How to Repair Air Conditioning Duct Work

If your duct system is damaged, expect your heating and air conditioning systems to have greatly reduced energy efficiency. All the energy that will be lost will cost more in a single season and it will exceed the price of the repair materials. So, upon seeing any damages, act immediately, and repair it to avoid spending more. 

Before directly going through the steps, I want you to be informed that there are various types of HVAC ducts. Why do I have to tell you that? Well, different HVAC duct types need different ways of repairing. 

It’s good to know what type of duct your house has. If you’re not aware, here is the list of types of HVAC Duct and some information about them:

  • Fiberglass Duct Board: This duct uses compressed fiberglass boards that have a foil outer layer. Each joint together is hold by mesh, a foil-backed duct tape, and a duct sealing compound. 
  • Galvanized Sheet Metal Systems: This starts with a plenum or a rectangular trunk line. Branch lines then run along with the systems to the individual floor penetrations. The branch lines are either made with smaller rectangular ducts or round sheet metals. What holds the pieces of the sheet metal ducts are S-shaped clips and cleats. The round sheet metal duct is held by screws together. 
  • Flex Duct: This is known for being easy to install and inexpensive. This has three layers: inner layer, fiberglass center layer, and an outer layer. The inner layer uses a spiral wire to be able to maintain its shape. The fiberglass center layer gives thermal protection. The outer layer works as a vapor barrier.

Now that you already have prior knowledge with all the types, let’s know how to repair any damaged types of HVAC duct. 

Fiberglass Duct Board

Using the fiberglass duct board does not usually need any maintenance or repair. They are made to be long-lasting and resistant to abuse. However, being exposed to excessive moisture for too long may destroy or contaminate the fiberglass. Most of the time, wet sections dry without issues. But technicians recommend replacing sections of saturated duct board due to mold concerns.

1. Drain the duct. You can do this by poking a small hole in the duct’s foil outer line. You can do it with a screwdriver. Before doing so place a bucket beneath the targeted area so once that you poke a small hole through it, water will pour directly to the bucket. 

2. Cut the damaged section. Using a non-serrated knife, force through the duct and cut out the damaged area/wet area. 

3. Create the replacement patch. You can base the measurement on the cutout or the hole with a tape measure. Apply the measurement on the new sheet of duct board. Cut the board with a non-serrated knife. 

4. Install the patch.  You can install the patch by pressing the patch on the hole until its foil backing fits with the existing duct’s surface. Then, apply a piece of foil-backed duct tape on the seam. Press it with a squeegee. Cover it with a mesh. And lastly, using a paintbrush, coat the mesh with a 1/8 thick layer of duct mastic. 

Sheet Metal Duct

Homes in northern climates often use galvanized sheet metal ducts. This helps to keep the flooring warm. The main problem is that occasionally, the sealant allows the heated air to escape because it loses its grip.

1. Expose the Leaking Seam. On both sides of the area, you are planning to repair, loosen the hanging straps or brackets. Lower the duct to be able to examine the leaking joint thoroughly. Leaks can easily be solved with additional sealant normally. But if we’re talking about large gaps, you should expose and inspect it. If S-lock is missing or incorrectly installed, it might be the cause of the gap. To resolve, take it apart then correctly reconnect it.

2. Repair the S-lock. If applicable, cut the old mastic with a utility knife from the perimeter of the joint. Remove all the screws that might be holding the S-lock in its place. Pull the tabs on the ends of both drives after straightening it. Separate the joint after doing so. Tension might prevent it from being completely separated. Slip the old S-lock from the joint. With a screwdriver, open the S-lock then put it back to its place. Each flat metal on the sides of the duct should slip into the gap created by the screwdriver. Lastly, by using a hammer, install the drives. 

3. Seal the duct joint. With a 1/8-inch thick layer of code-approved cut mastic, cover the joint. Use a paintbrush to do so. There is mastic designed specifically for galvanized sheet metal ducts. 

Flex Duct

Sometimes, you will see an exposed air conditioning duct collar during home inspections. This might happen because the pressure forces the insulation and outer liner away from the collar. By having an exposed collar, expect that the efficiency of your system’s energy is greatly reduced. 

1. Solve it. Next to the slipping connection, add a hanger strap to relieve any tension. Then, place those straps throughout the duct run. 

2. Disconnect the Loose Liner. With pliers or wire cutters, cut the duct strap. Pull away the insulation from the connection. Then, to properly cover the insulation, adjust the outer liner. 

3. Attach the outer liner. On the layer’s butt edge, apply mastic. Mash the material with each other until it gets sealed by the mash. Lock it with a duct strap in place. Lastly, apply mastic to cover the outside of the joint. 

These are the common damages that may occur on your AC duct. These solutions might provide a big help in case you relate to any of those issues. Remember to check what type of duct do you have before doing any actions. It’s also not bad to ask for professional help in case you need some.