If you need to install ductwork, you’ll likely need to choose between flexible and metal ductwork for the job. But this can be tough to do if you’re not sure about the pros and cons of each option.
The main difference between flexible and metal ductwork is that metal ductwork is rigid, while flexible ductwork can be manipulated. Flexible ductwork is typically the cheaper and quieter option. But metal ductwork provides superior airflow and is more durable.
But there’s more that you need to know about these two types of ductwork before you can make a decision. That’s why we’ve put together this article. Keep reading to learn everything that you need to know about flexible vs. metal ductwork.
An overview of flexible vs. metal ductwork
Both flexible and metal ductwork are viable options for your next project. The one that’s best for you will depend on factors like:
- Where you’re installing the ductwork
- Your budget
- What type of airflow you need
- Whether you value flexibility or durability more
For example, metal ductwork is often the better choice when it’s going to be exposed. But flexible ductwork works great in tight crawl spaces.
Reading through the sections below will give you the information you need to decide which of these is right for you.
Installation
Flex ductwork is lightweight and bendable. This means that it’s usually much easier to install than metal ductwork. So if you’re just looking for the easier installation option, then flexible ductwork is the way to go.
Sheet metal is more challenging to install for a few reasons. First, it’s heavier than flexible ductwork. This can make it a pain to drag around and position.
Additionally, metal ductwork doesn’t have any bend in it. So it can be pretty challenging to get it into the right position. You have to be really accurate with the sizes you choose as well.
That being said, flexible ductwork is also easier to mess up during installation than metal ductwork is. It gets kinked rather easily. When that happens, it compresses and reduces the amount of airflow that the ductwork has.
Flexible ductwork is also rather prone to being punctured since it’s soft. That means the installers need to be careful with it or else risk ruining the effectiveness of the HVAC system.
☆ Winner: Flexible ductwork
Is flexible or metal ductwork cheaper?
Flexible ductwork is cheaper than metal ductwork by about 50%. That’s true for a few reasons.
First, the material that makes flexible ductwork is cheaper to produce. Additionally, flexible ductwork comes pre-insulated, while metal ductwork does not.
On top of that, you should expect to pay more to have metal ductwork installed. That’s because it takes time to seal all of the seams, joints, and elbows that it has.
Flexible ductwork doesn’t have this problem. There’s no need to seal any seams since it doesn’t have any. So both your installation and material costs should be cheaper if you go with flexible ductwork.
☆ Winner: Flexible ductwork
Design
Both flexible and metal ductwork have roles to play in different parts of an HVAC system. The option that’s best for your project will depend on the design needs of that part of your system.
For example, flexible ducts are better if you’re branching off the main plenum of your system. They’re really effective at carrying air to ceiling vents in each room.
Flexible ducts are good in this role because they’re available in many materials. You can get them in:
- Rubber
- Stainless steel
- Silicone
- Polyurethane
This makes it easy to find the specific material that’s going to work best for your project.
Metal ductwork works better as the major portion of a trunk-and-branch layout. For example, if you need to connect directly to a furnace, metal ductwork is likely the way to go.
Another thing that’s worth mentioning is that flex ducts are typically quieter than metal ducts. This is because air can whistle while moving around metal ductwork. But that doesn’t happen with flex ducts.
☆ Winner: It’s a tie. Both have their purpose in different parts of an HVAC system design.
What type of air resistance do flexible and metal ductwork offer?
Air resistance is another factor you need to think about while making this decision. If a material causes too much of this, it will diminish the effectiveness of your HVAC system. When you minimize air resistance, you maximize the strength of your HVAC.
Flexible ductwork has more air resistance than metal ductwork. It tends to crumple up and restrict airflow because of its flexible nature. Inexperienced contractors may install flexible ductwork in ways that make this happen more often than it should.
Metal air ducts don’t have this problem since they aren’t flexible. But they do have their own air supply issues.
Metal ducts are mostly about three feet long. That means there’s a seam every three feet where two pieces connect. Seams also exist where metal ductwork turns.
These seams can cause air leaks. While this is a different problem than air resistance, the impact is largely the same. That being said, you can avoid this becoming a problem by simply ensuring that seams are closed tightly during installation.
☆ Winner: Metal ductwork
Durability
Metal ductwork is generally considered to be more durable than flexible ductwork. This is the case for a few different reasons.
First, metal ductwork is built out of sheet metal. This material essentially can’t be punctured.
Flexible ductwork, on the other hand, typically features an inner polymer tube and an outer foil jacket. Both of these materials are very easy to puncture.
That’s why most experts say that metal ductwork typically lasts longer than flexible ductwork. The only reason that wouldn’t be true is if the metal ductwork is installed in a rust-producing environment.
Flex ductwork is also really difficult to clean. Its insides are made out of a thin polymer substance. And you need special tools to clean this without puncturing or breaking it. That’s not a problem with metal ductwork.
☆ Winner: Metal ductwork
When is metal ductwork the better option?
Metal ductwork will be a better choice for your project if you’re looking for the specific benefits that it offers. This type of ductwork is:
- Highly durable
- Easy to keep clean
- Long-lasting
- Available in many sizes and with many fittings
Features like these add up to mean that, if you buy metal ductwork, it should last you a long time. So if you want durable, long-lasting, effective ductwork, metal ductwork is the way to go.
When is flexible ductwork the right choice?
There are a number of scenarios in which flexible ductwork may be a better option for you than metal ductwork. We’ll quickly review each of those scenarios in this section.
You’re on a budget
Flexible ductwork is usually much less expensive than metal ductwork. In some cases, you may be able to reduce the costs of your project by as much as 70% by choosing it.
That’s because both the flexible ductwork material and installation costs are cheaper than metal ductwork.
You’re going for a DIY installation
Flex ductwork is also typically better for homeowners who are doing a DIY installation. That’s just because flexible ductwork is easier to handle than metal ductwork.
Additionally, the installation process takes fewer and less-expensive tools to complete. That’s because you won’t have to worry about cutting and connecting pieces of sheet metal.
You already have flexible ductwork
It’s also typically easier to add the same material that your HVAC system already uses. So if yours is already built out of flexible ductwork, you should probably continue using it. Otherwise, you could increase your costs by trying to connect flexible ductwork to metal ductwork.
You’re installing the ductwork in hard-to-reach areas
One of the main benefits of flexible ducts is their versatility. You can bend them around various parts of your home, like roof rafters, with ease.
The same isn’t true of metal ductwork. It can be really tough to install in hard-to-reach areas because it’s heavy, bulky, and doesn’t flex at all.
So if you need to install ductwork in an area that’s tight or tough to reach, flexible ductwork makes more sense.
Flexible ductwork and airflow restriction
Many people worry about using flexible ductwork because of the airflow restrictions that it can have. This is certainly a valid concern and one that you should keep in mind while making your decision.
Flexible ductwork causes a small amount of interior air turbulence because of its coiled-wire design. This means it doesn’t allow as much air as metal ductwork does.
For example, a round 10-inch metal duct lets about 325 CFM through it. But a flex duct of the same size allows about 300 CFM through it. So you’re missing out on about 8% of potential airflow.
But really, it all comes down to your installation. If flexible ductwork is installed correctly, it can match metal ductwork in terms of air resistance.
The question is, how confident are you that your ductwork will be installed optimally? If you’re not very confident, then metal ductwork will be a safer option for your project.
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