Most ductwork is just a metal tube with nothing to prevent the escape of the heated and cooled air that is passing through it. This translates into lost heating and air conditioning efficiency. To improve the performance of this system, it is necessary to wrap the ductwork with some type of duct wrap. Wrapping your ductwork is not always a pleasant job because of where the pipes may be located. You may be in a dirty crawl space, a very hot attic, or some tight spaces.
Fiberglass insulation is the easiest type to work with for the beginner.
Several varieties of insulation will work for duct wrap. Fiberglass insulation with a moisture shield is the most common type of insulation used for this purpose. It is light weight, easy to cut, and comes in several different R values. When using fiberglass insulation, make sure to wear a mask to keep from inhaling the fibers and dust associated with this product.
Figure out how much insulation is needed before you buy it.
Measure the circumference or perimeter of the ductwork. You will need to know the over length of the ducts. Use these measurements to compute the amount of insulation that will be needed to wrap the ductwork. Add 20% to the total to allow for waste and extra for overlaps at the seams. Buy plenty of duct tape to tape the insulation together as you install it. Also, cover any leaks you discover in the ductwork with duct tape before wrapping it.
Lay the insulation on a flat, clean, open surface to unroll it.
Unroll several feet of insulation. Use a utility knife to cut through the insulation and the wrapper. Cut each piece of insulation four inches longer than the circumference or perimeter of the duct being wrapped.
Use the first piece of insulation as a training opportunity.
Wrap it around the duct with the moisture barrier on the outside. Do not pull it overly tight. It is the air space within the insulation that gives it a good R value. If you pull it too tight, the fibers will be compressed and you will lose some of the insulation benefit. Cut away any excess insulation. Use this adjustment to get the correct size for all of the other pieces of wrap to be cut. Tape the ends of the wrap together to hold it in place.
Follow the pattern from the first piece to complete the job.
Wrap the second piece in the same way as the first one. After the ends are taped, tape the seam between the two pieces of wrap. Continue this process until the entire ductwork system is wrapped. Tape small pieces of insulation into areas where the run changes direction or the pipe size changes to fill in all of the gaps that can be left.