How to Replace a Round Duct With a Flat Duct

Furnace ducts route warm or cool air throughout a home. Ducts may be round, flat and rectangular, or a combination of the two. Round ducts are typically installed below floor joists in basements where headroom is not always an issue. However, when the low and exposed round ducts interfere with your remodeling plans, you can install an adapter that connects the round duct to a flat, rectangular duct which can be routed between the floor joists. A few tools and basic do-it-yourself skills are required.

Phillips screwdriver
Flat-head screwdriver
Power screwdriver
Self-tapping metal screws
Aluminum foil duct tape

Instructions

- 1
  Turn the furnace electrical power off at the main breaker panel to ensure the furnace will not be operated while you are working on the ducts.
- 2
  Remove any old duct tape at the duct joint you are separating.
- 3
  Inspect the joint for metal screws. Duct joints are usually secured by metal screws to prevent them from coming apart inadvertently due to stress or vibration.
- 4
  Remove the metal screws by turning them counterclockwise using the appropriate screwdriver.
- 5
  Pull the ducts apart from each other. The inner duct is slightly smaller in diameter than the outer duct and will be inserted approximately 3 to 4 inches.
- 6
  Connect the round end of the flat rectangular duct adapter to the round duct from the furnace. Insert the adapter until it is fully seated.
- 7
  Install self-tapping metal screws through the duct joint using a power screwdriver. Drive the screws into the metal duct clockwise.
- 8
  Connect the new flat duct to the rectangular end of the adapter. Secure the joint with screws.
- 9
  Seal each duct joint seam with several turns of aluminum foil duct tape.
- 10
  Repeat Steps 2 through 9 on remaining ducts.

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