A central heating and air unit is essentially the heart of a home’s HVAC system, but the ductwork in attics and crawlspaces is just as important. Whether you are planning on replacing old ductwork or building a new home, our guide covers all the basics. We’re going to discuss the types of air ducts commonly used in residential homes today along with the pros and cons of each style.
The Different Types of Ductwork
Most homeowners understand the basics behind ductwork as ducts simply ensure air travels where it needs to go. It moves cool or warm air created by an HVAC unit to areas inside a home and is commonly installed in attics, basements, or crawl spaces. While there are several types of ductwork available for residential use, all fall into one of two categories.
In most homes today, you’ll find at least some rigid ductwork. In older residences, it could be the only type used, and while aluminum is an option, galvanized steel is far more common and cheaper. This type of ductwork can be fabricated for custom installations and varies in both shape and size.
Rigid ductwork is a smooth surface on the inside and outside. This ensures that it is easy to clean and the surface itself makes it difficult for mold to take hold. While durable, and puncture-proof to a degree, this type of air duct is challenging to work within tight spots.
Flexible ductwork is on the opposite end of the spectrum as they consist of wire coils with a covering that’s typically made from plastic. This type of ductwork is the best choice for cramped spaces where metal air ducts won’t fit and are considered cheaper and easier to install by homeowners or professionals.
The advantage of using flexible ducts is their ability to bend and be used in tight areas. It also means less work for you or the HVAC professional installing the ductwork. On the downside, they can be punctured and you have to be careful with flexible vents that sag and avoid kinks with these ducts.
While there are only a few styles of flexible ductwork, Fiberglass Duct Boards and Fiberglass Lined Ducts are also used in commercial applications. Fiberglass is a proven insulator often used on the outside of metal air ducts, but you’ll find it inside fiberglass-lined ducts as well.
While an excellent insulator which is used to limit heat loss and is used to dampen noise in commercial space, these ducts can also harbor mold and require special cleaning. You’ll still find them in commercial buildings but not in many residential settings.
Square or Round Ductwork?
For decades, rectangular ductwork was commonly found in homes, but it’s not the only option available to homeowners or contractors today. Round ductwork is an alternative and commonly found in newer homes for a variety of reasons. It may not be the best choice for your situation, however, which is why you have to consider the pros and cons of square vs. round ductwork.
Sturdy and distinct, rectangular air ducts are often the best option for low-pressure HVAC systems in residential homes. These ducts can be fabricated in-shop or on a truck by contractors with a brake, but are typically considered harder to install than round ductwork.
Rectangular ductwork is heavier and there are more areas to seal due to how it’s fabricated. That means more rivets and joints in general, which can provide more chances of failure. The added difficulty can make installations take long, which results in an increased cost of labor as well.
Round ductwork is just as durable as its rectangular counterpart, but this type of ductwork is easier to manufacture with fewer seams by design. Round metal ductwork can be used for longer runs with fewer joints to restrict airflow, which makes them more efficient overall. There are two types of round ductwork as well with traditional and spiral which can be stylish when left exposed.
This ductwork shape is also considered lighter and easier to install by HVAC professionals. Oval ducts are in this class and perfect for narrow wall cavities, although they are technically just flattened round ducts. Round ducts are perfect for medium to high-pressure systems although they require more height to install compared to rectangular air ducts.
Ductwork Construction and Cost
As with other HVAC products and accessories, branding plays a part in the cost of new ductwork, but not as much as the thickness or materials used in its construction. There are standards with the thickness that are set by the SMACNA, otherwise known as the Sheet Metal and Air Conditioning Contractors National Association.
This organization sets standards that manufacturers' products use when producing sheet metal ducts. The standards for welded ductwork are different from SMACNA air ducts, however, and the most common thickness carried by local hardware stores like Home Depot or Lowes are 26-gauge galvanized steel ducts.
90-degree elbows, round trunk lines, and even Plenums are typically composed of 26-gauge galvanized steel. Things like distribution lines and other parts can be easily acquired, but if you are interested in aluminum, the options are fairly limited from traditional big-box hardware stores.
Locating pricing on rectangular ductwork was challenging considering it’s not as frequently used, but the table below will give you a rough idea of what to expect. It includes short runs of ductwork between 2’ to 6’ in length along with standard parts like elbow and clamps. Most of these products can be found locally through Home Depot or Lowes
Round Duct Pipe
4” x 2’
Round Duct Pipe
4” x 2’
Heating & Cooling Products
18” x 5’
4” x 4”
Heating & Cooling Products
Stack Duct (Half)
10” x 5’
Heating & Cooling Products
8” x 10” x 4’
Oval Duct Pipe
6” x 5’
Ductwork Installation Cost
Installing or replacing sections of existing ductwork in your home isn’t as expensive as having an entirely new HVAC system installed. That said, it can get pricey depending on the material used and labor along with the style and size of your home.
The main thing to keep in mind when dealing with ductwork is leaks and efficiency. If you simply have a short 3’ to 4’ run that needs to be replaced, it’s something you can probably tackle yourself unless it’s in a tricky location. You don’t need a wealth of tools but may get a little dirty depending on where the air ducts are located in your home or have to deal with cramped locations.
If it’s a major overhaul of your HVAC systems ductwork, you may want to consider a professional for a variety of reasons. Ductwork needs to be the right size and designed with a balance between the airflow return and supply. It needs to be the right thickness as well so it can handle the pressure, but light enough to not cause issues and hung to prevent sagging or leaks.
A leak can lead to dirty air vents and mold along with the decreased efficiency of your system. If you’re interested in hiring a professional to replace ductwork in your home, use our quote tool to find certified HVAC professionals in your area.
Whether you are considering low-profile ductwork in a tight crawl space or are trying to plan ahead before calling a contractor, knowing what’s available from ductwork manufacturers can give you a significant advantage. If you’re interested in learning more about ductwork and the process behind the installation, this guide will walk you through the fine points.
Q: How can I shut off air to a certain section of my home during the summer or winter?
A: While closing the vents always helps, the only foolproof way to redirect airflow or shut off an upstairs area from an HVAC system is to use a damper.
Q: When should I have my ductwork cleaned?
A: The NADCA recommends having your air ducts cleaned once every 3-5 years. If you live in a dusty region or have bad ductwork, it may need to be cleaned more frequently.
Q: What’s the best way to seal a leaky metal air duct?
A: Mastic cement and aluminum HVAC tape are both used by professionals to repair ductwork.
Q: How much does it cost to clean air ducts?
A: That depends on the size of your home and its location. In our research, we found the average price to be between $400-$1000 in most cases.
Q: Is it possible to have a central system without running ductwork?
A: No, but you can consider a high-efficiency HVAC system in the mini-split class depending on the size of your home.
Q: Should ductwork be insulated?
A: Wrapping metal ductwork with insulation has a variety of benefits and can help to regulate the temperature in the vents while reducing the chance for condensation.