How to Properly Install Flexible Ductwork

What You'll Need
Flexible ducts

Flexible ductwork is a very popular because it is easy to install, and has great insulation potential. Flexible ductwork is often made from flexible metals such as tin or aluminum, also metal fiberglass, or plastic. Some kinds of flexible ductwork can also be made from vinyl insulation, which is extremely easy to fit on your own. Complications such as sagging and resistance are avoidable, so there is no need to call in professionals to do the work for you, instead, by following a few basic instructions, you can complete this project quickly and efficiently yourself.

Step 1 - Planning the Ductwork

You may find it easier to place the plenum, which is the very end of the duct entrance, usually found near the furnace or air conditioner which will use the ducts. You can then add a line of ductwork until the discharge fixture can be fitted to the outside. When you are measuring the ductwork prior to installation, remember that you will need to have regular support joints fitted in order to support the flexible material. If you don't put in enough of these joints, you may find that your ducts don't function properly. You should allow for the smallest amount of duct work, keeping connections to the minimum length, in case you need to relocate the terminal devices in the future. Take care not to place your duct work too near any strong sources of heat, such as that in a HVAC device, and avoid curling the duct around a sharp point.

Step 2 - Installing the Ductwork

Once you have an idea of where the ductwork should go, start with the plenum, and screw that into position using duct brackets and suitable screws. You should then add the first piece of ductwork, and screw it so that it fits tightly into the plenum. Add a support joint, and then place another piece of the ductwork onto this. Your support joints must be at least 4 inches long, and be beaded both sides. Pull both sides of your ductwork so that the insulation is free of the ends, and then wrap duct tape around both pieces. Attach the joint into the middle, and secure with more duct work. Pull down the insulation so that it covers the core. Continue throughout the line until air can be discharged at the exit. You may need to add caulking around the edges of your ducts to keep the air sealed into the piping.

Step 3 - Precautions

Flexible duct work can be easily damaged by heat sources such as pipes, hot air vents, and chimneys, so take care when positioning your ducts around this area. In addition, sharp corners, such as might be found in floor joists or on the underside of stairs, can cut into the duct pipe. As well as avoiding these dangers, your flexible ductwork should not be fitted into concrete, buried below the ground, or come into contact with an earth surface. Sagging can be avoided by using padded hangers suspended on wire from the ceiling, or by resting on ceiling joists.