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How to Insulate Ductwork in Garage: The Perfect Guide

Uninsulated ductwork can be a barrier to getting your cozy home. It funks up your garage’s temperature balance. And let’s not forget about the humongous bill you’re slapped with.

Naturally, the question arises, how to insulate ductwork in garage?

Before going for insulation, you’ve got to get your tools. Now, put some thought into choosing the insulating material as well. After picking the material, you need to mend the pre-existing leaks. Then cut the insulation, place it properly and ensure it stays that way.

That was just the surface of the solution. So, to get to the main event, keep on reading and thank me later.

Let’s put those handyman overalls on and get to it.  

Grab All the Tools

Ductwork doesn’t need much equipment. But before that, you have to know which tools. Once you grab those, you are good to go.

Getting The Right Safety Gear

In any case, safety comes first. So, don’t forget to get your protective gear on, before rushing to work. You’ll need:

  • Protective Clothes
  • Goggles
  • Dust Mask
  • Gloves

Tip: Work can get a bit tricky with heavy gloves. So, it’s better to wear rubber gloves.

Selecting Insulation Material

There are many options for insulation products. So, it’s very important to pick the right insulation according to your use.

Insulation Type

Among the many types, rigid, batt, blow-in are some fine examples of insulation. Now, different areas and weather demand different care. So, your house may have specific needs due to extreme weather. Either, that is hot or cold weather and their insulation.

Are you planning to cover ductwork in your garage? You’ll need something flexible with great support. So, it’s best for you to use fiberglass insulation. 

Determining R-Value

Evaluating the R-type is very important for insulation to work right. R-value indicates the resistance value of the insulation. So, the higher the value, the less likely heat will penetrate.

R-value can vary depending on the climate and different areas of the home. 

It’s best to use insulation with R-6 or higher R-value for covering garage ductwork. 

Step-By-Step Insulation Process

Keeping your garage well maintained can give you extra storage for many things. But it’s not easy. You have to keep it clean, level the garage slope, and now insulate ductwork. 

Insulation saves energy and keeps your home temperature in check. And let’s not forget, it gives your air-conditioner a bit of peace.  

They need a little place to breathe with all the air conditioning they do. Well, even if this pun doesn’t hit the spot for you, the easy guide to insulate your duct will. 

Here go the steps:

Repairing Leaks in Ductwork 

The whole insulation process will be pointless if there are leaks in the ducts. Even after the insulation, the air leak will harm the air conditioner.

Let’s go step by step to cover all bases:

Step 1: Finding the Leak

Detecting leaks is a piece of cake. 

Firstly, turn on your HVAC system. Then, try to feel along the ducts for any kind of leakage. You should focus on the joints and rusty areas. 

Smaller leaks are hard to detect. So, mark the leak immediately, as soon as you find them. Then turn off the system. 

Step 2: Picking the Right Sealant

Sealant preference varies due to product material and resistance. Both foil and mastic tape works great in this case. And if the leak is too big, you can always use liquid mastic with a brush. 

No matter how small the leak is, don’t use duct tape. They tend to give away pretty easily in extreme heat.  

Here are some of our favorite sealants we prefer using:

Recommended Products



Don’t forget to clean the ducts before you start sealing as well. Because dust can weaken the sealant’s bond.   

Step 3: Covering the Leak

Now that you have picked the sealant, let’s start sealing. Cover all the leaks with the tape and put an extra layer of taping on the joints. Even if there are no leaks. Being generous with layers will ensure no leaking in the future.  

You can even use your hands or a brush to secure the tape.  

Insulating Ductwork

After covering all the leaks, it’s time to attach the insulation. Remember the procedure is almost similar to insulating your basement or attic. So, let’s get to it.

Step 1: Cutting the Insulation 

Finally, it’s time to cut that insulation and place them right. To do so, use a sharp utility knife. And make the piece a little larger than the duct in size. You might need to run ductwork perpendicular to joists.

This is so it can overlap the seams. So, there’ll be no place for exposure. 

Step 2: Checking the Right Placement Of Insulation

In all haste, don’t forget to check whether the insulation is facing the right way. You don’t want to finish and then find out the placement is all wrong. 

Make sure the fiberglass side is on the ducts. Also, check that the vapor barrier is on the outside.

Step 3: Covering Insulation with Tape

Let’s start wrapping that insulation now. Firstly, place several small tapes along the seams to cover it entirely. And then, use a large tape to cover from top to bottom. 

Don’t forget to apply the same procedure in between the pieces. 

You can even do this for your already insulated ducts. If the previous insulation is in good shape, you can just add another layer over it. Otherwise, remove the previous layer to work on it. 

Follow the same steps even after moving your garage. And you’re good to go!

Tip: Don’t press the insulation too tight. The R-value of the insulation depends on the air space inside the fiber. And, it may drop a few levels if the air space is compromised.


Question: Is insulating ductwork worth it?
Answer: Ducts are used for HVAC systems. And, exposed ducts result in the air conditioner working twice as hard. Which leads to huge utility bills. So, it’s very cost-efficient to insulate ducts in unconditioned space.

Question: Can you use Flex Seal on ductwork?
Answer: Flex Seal can be used on ductwork or interior HVAC walls. However, if you use vinyl ductwork, remember, Flex Seal isn’t compatible with vinyl. 

Question: What kind of tape is used for ductwork?
Answer: Foil tape is the best option for ductwork. It can withstand both hot and cold temperatures. That too without drying out or shrinking. Mastic tape is also a good option. 


We’ve answered all your questions on how to insulate ductwork in garage. Now, go fix your garage ducts and enjoy the cozy weather in your house. 

Did you find any additional tricks to make the process easy?

If you haven’t, all the best with your project. Don’t forget the safety measures!