How to Replace Sheet Metal Ducts in Air Conditioning With Flexible Ducts

Disassemble the section of sheet metal duct that you wish to replace with a flexible duct. Unscrew the sheet metal screws from each seam and remove the section of duct.

Measure the length that the flexible duct will span. Add the required allowance to the measurement for your flexible duct. For example, if the run is nearly straight, add 6 inches. Add 12 inches for each 90-degree bend.

Cut your flexible duct to the required length. Use a duct knife or utility knife to cut through the outer liner, insulation and inner liner. Cut the reinforcing wire with a wire cutter.

Roll back the outer layer and insulation on each end. Slide the inner liner 1.5 to 2 inches over the end of one duct. Wrap a cable tie around the inner liner and cinch it tight to secure the liner to the duct. Tighten with your tensioner tool. Repeat the process with the other end of the inner liner on the other duct.

Unroll the insulation and outer liner gently on each end until it completely covers the inner liner. Wrap a cable tie around the outer liner and insulation and cinch it tight. Tighten with your tensioner tool. Repeat the same process on the other end.