How To's - How to Insulate Ductwork

How to Insulate Ductwork

There are many reasons to insulate ductwork. The big one is that you’ll save money. Ventilation ducts in attics, crawlspaces and basements that are not insulated warm up in the summer and get cold in the winter. This increases the amount of time your system needs to run to warm and cool your home.


Ductwork insulation prevents this problem—and it saves you money in energy costs. It also keeps ducts dry. This has the added benefit of keeping ducts free of mold. Sealing the ducts prior to wrapping them with insulation reduces air escape, ensuring the cool or warm air gets where it needs to.


If your ducts aren’t insulated, it’s worth doing. Fortunately, it’s a simple DIY job. Let’s get started…

Tools and Materials Needed to Insulate Ductwork

You don’t need a lot of tools for the job. You do first want to identify the materials you will need.


If you only need to wrap the ducts, you’ll need to measure to determine how much duct wrap you will need. Duct wrap is a specific fiberglass duct insulation product made specifically to insulate ductwork. It has an outer foil barrier which is there to keep moisture out.


Most building code calls for R-8 insulation to insulate ducts, but you should always check with your building inspector.


Expert tip: if you can’t find R-8 at your local home improvement center, check an HVAC equipment wholesaler or supplier.


Now, you might think you’ll also need duct tape. No, you won’t. You need a special aluminum duct tape to seal the insulation seams and any long seams on the ducts (depending on your system).


You should also check the bends and turns in your ducts for potential leaks. This is common. A duct mastic can be applied with a brush to seal the seams before you insulate.


Here is a quick list of materials and tools you’ll need for this simple project.


Materials Needed to Insulate Ductwork


  • Duct Insulation
  • Aluminum duct tape
  • Duct mastic (optional)
  • Steel wire, to take stress off the seam


Tools Needed to Insulate Ductwork


  • Tape measure
  • Utility knife
  • Safety glasses
  • Dust mask
  • Work gloves


As you’ll be working with fiberglass insulation, you will want to wear long sleeves and long pants.


You may also want or need the following tools, depending on whether you will need to remove brackets, apply mastic, give added support to the insulation or be working in an attic and crawlspace.


  • Drill—cordless is best
  • Knee pads—in an attic or crawlspace you’ll be kneeling a lot
  • Pliers—makes bending steel wire used for added support easier
  • Paint brush to apply mastic

How to Insulate Ductwork

Prep your ducts first and make accurate measurements and you’ll make your house energy efficient in no time. Here’s how to do it.


Step 1. Prep the ducts. Apply mastic at bends or corners to prevent air escape. Along any long seams, which can be common on circular ductwork, seal with aluminum duct tape.


Step 2. Cut the insulation. Measure the circumference of the duct and add 2-3 inches. You can do this by wrapping the duct tape (with the adhesive still covered) around the duct. You add the extra couple of inches so you can create a tab which will make taping easier.


You also need to measure the length of duct insulation needed. The longer the piece, the better insulated the duct will be. If you have duct hanger brackets in the way, it may make sense to remove them when you wrap the duct. Of course, you will want to do it one section at a time and support as needed. Once the section is wrapped, you will put them back.


Cut the insulation to the length needed. Then peel the foil back from one side an extra two inches or so, fold and then cut the excess insulation. You now have a tab.


Step 3. Wrap the duct. Take the insulation and wrap it around the duct. Use the tab you created to create a straight seam. Tape.


Step 4. Apply wire. Relieve stress on the seam by wrapping the wire around the insulation every two feet.


Step 5. Reattach brackets (as needed). Once you have wrapped the duct, take the bracket, cut a hole for it in the insulation and feed it through the hole and reattach securely. Use tape to seal the bracket and the holes completely.

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