How To Replace Damaged Rectangular Ductwork In Your Home

You may have exposed ducts that have suffered dents or other damage, or have been exposed to extensive moisture and are rusting away. Compromised ducts will leak heated or cooled air, severely impacting the efficiency of your heating and air conditioning systems.

Fortunately, it's relatively easy to replace ducts, but it can be a dirty job, especially if the ducts have been in place for a long time. There is also the danger of being cut when working with razor sharp sheet metal. 

However, if you are not easily deterred by these revelations, here's what you need to do:

What do you need to replace duct work?

The Ducts

You must first measure both the length and width of the ducts, then determine the overall length of the combined ducts that need replacement. Rectangular ducts are sold in various lengths. Longer lengths require fewer connections but are more difficult to install overhead, while shorter ducts require additional connections but are lighter and less cumbersome in tighter spaces.

Metal snips

Also called aviation snips, you will need them to cut connectors to size, so choose snips that are at least 18 gauge capacity, even though the ducts themselves are much lighter. The connectors are hemmed in different ways and are then more difficult to cut. If you need to cut ducts to achieve the desired length, you will also need the snips to cut individual ducts to size.

Seamer Tongs

This tool is used to bend a hem on the edges of the ducts for connection purpose.

Water Based Duct Sealant and small caulking gun

Don't use a solvent based duct sealant in your home. They are highly flammable and can cause health issues from exposure.

Silver duct tape

Don't use the traditional multi-use gray duct tape. It is ineffective for sealing duct connections.

Slip and drive connectors

These lengths of hemmed metal are used to connect ducts together. Drives are flat strips of metal that are hemmed in on both sides, while slips are hemmed into an "S" shape.

Hammer and flat screwdriver

Drill with screw chuck and 1/8" (#30) bits

Dust mask and safety glasses (optional but recommended).

Removing the old ducts

If you are moving a line of connected ducts, it may be easier to lower the entire line of ducts to the floor and disconnect the there. You will see that the ducts are suspended by metal straps that are screwed into the sides of individual ducts. When these screws are removed, the ducts will fall, so be prepared. If you are doing the project by yourself, it may be best to take the ducts apart first.

You will see slips used to connect the longer sides of the ducts, and drives connected the shorter sides. The drives are cut longer than the actual sides of the duct and bent over the edges to cover the ends of the slip connectors.

You can use a hammer and screwdriver to pry away the edges of the drives, then use the tongs to pull them away from the ducts. You will notice that the shorter ends of the ducts are hemmed outward approximately one-half inch. You will need to use the tongs to bend the edges of your new ducts in the same manner.

Connecting the ducts

The slip connector is cut slightly shorter in length than the long sides of the duct. They are then hammered lightly onto the longer sides of the duct until they are fully seated. Because slips are "S" shaped. The longer sides on the next length of the duct are pushed into the opposite hem of the slip connection until fully seated. The slip connection is then secured with screws.

The drive connectors are cut two inches longer than the shorter sides of the duct. They are then hammered into place over the hemmed edges of the ducts. When they are evenly positioned. use the hammer to bend the ends of the drives over the edges of the ducts. You must then screw the hangers into the new ducts to secure them.

Seal all connections, especially corners, with the water based duct sealant. You can apply silver duct tape around the connections after installation is complete and the duct sealant is fully dry. Contact an HVAC installation company for more information and assistance.