusty and moldy.
The main disadvantage of flexible ducts is that they might develop bends and kinks that will restrict airflow and make your HVAC system work a lot harder.
Read: Should Ductwork Be Insulated?
Rigid Ductwork
Rigid ducts come in different sizes and can be made out of different materials. The cylindrical or rectangular ducts come in three types.
- Sheet metal ducts are relatively easy to install and are incredibly lightweight. They are also mold-resistant and durable. The only downside is that sheet metal ducts are more likely to develop leaks in the places where two sections get joined.
- Sheet metal ducts that are lined with fiberglass are called ‘fiberglass-lined ducts’. Such a layer of insulation reduces heat loss and makes the ducts more soundproof. Unfortunately, the material can start to degrade over time and the fibers that have been released into the air pose a health risk.It is also more difficult to keep such ducts clean and, as a result, fiberglass-lined ducts can easily become a breeding ground for bacteria, mold, and mildew.
- Finally, fiberboard ducts that are made out of compressed fibers. The actual boards are covered in foil – this means that you wouldn’t have to add insulation to the ductwork. Fiberboard ducts are also the cheapest among all the types mentioned.The main downside is that these ducts are prone to mildew and mold growth. Moreover, the roughness of the inside of the ducts causes friction and this diminishes the overall efficiency of the heating and cooling system.
The Difference Between Residential and Commercial Ductwork
The most important difference between commercial and residential ductwork is that the former is a lot larger than the latter. That is because commercial ductwork has to serve dozens or even hundreds of spaces.
Because of the size difference, the installation and maintenance costs will be different as well. There is typically a whole HVAC team or at least a few technicians that are responsible for the upkeep of the ductwork in a commercial building.
When it comes to the most commonly used types of ducts, sheet metal ducts can be found in the majority of homes, while fiberglass-lined ducts are quite popular in commercial buildings as they help reduce the sound of the HVAC system.
Read: Should Ductwork Be Replaced After 20 Years?
What Is Ductwork Made of?
| Type of Ductwork | Material |
| Flexible ductwork | The only ducts that are not rigid are made out of a steel spring coil that is covered in plastic. |
| Sheet metal ducts | This is the most common type of ductwork and it’s made of aluminum or galvanized steel. |
| Fiberglass lined ducts | A fiberglass lined duct is a sheet metal duct that has an additional fiberglass lining either on the inside or the outside |
| Fiberboard ducts | The final type is made of fiberglass strands that are held together by resin. On the outside, the ducts are covered with foil for extra insulation. |
How Does Your HVAC Ductwork Work?
The ductwork is an essential part of an HVAC system. It is the main channel through which conditioned air travels to the various rooms in your house.
The ductwork consists of the large main trunk and the pipes that connect to the trunk and then travel to the different rooms. Some HVAC systems might also have other ducts that deliver air to specific places in the house. A thin, vertical duct, for example, is called a ‘stack’ and it allows air to travel vertically through a thin wall.
Duct transitions are another important part of the ductwork. All the ducts need to be properly connected, in order to be able to fulfill their functions. The trunks and pipes can be connected by cleats, turning vanes, take-offs, and other elements.
The ductwork also has two plenums. The HVAC system will fill the supply plenum with conditioned air that is then sent through a series of ducts. As the ‘new’ air enters the room, it pushes the ‘old’ air into the return ducts, and the air travels back to the return plenum. The returned air is then sent either outside or back into the system through a filter.
How Should Ductwork Be Installed?
There are a few basic rules that you should bear in mind when installing ductwork:
- Always remember that hot air rises and cold air falls. For example, for your air-con to work properly, the large ducts that will be carrying the air back to the unit have to be installed high up on the wall (on the upper floor).
- Your ducts should run as straight as possible. The more turns, the slower the air is going to move.
- Ensure that every register is fed directly from the trunk line or the central unit.
- When you have to make a turn, use only the fittings that are designed for this specific purpose.
- Insulate the ducts that are running through unheated spaces.
Read: Ductwork Insulation: Everything You Need To Know
Common HVAC Duct Problems
- Poor design – if your ductwork has too many turns and covers a greater distance than it actually should, then your HVAC system will be less efficient and your energy bills will be higher
- Improper insulation – if the ducts aren’t insulated correctly, a lot of air will simply escape
- Dirty ducts – bacteria, mold spores, and dust will get recirculated in the system and will worsen your home’s air quality
- Leaky ducts – if your ductwork has leaks, you will be losing a lot of conditioned air and various pollutants would be able to enter the ducts
Why Is It Important to Seal Ducts?
There are quite a few escape routes for the conditioned air that is traveling through your ductwork, starting from unsealed connections and ending with holey tape around the plenums.
A lot of homeowners have leaky ducts, but not all of them understand how many benefits duct sealing has.
- Properly sealed ducts allow your system to work efficiently (just as it should)
- Your HVAC system wouldn’t have to work as hard to maintain the desired temperature, this will result in lower energy bills
- The fewer leaks there are, the less dirty air would be able to enter the ductwork, which means better air quality in the house
- If less dust will be entering the ductwork, your evaporator coil will stay clean for longer
How to Seal Ducts?
If you want to seal your ducts, you are basically left with three options:
- To use duct sealing tape
- To use a mastic duct sealant
- Or to choose an Aeroseal duct sealant
How Long Does Ductwork Last?
The ductwork is designed to last for around 10-15 years. If your ducts are older than that, then the chances are high that there are major issues with this part of your HVAC system (for example, the ducts have holes in them or they have collapsed altogether).
Signs You Need Air Duct Replacement
There are a few tell-tale signs that it’s time to replace your ductwork:
- Higher than usual energy bills
- Strange noises
- Uneven cooling or heating
- A dusty home
- A musty smell
- Issues with pests
- Tangled ducts
You might also want to consider replacing the ductwork if it’s over 15 years old.