How to Cut Flexible Ducting in 6 Easy Steps

Keep your ductwork skinny jeans tight

Worker installing flexible aluminum
Photo: ronstik / iStock / Getty Images Plus / Getty Images
Worker installing flexible aluminum
Photo: ronstik / iStock / Getty Images Plus / Getty Images
Deirdre Sullivan
Written by Deirdre Sullivan
Contributing Writer
Updated Mar 11, 2025
SKILL LEVEL
Intermediate
COMPLETION TIME
1 hour
COST
$100–$500
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What you'll need:
TOOLS
  • Long knife or hacksaw
  • Tin snips
  • Protective gloves
  • Safety goggles
SUPPLIES
  • Rubber band
  • Permanent marker
  • File

Your ductwork is like the veins of your home, carrying air from your HVAC system through its air vents. As such, having ductwork that fits well can prevent many problems from arising, like condensation in air vents or air leaks that could spike your energy bills. That’s why, if you’re working with flexible ducting, you want to ensure it fits well. Our guide will walk you through how to cut flexible ducting and address common problems that arise with ductwork. 

Prepping to Cut Flexible Ducting

You want to have a dedicated work space to do your cutting. If you have a workbench, it’ll be the perfect area to collect your tools and make your cuts. Further, if you’re a newbie tackling this project for the first time, it’s ideal to have someone you know who’s done this project before, or you could hire a handyman to work together. That way, you learn as you go, and they can help you ensure everything fits according to your HVAC system’s design. 

How to Cut Flexible Ducting

Now that you have your supplies organized and a dedicated space to do the work, here is a step-by-step guide on how to cut flexible ducting:

  1. Put on Safety Equipment

    Man wearing safety gloves
    Photo: Tomasz Zajda / Adobe Stock

    Start by putting on your safety glasses and work gloves. This will protect your eyes from flying debris and keep your hands safe while you work with the ductwork. Also, make sure your work area is clear aside from the tools and materials you need to finish the job. Doing this makes it easier to move around and you don’t have stuff in the way while you make your cuts. 

  2. Secure the Ductwork

    Take a rubber band and wrap the ductwork where you want to cut it. Keep the fit slightly wide, as this allows you the chance to smooth over any rough edges after finishing the cut. 

  3. Mark Your Cut

    Flexible aluminum air ducting
    Photo: Image by Marie LaFauci / Moment / Getty Images

    Use a permanent marker to mark the line you’ll cut. This can help guide you to ensure it’s as smooth and as straight as possible. 

  4. Cut the Ducting

    Take your hacksaw or long knife and cut the flexible ducting. Make sure to have your plant hand, the one holding the ductwork, away from your cutting hand at all times. Also, make sure to cut away from your body, as this can protect you from incurring injury. 

  5. Snip to Complete the Cut

    Towards the end of the cut, you can use a pair of tin snips to complete it. This ensures the cut is as smooth as can be, making it a better fit for your C-box, which is where you connect the ductwork. 

  6. Smooth Rough Edges

    Man trying to change an old aluminum foil
    Photo: Boyloso / iStock / Getty Images Plus / Getty Images

    After completing the cut, examine the edges of the ductwork. Feel for any rough edges, and upon finding them, smooth them using a file.

How to Solve Common Ductwork Problems by Cutting Flexible Ductwork

One of the reasons why you might cut flexible ductwork is when you notice a problem with it. Here are some signs that your ductwork could need work:

  • Condensation: Condensation happens when warmer, outside air combines with the cool air traveling through your ductwork. If you want to learn how to stop condensation on air vents, doing a DIY dry leakage test is a smart option to take. With this approach, you’ll run your hand over the ductwork while your HVAC is on. If you can feel air blowing out, it indicates a leak. 

  • Dirty ducts: When you don’t properly maintain ductwork, it can lead to particle buildup. From here, it blows that dirty air through your air vents into your lungs. That’s why, once every five years, you’ll need to do a duct cleaning. The average air duct cleaning costs $380. 

  • Outdated: Ductwork lasts on average 10 to 15 years with the proper care. If you’re approaching the end of its operational life, it’s a wise choice to replace them. Your local installer can go over options, answering questions like what is the most efficient ductwork? While this is a significant expense upfront, you’ll also be breathing cleaner air, helping your HVAC operate more efficiently, and potentially seeing lower energy bills. 

How Much Does Professional Ductwork Repair Cost?

The cost of repairing your home’s ductwork depends on several factors. The type of repair needed, the materials used in your duct system, the location of the issue, and how easily technicians can access it all affect the final price. 

On average, homeowners spend about $660 on duct repair, with the typical range being $200 to $2,100. Issues like leaks, rust, and mold remediation can raise out-of-pocket costs.

DIY vs. Hiring a Pro

Depending on your experience level, going the DIY route suits minor issues like sealing small leaks. But remember that improper repairs can lead to energy loss and poor air quality.

Hiring an experienced duct installer near you is always the best idea for extensive damage, hidden leaks, or duct replacement. It is the most efficient way to ensure proper sealing, insulation, and airflow. Yes, it is more expensive up front, but expert repairs improve HVAC performance and reduce long-term energy costs, which is a win-win.

Frequently Asked Questions

The best tool for cutting ductwork depends on the material. Aviation snips or electric shears work well for sheet metal ducts. A reciprocating saw or angle grinder handles thicker sections. A utility knife and wire cutters are ideal for flexible ducting.

Flexible ductwork offers many advantages, as it’s easy to install and it’s less expensive than other types of ductwork. On top of this, it’s flexible. This means it’s better suited if you have a home with some curves, tight crevices, and corners. You can work with your local duct installer to find solutions that fit well with your home’s design. 

You can do simple maintenance to keep it clean and operating in peak condition. Start by replacing the furnace air filters as directed–often, this is once every month or every three. Next, clean your air vents once a month, as they can help you see how much dirty air filters through. If you notice them becoming dirtier, you should have your ducts cleaned. With flexible ducting being more susceptible to tears, you’ll want to hire a pro to do the work for you. 

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Learn more about our contributor
Deirdre Sullivan
Written by Deirdre Sullivan
Contributing Writer
Deirdre is a seasoned DIYer and home improvement writer. She believes in the transformative powers of deep cleaning and painting to revitalize any space. Her articles have appeared in HomeLight, The Spruce, Realtor, and more.

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