How to Join Sheet Metal Ductwork

Written by william rockwell
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How to Join Sheet Metal Ductwork
Joining pieces of sheet metal ductwork can be as easy as slipping one end into the other and securing an O-clamp. (Hemera Technologies/ Images)

Joining ductwork is an essential part of installing or replacing a heating or cooling system. There are several different ways to complete the task, each with advantages and disadvantages. Professional installers use rivet guns and notched installation techniques, but a simple patch job is possible with duct sealant or even duct tape. There are even some twist lock systems available designed for installation without the need for extra hardware or tools of any kind.

Skill level:
Moderately Easy

Things you need

  • Rivet gun
  • Metal rivets
  • Duct tape
  • Tin snips
  • Heavy work gloves
  • O-clamps
  • Duct sleeves
  • Duct sealant
  • Screwdriver

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    Joining Ducts with Rivets

  1. 1

    Slip one end of the duct sleeve over the end of one of the two duct pieces you wish to join. Slip the other duct piece into the open end of the sleeve. The sleeve should cover the ends of both pipes by at least 2 inches.

  2. 2

    Drive rivets into the sleeve along the outside edge of one sleeve at 2-inch intervals to join the sleeve to the duct it is covering.

  3. 3

    Drive rivets into the other piece of duct, attaching it to the sleeve in the same manner as the previous step.

    Joining Ducts with Notches

  1. 1

    Fit two lengths of corner pipe together with a modified butt joint. Where the ducts will come together, cut the side of one duct completely out with tin snips so that the other piece of duct can slip inside, creating a 90-degree corner.

  2. 2

    Score the edge of the uncut duct with the tip of the tin snips. Do this at the interior point where the joint is made. Make sure the score mark runs from the top edge of the duct to the bottom so you have a point of reference when making the next cut.

  3. 3

    Withdraw the scored duct and cut it to within one inch of the inside of the joint. Make sure to remove this piece of the duct. There will be no airflow through the corner joint if it is not removed.

  4. 4

    Make two 1-inch cuts at the edges of the overlap in the duct. The overlap is the 1-inch interior piece that you left on the inside of the joint past the score mark in the previous step. Bend this piece of the duct to a 90-degree angle so the lip created is on the outside of the ductwork.

  5. 5

    Slip the 90-degree notched edge into the open duct.

  6. 6

    Seal the edges of the joint with duct sealant. Use a piece of duct tape to create the initial seal if there is a hole too large for the sealant to cover.

    Joining Duct with O-clamps

  1. 1

    Slip a duct sleeve over one end of a round duct pipe.

  2. 2

    Slip two O-clamps over the sleeve.

  3. 3

    Place the second pipe into the sleeve.

  4. 4

    Move the O-clamps into position so that one clamp is over the sleeve on each pipe.

  5. 5

    Tighten the O-clamps by turning the securing screws.

Tips and warnings

  • Always wear heavy-duty gloves when working with tin snips and duct work. The edges are extremely sharp and can cause deep lacerations.

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