Do It Yourself Rectangular Sheet Metal Duct

Air Supply System

• 1

  Connect a furnace takeoff to the HVAC system's outgoing plenum. The takeoff is the component that connects the duct to the furnace. The takeoff features a series of tabs along one side. Insert the tabs into the plenum. Fold these tabs up to produce a firm fit on the interior of the furnace. Use three sheet metal screws and mastic adhesive to seal the takeoff's exterior to the furnace exterior.

• 2

  Slide the plain end of the rectangular duct over the crimped end of the takeoff. Use sheet metal screws to reinforce this connection and prevent slippage. Apply mastic adhesive at the seam between these two components to further strengthen the connection.

• 3

  Add additional rectangular ducts and elbows as needed to provide the proper length of air flow coverage for the space. To do so, slide the plain ends of one duct onto the crimped end of another. Some ducts employ curled edges rather than plain/crimped edges. These are known as U-channels because of their shape. U-channels can be held together with a drive cleat by sliding the cleat over touching channels. Two drive cleats are required for this type of duct, one on either side. Secure ducts further with mastic adhesive if the gap is less than 1/4-inch wide, otherwise apply fiber tape.

• 4

  Support ducts with wire, woven polypropylene strapping or perforated pipestrap. Secure one end of the support to a wooden or steel I-beam. Wrap the support under the duct. Secure the other side to the beam. Repeat this process at regular intervals.

• 5

  Place an end cap onto the final duct to seal the system. Some end caps feature an s-cleat along the edges, which holds the cap in the duct. Push the end cap into the duct until the cleats are secure. Alternatively, some end caps feature U-channels and require a drive cleat for securing.

Air Return System

• 6

  Insert an air filter mount's connectors into the HVAC system's return plenum. This allows an air filter to be positioned between the returning air and the mechanical components of the HVAC system. Filtered air prevents dirt and particles from entering the system and increases the useful life of the mechanical components. Secure the air filter mount with sheet metal screws and mastic adhesive.

• 7

  Connect a duct to the air filter mount. Air should pass from the duct through the air filter into the system. Secure the duct to the mount with sheet metal screws and mastic adhesive.

• 8

  Add rectangular sheet metal ducts and elbows to provide adequate air handling coverage for the space. Use mastic to strengthen connections as needed. Support the ducts at regular intervals with woven polypropylene strapping, wire or perforated pipestrap.

• 9

  Place an end cap onto the final duct to seal the system. Depending upon the type of end cap and duct, either push the end cap into the duct until the cap's s-cleats hold it in place, or secure the end cap and duct U-channels with drive cleats.