How to Put in Duct Work


Duct work can appear challenging to install. It is not a well-known trade and not many people take on this task themselves. However, duct work isn't actually that hard to install. Once you understand the principles on how to connect it and cut down joints, it is a moderately easy task. The typical homeowner will probably have to buy some specialty tools to put in duct work, but the cost savings is well worth it.

Things You'll Need

  • Hammer
  • Aviation snips
  • Hand seamers
  • Pipe crimper
  • Screwdriver
  • Cordless drill
  • Metal hanging strap
  • Sheet metal screws
  • Safety glasses
  • Gloves


  • Separate your square and round duct work. Usually the main trunks are the square duct, so those will be installed first.

  • Look at the end of a square duct joint. You will see that two sides have a raw metal edge. The other two sides have a folded over edge. You will use s-slips and drive cleats to join your duct together. S-slips when viewed from the edge have two "pockets" that look like the letter "S". These "pockets" allow duct work to slip together by overlapping the raw metal edges. Drive cleats hold the two joints of duct together by preventing the folded-over edges from coming apart. See reference 1 for pictures of s-slips and drive cleats. Cut two s-slips for the raw edge. The s-slips will be cut 1/2 inch smaller than the raw edge's length. Cut two drive cleats for the folded over edge. These will be cut two inches longer than the folded over edge.

  • Put a set of s-slips on one end of duct. Slide the raw edge of another piece of duct work into the other slots on the s-slips. The folded-over edges should now be butted up together. Take a drive cleat and pound one up each folded-over edge. They should stick past the s-slips about one inch on each side. Pound these over with your hammer.

  • Hang your duct with one-inch metal straps. Anchor the straps to structural members and screw it into the duct. Continue putting the square duct together and hanging it until it is finished.

  • Move on to the round duct. Round duct is much easier to install than square duct. Take a crimped end and insert it into a non-crimped end. It should lap about 1 to 1 1/2 inches.

  • Screw the round duct together with sheet metal screws. Use four to six screws per joint depending on round duct size. The bigger the round duct, the more screws you should use to hold it together.

  • Hang your round duct with one-inch metal straps. Make saddle hangers by screwing the strap to the structural member, then loop it under the duct. Then screw the other end to the structural member. Continue assembling and hanging your round duct until complete.

Tips & Warnings

  • If you need to cut a joint of square duct, you will need to make the folded-over edge to receive a drive cleat. Cut the duct all the way around, notch the corners out one inch, and then use your hand seamers to fold two sides over 1/2 inch. It will almost look hemmed, but not be pressed tight.
  • If you need to cut a joint of round duct, you will use your pipe crimper to put a crimped edge on one end of the pipe.
  • Sheet metal duct work is very sharp. Wear gloves at all times while handling sheet metal, as it can cause very severe cuts.

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