How to Insulate Ductwork in Basement or Attic (With Steps)

How to Insulate the Ductwork in a Basement or Attic 

Exposed ductwork is energy inefficient, especially if it also has air leaks. You’re wasting up to 30% of the heated or cooled air with exposed, poorly sealed ducts. With that in mind, insulating the existing ductwork in your basement/crawlspace or attic is something that every homeowner should strongly consider doing.  You will recoup the cost of ductwork insulation in a few years through lower energy bills, and your HVAC equipment will last longer because it doesn’t have to work as hard. Ductwork insulation has a great return on investment!

What You’ll Read Below

We start with the importance of insulating ducts, but you’re probably already in agreement there, since you’re reading this Pick HVAC page.

The step-by-step process of how to insulate ductwork in your attic or basement will be shared in detail.  The materials needed and how to use them will also be listed and explained.  If you have uninsulated ductwork, this is the place to go for all your needed information and education.   

Why Should You Insulate Your Ductwork? 

We mentioned energy efficiency by reducing energy loss through uninsulated ductwork when heating and air conditioning your home. Ecofriendliness shouldn’t be overlooked. The more energy that is conserved or saved, the better it is for the environment.

Plus, the fact your equipment won’t work as hard to keep your home comfortable.

It’s also true that if your HVAC system is properly sized but you’re losing a lot of the treated air with uninsulated and possibly leaky ductwork, your furnace, heat pump or AC might not be able to keep up, and parts of your home won’t be adequately heated or cooled.

OK, we’re all on the same page now. Let’s talk about how to insulate ductwork in the basement or attic. 

Duct Insulation Options 

It starts with material. When you decide to insulate your ductwork, you have a few options available to choose from. Cost-effective options that are best suited for insulating the ductwork in your basement, crawlspace or attic will be constructed mainly of fiberglass.  First of all, you can choose between either flexible or rigid insulation.  The types available for HVAC insulation are duct liner, duct wrap and duct board.  Each of these options can be purchased separately and with a variety of R-factors.  R-factor is defined as the resistance to heat loss in insulation. The higher the R-factor, the better the insulation will be to limit heat loss.

Pro Tip: Spray foam insulation can also be used on exposed ductwork. The cost per square foot is higher when a pro does the job, but so is the insulation value (R-value). DIY spray foam kits are available if you want to save money. Just be sure you meticulously follow the directions for maximum benefit. Most brands like Dow and Touch N’ Seal have DIY tutorials, and we recommend watching them before insulating basement / attic ductwork.

You can compare the cost and R-values of spray foam vs fiberglass insulation on this page.

Insulating Ductwork – What Tools/Materials are Needed 

The following tools and materials are needed in order to install ductwork insulation in your basement, attic, and/or crawl space:

  1. Goggles 
  2. Dust mask  
  3. Protective Clothing
  4. Gloves
  5. Laser Thermometer
  6. Mastic
  7. Caulk Gun
  8. Duct Tape
  9. Foil Tape
  10. Masking Tape
  11. Paint Brush
  12. Silicone Tube
  13. Box Knife
  14. Fiberglass Insulation (foiled backed, heat resistant, the higher the r-factor, the better)

** Depending on the type of insulation you are using and what area you are working on, the materials may vary.  You might not use all the materials listed, but they may come in handy at different times during the installation of your insulation.

Step by Step Instructions

While it isn’t insulating your ductwork, taping joints in ducts should be done first. 

Below are the necessary steps needed to properly install the insulation around your ductwork in your attic, basement, and/or crawl space.  

Step 1: Choose what kind of insulation you would like to use for the job.  The most cost-effective type is foil-backed batts.  You get more for your money, but there are other options that were discussed earlier in this article. As long as it is heat resistant and has an R-factor greater than 3.5, it is a decent option for the insulation of your ductwork.  

Step 2:  Clean ductwork by wiping it down. 

Step 3: Measure the area of ductwork you will be insulating, and then cut your heat-resistant insulation to the proper size. “Measure twice, and cut once,” as the saying goes.  You don’t want to have to use more pieces than necessary.

Step 4: Wrap the ductwork with the properly sized insulation. Make sure that it fits tightly around the ductwork, but do not compress or dent the ductwork, because compressed fiberglass insulation doesn’t have as much air within the material – and air pockets help hold in heat. Also, make sure that the foil is on the outside with the fiberglass insulation on the ductwork.

Step 5: Use duct tape to secure the insulation around the ductwork.  Do this by simply wrapping the duct tape around the insulation and the ductwork.

Step 6: Using your foil tape, completely seal the seams of the insulation by using one long piece of foil tape along the entire length of the seam.

Step 7: If there are any areas that you cannot fit and seal the insulation around the ductwork, you can use mastic to seal the area via a caulking gun and a tube of mastic. Use a tool on the mastic to force it against the seam to get the best seal.

Step 8: Repeat the steps above on every section of ductwork.

Step 9: Double check all your ductwork to ensure that everything is properly covered, insulated, and there are not any exposed areas where heated or cooled air can escape via uninsulated ductwork. 

These steps described how to use flexible, foil backed insulation to wrap your ductwork in your basement, crawlspace, or attic.  You can use the same basic steps when installing rigid insulation, too.  Rather than wrapping the insulation around the ductwork, you will cut the rigid insulation to fit around the ductwork and then use the foil backed duct tape to seal it all together.  

Frequently Asked Questions

 You might be wondering about these related issues.

How much will it cost to insulate the ductwork in my basement and/or attic?

It will generally cost between $1-$2 per square foot to insulate your existing ductwork.  This price per square foot includes both the materials and labor. By DIY, you can cut the cost in half or by up to two-thirds. 

How long will it take to insulate my basement and/or attic ductwork? 

The length of time it will take to fully insulate all the ductwork in your attic, basement and/or crawl space completely depends on how much ductwork you have in your home.  It is not an extremely long process, so you can probably complete the project in a day or two.  If you hire the job out to an HVAC technician or a building contractor, you can expect them to finish the job in a day or less. 

Can I insulate my attic, basement, or crawl space ductwork myself or do I need to hire an HVAC professional technician? 

Many DIY projects require a lot of experience, but this is one project that you can do yourself.  As long as you don’t mind getting dirty, can measure, cut, and tape, this is an improvement to your home that you can save money with by handling it on your own. 

Who is the best option to hire to insulate my ductwork?  An HVAC technician or a licensed contractor? 

Either can do this job effectively and efficiently. Even a local handyman can get it done. However, if we had to choose one to do the job and get it done right the first time for maximum energy efficiency, we would choose the HVAC technician.  HVAC technicians deal with ductwork on a daily basis. 

How can I tell if I need to insulate my ductwork in my basement, attic, or crawl space? 

If you suspect that the ductwork in your home is not properly insulated you can simply go check any ducts that are located in your attic, basement, and crawl space.  If they are not covered with insulation, you can assume that they are not insulated.  Some ductwork is lined internally with insulation.  You can check this by tapping on the galvanized or aluminum ductwork.  If it sounds hollow, then it isn’t internally insulated.

Related Projects

Insulating your ductwork is hugely important for energy efficiency and the durability of your heating and cooling equipment. But there are other steps you can take to save money and keep your HVAC system working effectively.

To do this, you might want to learn more about the following topics through pages here on Pick HVAC:

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