How to Replace Ductwork

Ductwork in the attic
Ductwork in the attic (Image:

Replacing the ductwork in a house is a tough job whether it is located under the house or in the attic. Even then, the restricted space will cause the job to go slow, so plan this when there is plenty of time to do it correctly. Take every precaution to protect yourself from the fiberglass insulation that you will be working around. It can be a skin irritant, but it can also cause damage to your lungs. It is highly recommended that some sort of breathing apparatus be worn, as well as skin and eye protection. The most common ducts being installed are flex-ducts. These will come in a box and spread out like an accordion. Along with the flex ducts, be certain that enough insulation is included to wrap the ductwork in to avoid leakage and condensation. Some flex pipe ducts come with insulation already installed.

Things You'll Need

  • Ducts
  • Insulation (if needed)
  • Utility knife
  • Duct tape
  • Plastic ties (if under the floor)

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Place new ducts in strategic places throughout the duct system. This will keep you from running back for new boxes of the ducts.

Locate a good starting point, and remove the insulation from the existing ductwork. Determine how the ductwork was assembled, and disassemble it as carefully as possible. If in an attic, set it aside to be out of the way until you are ready to climb out of the attic.

Start from the main trunk and attach the new duct, following the length of it until you reach the register to the room. Add another section of the flexible duct if needed by slipping one section into the other. Do not go deeper than 12 inches, and wrap the joints in duct tape. Secure the ductwork to the register boot according to the manufacturer’s instructions.

Wrap a good seal around the joints with the duct tape. Check for possible leaks.

Repeat Steps 2 through 4 until all ductwork is replaced. If ductwork is under the floor, secure it to the floor joists with the plastic ties. Place one about every 18 to 24 inches.

Tips & Warnings

  • Always wear protection when working with fiberglass insulation.
  • Keep plenty of duct tape nearby.
  • If working under the floor, keep plenty of plastic ties within reach.
  • Some ducts will require you to peel back the insulation to make a joint.
  • Do not breathe in fiberglass insulation, as it can cause injury to your lungs.
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