Metal Ductwork vs Flexible Ductwork

South End Plumbing, Heating, & Air Expert Tips

Metal Ductwork vs Flexible Ductwork

Metal Ductwork vs Flexible Ductwork

HVAC contractors have actually stopped utilizing metal ductwork as their default duct product ever since the 1980s. The default ducts you’ll see in houses now are flex-type ductwork, however, that does not indicate that it’s better for airflow. This post will compare metal ductwork vs flexible ductwork and assist you in choosing which is much better for your home.


Sheet Metal Air Ducts

Sheet metal ductwork can be found in two types, rectangular sheet metal and round ductwork. Rectangular sheet metal can be found in 3-4′ sections and is held together with S cleats and drives. Ranch-style houses that have registered above the bedroom entrances and a dropped 8′ ceiling in the corridor have this type of ductwork.

The rectangle-shaped sheet metal ducts are nailed into the framing of the home and are difficult to take out without removing the ceiling. Houses integrated in the 1970s-80s have this ductwork type providing the conditioned air from a central heating & cooling system but likewise from an evaporative cooler.

Rectangular Ductwork

Rectangular sheet metal ductwork is excellent for airflow since the ducts are oversized to accommodate the big quantity of air provided by the AC. Research studies have actually revealed that metal ductwork is not always much better than flexible ductwork but the benefit of metal ductwork is that is difficult to set up wrong. Metal ductwork does not kink as quickly as its flexible ductwork equivalent. As I’ll go over later, flexible ductwork is not just simple to install, it’s likewise simple to set up wrong with kinks over trusses or electrical wires, too much length, or tough 90-degree flexes

Round Metal Ductwork

The second kind of metal ductwork is round stiff metal ductwork. Round metal ductwork can either be spiral duct, which comes in one 10′ section of different sizes and is not insulated. This is an excellent solution for restaurants, business buildings, and even houses that want a commercial look. Insulating spiral ductwork more than doubles the price due to the fact that the insulation is cut and glued in between each of the spiral ribs. For this reason, uninsulated spiral ductwork is primarily utilized in conditioned areas. The second kind of round stiff ductwork is KD pipe which is snapped together at the seams and comes in 3′, 4′, or 5′ areas depending upon the size. This ductwork likewise comes uninsulated and can quickly come apart if not mechanically fastened together and can be deformed and squashed if walked on (yes, I have seen cable television guys, HVAC service technicians, insulation installers, and electrical experts all crushed this kind of ductwork and left as a causality of their work). The airflow is a little better in KD pipe than in compressed flexible ductwork, however, if the flexible ductwork is pulled securely the airflow will be the same.

The Downsides of Metal Ductwork

The drawbacks of metal ductwork are that it rusts and it leaks. With new homes the rust isn’t much of a concern however with homes that likewise had a swamp cooler installed with metal ductwork, there’s a high chance of rusting currently taking place in the metal ductwork. Rectangle-shaped metal can rust so badly that it rusts all the way through.

Because metal ductwork is only available in 3-foot sections (compared to a 25-foot bag of flex ducts), there are plenty of joints and locations where air can escape. In addition, if the metal ductwork was never ever sealed before the drywall was installed when the house was being constructed, the bottom half of the ductwork becomes unattainable to seal by hand and needs a more expensive Aerosol procedure to seal effectively.


Flexible Ductwork

The alternative to metal ductwork and the most frequently utilized type of ductwork today is flexible ductwork. Flexible ductwork is made from 3 different sections, an outer reflective sleeve, an insulation layer, and a vinyl plastic inner liner with a metal spiral rib holding its shape. Flexible ductwork was first used in homes in the 1980s with a clear inner liner. This type of ductwork has been outlawed as it degrades and becomes so breakable it will split and split open with the air pressure. When changing your air filters, if you see a clear inner liner at the return duct, you know you have this kind of ductwork.

Flexible ductwork needs to be installed properly to get the correct amount of airflow to each space and a bad setup can significantly impact airflow and convenience in your home. This implies no kinks, using 90-degree elbows at all ceiling cans and the ductwork is pulled tight with minimal slack to minimize friction resistance.

Can Metal Ductwork Be Retro Installed?

Yes, it is possible to swap out the flex ductwork in your home for all metal ductwork but it is pricey. Metal duct installers use to have a name, tin-knockers, because of the skill needed to measure, produce and install the ductwork was a skill. Today, there is no name for those that set up flexible ductwork. The fact is anybody can set up versatile ductwork, so anybody and everybody do it. With little to no training, installation’s finest practices head out the window, which is one of the primary reasons it’s risky to get a bad installer.

Setting up metal ductwork in an existing home is pricey for 2 factors.

1. Material Costs are on the Rise
Buying the metal today is costly, and it’s still on the rise. Currently, the costs of the ductwork can be as much as 3 times as much as flex ductwork.

2. Labor is Expensive
Because of the limited attic access, a 10′ area of ductwork can be impossible to move to where it needs to go. Simpler attics to get around have greater pitches and a lot of space to walk around but even then, it’s most likely a two-guy task to just set the ductwork in place. When set, the ducts need to be protected, sealed, and after that covered in insulation. The right elbows and bends need to be in place to terminate the ducts into the ceiling cans and signs up and all that labor can build up quickly. It can be done however you need to ask yourself if a little improvement in airflow with metal ductwork deserves double the expense of installation versus decently install versatile ductwork.

Can You Get Metal Ductwork On A New Home?

What about installing metal ductwork on a new construction home? Metal ductwork can be better for airflow and the installers don’t have to deal with the area limitations that come with existing homes, so it would make sense that the cost drops. Well, not always since insulated metal ductwork can be two times or more the cost of versatile ductwork. If you want to pay double the costs of flexible ductwork and have the peace of mind that all the airflow coming out of your unit is entering your house then metal ductwork is the way to go on a recently constructed house.

Kinked Flexible Ductwork
Kinked Flexible Ductwork

The Downside of Flexible Ductwork?

Nothing is wrong with flexible ductwork when installed properly. It is on par with sheet metal ductwork for airflow. What’s wrong with flexible ductwork is that it’s too easy to set up incorrectly. What could go wrong with flexible ductwork installation? Here is a short list.

  1. Reduced Airflow (Compression) with additional lengths
  2. Reduced Airflow with hard turns
  3. Improper fittings
  4. Double support from poor planning
  5. Wrong sizes required to fit

These issues can undermine your airflow and HVAC performance. With all the ways to set up flex duct incorrectly, you would think that installing it properly is quite basic. You simply pull the ducts tight and hook them up. It’s in fact harder to set up flexible ductwork correctly than you would believe. On one hand, we desire a tight pull on the ductwork, but too tight a pull will disconnect the duct from one end or rip the duct if it’s mechanically fastened by a zip tie. Flex duct that’s pulled too firmly produces tight bends at the terminals aka ceiling cans and laying over trusses. A 90-degree elbow is needed at the ceiling cans for optimum airflow going into your home. That way the ductwork can be pulled tight and still make a 90-degree bend going into the house. Lots of HVAC professionals like to strap the ductwork up along the roofing trusses to assist ease the drop down into the ceiling terminals, nevertheless, this leaves the ductwork exposed to the hot attic air. We like to drop the ductwork when possible, install 90-degree elbows at the terminals, and bury the duct in insulation.

The Upsides of Flexible Ductwork

There are good attributes to flexible ducts that outweigh the bad.

Versatile ductwork is less expensive than metal ductwork. By the time you include insulation onto the expense of metal ductwork, you are practically double the expense of flexible ductwork that comes pre-insulated (purchase the R8 insulated ductwork versus the R6).
Flexible ductwork is quicker to set up than metal ductwork. Even with the additional time installing 90-degree elbows, trimming the ducts to the right length, properly sealing and running the ductwork most efficiently, it is fewer man-hours and more expensive than covering 3-10 foot lengths of sheet metal ductwork, securing them together, sealing the metal joints and finally wrapping whatever in insulation.


If flexible ductwork is installed correctly, the airflow will be the same or better than metal ductwork. It’s all in the installation. The benefit of metal ductwork is that you are taking less of an opportunity for the ductwork to be set up wrong than with versatile ductwork. It’s harder to install metal ductwork incorrectly than it is flexible ductwork. If you can discover an installer that follows the best flexible ductwork installation, then there’s no distinction between airflow from flex ductwork compared to metal ductwork. The expense will be considerably less with flexible ductwork compared to sheet metal ductwork.

At South End Heating & Air we specialize in Furnace Repair and Replacement, contact us for a free consult. We’ll evaluate your system and help make recommendations for optimum value. After all, we want to keep you cool all summer long and warm in the winter. Just schedule a visit with one of our technicians to talk about how we can help with your thermostat settings. Would you like to learn more options our techs can help you with? give us a call at 704-684-5339

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