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Can Fiberglass Insulation Touch Ductwork? Key Considerations

Can Fiberglass Insulation Touch Ductwork? Key Considerations

Fiberglass is one of the most common household insulation methods. It’s easy to use, long-lasting, and budget-friendly. There are a few drawbacks to using fiberglass insulation, but all of them can be limited or completely prevented by following the proper installation procedures.

Fiberglass insulation can touch HVAC ductwork provided the ducts are not leaking or forming too much condensation. The insulation should be snug enough to prevent significant gaps throughout the ductwork.

Throughout this article, you’ll also learn the following details about fiberglass insulation and ductwork:

  • How to properly install fiberglass batts around your ductwork
  • Various areas of concern that you might run into
  • The pros and cons of hiring a professional for the insulation process

Note: This article focuses on insulation near ductwork for HVAC. We also have guidelines on insulating around furnace exhaust vents.

How to Use Fiberglass Insulation Around Ductwork

If you want to use fiberglass insulation, you’ll want to use specially-designed foil-backed insulation wrap (link to Amazon). Measure out how much you’ll need before ordering.

Here’s how to do it:

  1. Clean the ductwork if it’s dirty, and inspect it for leaks. Leaks can cause all sorts of issues, which will be discussed in the next section. Once you’ve noticed that there aren’t any issues with the ducts, you’ll start cutting the fiberglass insulation.
  2. Using a sharpened knife, slowly slice the foam batts linearly. As This Old House mentions, you can also attach foil tape to the batts if it doesn’t already have a built-in adhesive.

    You can find foil tape for a low cost, such as the Foil Duct Tape (link to Amazon). These tapes are temperature-resistant and for the most part perfectly fine to use.

    Although tape has it’s advantages, I’m fond of using a true duct sealant like Red Devil (Link to Amazon). It’s a little more work to apply (it’s like a putty) but you get a seal that isn’t going to peel away like tape.
  3. Lay the fiberglass strips on the ductwork longways. Apply firm pressure as you lay down each section, ensuring that there aren’t any gaps between strips. Pinch them together to prevent gaps, then consider adding another layer of foil tape to seal the connecting portions.
  4. Ensure that you can still separate and repair the ductwork if needed. You can do this by measuring and marking the spots that have connection pieces. Wherever they lie, you can omit the taping suggestion. This will allow you to repair the ductwork as needed.
  5. Inspect the fiberglass insulation to ensure that it’s not puffed or loosened. Fiberglass is one of the best insulators in the world, but loosened fiberglass can cause respiratory issues. You’ll need to be careful to prevent such issues from occurring.

As you can see, installing fiberglass insulation on your HVAC ductwork is easy. There are a few stipulations, though, all of which will be listed in the next section.

Possible Risks Associated With Ductwork and Fiberglass

Nothing in the world of HVAC is risk-free. The good news is that you can have it safely installed by a professional. If you’re worried about what might happen when ductwork touches fiberglass, you’re in the right place.

Here’s a list of possible risks that might occur if ductwork touches fiberglass insulation:

  • If there are leaks along the ductwork, condensation can buildup. Condensation and other sources of moisture cause mold and mildew to grow on fiberglass insulation. It’s a health hazard that can also wreak havoc on the insulation and ductwork.
  • As mentioned above, loose fiberglass batts can cause breathing issues. Fiberglass batts are designed to stay compacted throughout the installation process, but that doesn’t prevent sloppy work from ruining them.
  • If the ductwork is porous or cracked, it could pull fiberglass fibers through. This problem would result in small shards of fiberglass spread throughout your home, which has obvious negative side effects. Although it’s incredibly rare, nothing beats a good old fashioned inspection.

So, above all else, your first step is ensuring that the ductwork is air-sealed.

As an FYI – According to the Engineering Toolbox, fiberglass has a heat threshold that’s well over 500°F or 260°C.

Should You Hire a Professional for Installation?

Fiberglass insulation can be installed around ductwork by a professional if you are not comfortable with the process yourself.

Hiring a professional is often the first thing that most people do when dealing with issues like this. However, for those of you who are self-described DIYers, you might be on the fence about paying extra money for someone else to do it.

I tend to do projects like this myself but here’s the deal. This is much easier to do prior to the ductwork being installed. If it is already in place, you very well may need a professional. It’s going to depend on how accessible the ductwork is and your physical ability. I could do a lot more of this 20 years ago than I can now.

Below, we’ll examine the pros and cons of both sides of the equation.

Pros of Hiring an Expert

  • If anything goes wrong with the job, you’ll be able to point the finger at the company. You don’t have to take the bill for a botched job if you have written proof. Furthermore, it’ll give you leverage for a potential warranty from your home insurance policy provider.
  • You don’t have to worry about getting everything at the store by yourself. It always seems like DIY jobs are missing one small yet crucial piece of the puzzle. Hiring an expert will ensure that you can relax in your own home while they do all of the work.
  • Many companies provide long-term insulation warranties. If anything goes wrong, they’ll come back and fix it according to their terms of service. Always ask about potential warranties prior to agreeing to anything.

Cons of Hiring an Expert

  • You know your home better than anyone else. They might have the knowledge, but you’ll have to communicate all of the intricate details about potential leaks and other possible concerns.
  • It always costs more to hire a professional to do HVAC work. They charge quite a bit, so you’ll be left with a bigger hole in your pocket at the end of the process.

Pros of DIY Insulation

  • If anything goes wrong, you’ll know right where the problem stemmed. Jump on it and fix the issue in minutes rather than wait for another company to come out on their time frame.
  • Perhaps the most obvious advantage of doing it yourself is that you’ll save loads of money. You can choose the most cost-effective materials, get it done on your own watch, and avoid labor, service, and trip charges.
  • This job is simple, but it’s enough to boost your confidence in other HVAC work areas. Who knows? You might save hundreds or thousands of dollars down the road from doing DIY projects on the ductwork.

Cons of DIY Insulation

  • The only severe issue that you might encounter when doing it yourself is doing it wrong. You’ll void all warranties, spending more money out of your paycheck than you would’ve if you’d just hired a professional to come out and do it for you.


Under ideal operating circumstances, fiberglass insulation can touch ductwork without a problem. In fact, it’s often intentionally applied right against the surface by hundreds of professionals throughout the year.

You should make sure that there aren’t any leaks, holes, or weakened parts of the ductwork before you get started. If you’re still concerned, hire someone to inspect the ducts to give you peace of mind.

Here is a quick rundown of the post:

  • Fiberglass batts should be cut linearly, then installed along the surface of ductwork in long strips.
  • Condensation from leaky ducts can create mold and mildew in fiberglass.
  • Fiberglass can be heated to over 500°F (260°C) before it starts to overheat.

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