Ducts are a great first big DIY insulation job.

The benefits are very high for your total home insulation.

• 20-40% of the heat produced by a furnace generally does not get to a room.
• The same rate of loss applies to air conditioning ducts.
• Studies have shown that 80% of houses have major air leaks and other problems with air ducts.
• Insulated ducts will also reduce condensation that causes mold and water damage. Furnace and A/C noise will be less.
• Do duct insulation installation before attic insulation if any of your ducting is in the attic.

Insulating ducts is a three-step process:

• Inspect and document.
• Assemble insulation materials and tools.
• Do the work with a plan.

Step One: Inspect and document your present ducting

A complete review will save time and money

• Get the best portable light(s) you can, a small digital camera with a flash, a measuring tape, and a small pad to make notes.
• Measure diameters and lengths. Look for compressions and kinks. Count and check registers. Note seams and joints that are not well sealed. Take enough pictures so you can efficiently evaluate and communicate your needs.
• Be sure to check around all joints, boots, registers, cold air returns, and the plenum, which connects the furnace to the ducts. Estimate the length of all cracks, seams, and joints that can be sealed or caulked. Check for places where extra duct hangers would help straighten or support a duct.
• Large leaks between the plenum and the ducts are very common. It is also common to find ducts that are partially disconnected from the boots that attach the ducts to the room vent registers.
• Make note of all possible leaks. Even very small leaks can add up to major losses in energy efficiency. If in doubt, plan to fix it.
• Asbestos was commonly used for home insulation decades ago. It usually looks like thick grey paper. Asbestos is Very toxic. When disturbed it will release microscopic fibers that will get into lungs and cause serious disease and/or death years later. If you see asbestos, then leave it in place and consult with a qualified insulation contractor to either safely seal it in place or get it properly removed.
• Write out your questions on tasks and start a materials list.
• If your present ducts are not insulated or are damaged, it may be much simpler, quicker, and better to replace them with new pre-insulated flexible ducting.

Step Two: Select & assemble insulation materials

Materials can be divided into the following categories:

• Tape
  • Never use standard duct tape. It does not last long and is a common cause of air duct failure. Heat changes cause the cloth backing to shrink and the adhesive to quickly fail.
  • Good quality tape is absolutely essential for an effective duct insulation installation. They are sold at large hardware stores and online.
  • Tape for ducts that will do a good job that lasts include:
    • Foil backed butyl duct tape:
      • Foil-Grip 1402 (Mfg. by Hardcast) is good for rigid steel, board, and flexible ducts
      • Nashua 558C and Polyken 558CA brands (both made by Berry Plastics)
    • Oriented Polypropylene (OPP) tape:
      • OPP is a strong film backed with acrylic adhesive and is also a good choice. An example is FlexFix Tape (Berry Plastics).
    • HVAC Rated Aluminum Furnace tape:
      • Use to seal seams of the furnace, the furnace fan housing, and where the furnace joins the plenum.
• Mastic sealant
  • Mastic sealant is commonly used to seal seams and joints. It is put it on as thick as a nickel with a single use paintbrush. The mastic is gooey and non-hardening. Wear gloves and old clothes. Mastic is messy.
  • Mastic requires the use of fiberglass mesh to cover any seems with a crack wider than 1/8". The mesh gives the mastic a stronger structure and greater thickness.
  • Fiberglass mesh is a few inches wide and comes in small roles.
  • Some quality mastics include:
    • Polymer Adhesives Air Seal # 22,
    • Mc Gill Air Seal Uni-Mastic 181 Duct Sealer,
    • RCD Corp. #7 Mastic,
    • Versi-Grip 181 Duct Mastic.
  • A much simpler method for sealing most joints and seams with foil backed vinyl foam insulation and tape is described below.

• Caulk
  • Good quality Urethane and Silicone caulks are fine for sealing cracks between registers and surfaces of walls, ceilings, and floors.
  • Caulk is simple, safe, cheap, effective, long lasting, easy to work with, and is highly recommended for DIY insulation installation.

• Canned foam insulation sealer
  • Caution is required when using polyurethane foams for home insulation projects because of several safety concerns. 
  • They often emit hazardous chemical compounds.  Be Very careful to avoid getting a drop splattered in your eye. 
  • Great Stuff (made by Dow Chemical) is one of several brands that offer foam insulation products in spray cans that can seal large and small cracks and holes. 
  • An extension handle for the can will make application easier. 
  • Over expansion during the curing time of at least several hours is still an issue with many products.  Foam insulation can distort the shape of the surface you are trying to seal.  Over expansion of polyurethane foam insulation in walls can cause bulges in walls and has cracked window frames.
  • With careful and safe practices, spray foam insulation can be very useful when properly applied in appropriate situations.

• New pre-insulated ducts
  • The most common type is a wire coil set in a strong plastic film that is insulated with fiberglass and covered with a plasticized aluminum foil. 
  • They come in all common duct sizes and generally have an R-6 or R-8 rating.  Several brands are available at large hardware stores and online.  The cost is quite reasonable.
  • Getting the higher R-8 or even R-10 rating is recommended.  The insulation installation is the same and the extra insulation energy efficiency is worth the small additional cost. 
  • Insulation installation with new pre-insulated ducts is relatively simple, cost effective, and highly recommended for a DIY insulation project.

• Insulation for existing ducts
  • If you have decided to not replace existing ducts with new pre-insulated flexible ducting, be sure to get at least an R-6 rated insulation product.  R-8 is worth the small additional cost. 
  • You can choose between several common types of DIY insulation material for insulating your existing ducts.

• Duct insulation sleeves. 
  • Duct insulating sleeves can be wrapped around existing metal ducting to achieve up to R-8 insulation.  They are pre-sliced and often have an adhesive strip to make insulation installation easier. 
  • Insulating sleeves are commonly made from foam, bubble wrap, and fiberglass.  They typically have a foil outer surface.
  • MasterFlow and Frost King both makes duct sleeves with an R-6 and R-8 rating.  Both are sold in large hardware stores and on the Internet. 
  • Sheets of the same fiberglass or other insulation products are available with or without a foil backing.  Sheets or duct sleeves can be cut to make pieces to fit corners, boots, plenum, etc. 
  • One or more layers of insulation material can be installed to achieve a sufficient R rating.  Be sure to seal all ends and seams on each layer to completely eliminate all potential leaks before applying any additional layers.
  • Foil backed self-adhesive foam insulation can make it easier to do a good job of insulation installation on irregular shapes.

• Vinyl foam with aluminum facing
  • Thermwell (made by Frost King) is a self-adhesive strip of foil backed vinyl foam insulation.  It comes in rolled strips a foot wide and 15 feet long.  It is sold in large hardware stores and on the Internet.
  • This product is simple to apply.  It can easily be cut to fit the irregular sizes and shapes of existing ducts, boots, plenum, etc., which makes insulation installation relatively simple, even if the ducts are being insulated with another product.
  • It provides an easy and effective way to seal joints and seams by first wrapping them well and then securing all edges with tape.  Fully overlapping material two inches at joints will give you a much better insulation installation and total energy efficiency.
  • Since the product is thin, use additional layers to increase the R rating and help seal the seams in the underlying layer of insulation. 
  • Vinyl foam is very good at dampening sound.  And, there are no fiberglass insulation fibers to breath.

• Cotton or fiberglass strips with foil backing
  • Several home insulation manufacturers make roles of cotton or fiberglass with aluminum foil outer surface that is generally less than 1 inch thick, a foot wide, and 15 to 20 feet long. 
  • It is hard to get a good job on ducts with using this type of insulation product because of the many long seams. 
  • However, if you are willing to completely seal all seams and ends with tape, without compressing the insulation, then you can get a decent job of insulation installation.
  • This type of product can be cut to size and effectively used for insulation installation on irregular shaped boots, junctions, etc., and to insulate the joints between sections of pre-insulated ducting, if it is very well taped and not compressed.
  • Frost King foil backed cotton insulation strips have an rating or R-4.  The fiberglass products do not have a rating.

• Foil backed bubble wrap
  • Do not use cheap bubble wrap reflective insulation to simply wrap ducts.  There are a number of reasons including poor energy conservation and potential moisture problems created by temperature changes.
  • If you want to use reflective insulation, then get the better quality Prodex Brand which is sold online.
  • An effective job requires an air gap between the surface of the duct and the reflective surface of the insulation.  Without the air gap, the insulation does not work well. 
  • The required air gap makes insulation installation more difficult.  The air gap is made by gluing or taping strips of the reflective insulation to the surface of the duct and then gluing or taping the reflective insulation on top of the strips so that the surface of the reflective insulation does not touch the ducts.  A second layer of reflective insulation can be added by repeating the same process with a second air gap. 
  • DIY insulation installation of ducts does not have to be this hard.

Step Three: Doing the work with a plan

Assemble and check all tools, materials, and lighting. 

• It will help to have at least two pieces of half-inch plywood to use as work platforms.  Two by four foot is a versatile size.  Although one person can do the insulation installation job, it is a lot easier with two.
• First make sure the connections at registers and boots are tight where they meet the wall, ceiling, or floor. 
• Then do the caulking of all registers and boots and the sealing of all joints and seams, before taping them as needed.
• This is tedious and hard work.  Doing this step well is very important to getting an insulation installation with excellent long lasting energy efficiency. 
• Be certain that joints between sections of rigid metal ducts are attached with at least two well-set metal screws if the joint is not secured with a compression fastener. 
• Make sure the furnace filter rack is tight so that outside air is not drawn in from the seams. 
• It is crucial to seal all seams on the cold air return before completing its insulation installation.  In addition to loss in energy efficiency, air leaks in the cold air return can create an air quality control problem by drawing in air with pollen, dust, or fiberglass insulation fibers from the attic or crawl space. 

Installing new pre-insulated flexible ducting.

• This is a simple insulation installation. 
• Just cut the sections to fit and then tape them in place. 
• Metal joints are made to easily join sections of new pre-insulated ducting.  The metal joints are sold separately.
• Using foil backed self-adhering vinyl foam insulation makes it easy to cut pieces to size for insulating and sealing the joints between sections of ducting.  Use extra layers to increase the R-value.  Be sure to wrap each joint with ample tape without compressing the duct insulation. 
• The foil backed vinyl insulation makes it simple to do a good job of insulation installation on the irregular shapes of the register boots, plenum, etc.

Insulating ducts with foil backed vinyl foam

• Just wipe lose material off the duct surface, cut the material to fit a section, and press to apply. 
• Do extra layers to increase the R-rating and energy efficiency.
• Cut material for the second and other layers so that new material completely covers the joints on the underlying layer of insulating material.  Overlap insulating material at the joints.
• Do the same process of insulation installation with the boots, plenum, cold air return, etc.
• Finally, use amply tape on the joints between sections of insulation material. 
• This product makes DIY home insulation installation on ducts relatively simple for smaller jobs.  Material cost could become a factor on larger jobs.

Installing foil backed fiberglass duct sleeves

• Wrap the duct with the sleeves and overlap the insulation material at least two inches where the sections of insulation meet along all edges.
• Make the fit tight without compressing the insulation.  Cut pieces to cover all duct surfaces and completely eliminate any gaps in the insulation installation. 
• Carefully taping all seams, joints, and ends is critical to getting a good job of insulation installation. 
• Even very small gaps in the insulation will allow heated air to get out after contact with the outer surface of the duct will greatly reduce the energy efficiency and the value of your home insulation project.
• Insulate the boots, plenum, etc. with pieces cut from sheets of insulation material.  Doing double layers and using abundant tape are worth the effort to get a really good job that will save money and increase comfort for many years.
• Tape much wider than the joint of sections.  The extra taping can help provide many years of high-energy efficiency service without future leaks and separations. 

Summary

• The total energy efficiency of your home insulation will be greatly improved by doing a careful DIY insulation installation. 
• Better energy conservation will improve comfort and save money.
• Do your attic insulation installation after you have done the ducts.
• For more information: download Duct Sealing, a free brochure from the US Department of Energy.