Multiple Roll Discount
Duct Insulation

10 to 30% of the energy used to heat and cool the air is lost through the duct surfaces.

The Best Duct Insulation

1. Blocking the different types of heat transfer
2. Duct insulation levels
3. Prodex Total versus fiberglass batt
4. Benefits of using Prodex Total insulation
5. Installating Duct Insulation
6. References

Good air duct insulation, properly installed will improve the energy efficiency of your home and save you money. Common terms for duct insulation include: heating duct insulation or ductwork insulation. The latest advance in duct insulation is using reflective insulation to control conductive heat transfer, radiant heat transfer and condensation in one product - Prodex Total heating duct insulation

Insulate ducts located in the unconditioned spaces of your home like the attic, garage, crawlspace or unfinished basement. Air ducts supply conditioned air from heating or air conditioning equipment into the living spaces of your home. These ducts are usually made out of thin sheet of metal that easily conduct heat. Air ducts can lose energy in three ways: by conduction of heat through contact of the material with the surrounding air, by radiation as all materials radiate energy, and by leaking through cracks and seams. According to the US Department of Energy, "Due to extreme winter and summer temperatures in unconditioned spaces, 10 to 30 percent of the energy used to heat and cool the air is lost to conduction through the duct surfaces."

When ducts lose heat through conduction, rooms at the end of long duct run may experience cool blows during winter because the air that reaches them typically has lost its intended temperature by up to 10 degrees. In this case, running the heat can effectively cool the room rather than heat it. Similarly, cool conditioned air must maintain its temperature or it will fail to cool the room at the other end. Estimates are that 55 degree air moving through an un-insulated sheet metal duct will pick up degrees for every 100 feet it travels.

In addition, up to 30 percent of furnace heat can be lost through cracks and seams in un-insulated duct work. In order to maintain temperatures at a constant level, heating and air conditioning equipment must compensate for this heat loss or gain by conditioning additional air. Un-insulated or poorly insulated ducts will reduce the efficiency of your heating and cooling systems and increase your energy bills.

Blocking Different Types of Heat Transfer

Loss of Energy Through Conduction

Conduction is the direct flow of heat resulting from a physical contact of a warmer body with a cooler body. The transfer of heat by conduction is caused by molecular motion in which molecules transfer their energy to adjoining molecules and increase their temperature. An example is heat transferred from a hot burner to a pot through direct contact. 

The denser the material is, the better it will conduct heat. Because air has such low density, air is a very poor conductor and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubble and the building cavities like the attic.

Loss of Energy Through Conduction Radiation

Radiation is the movement of infra-red energy through air or a vacuum. All surfaces above Absolute Zero emit radiation to different degrees including a stove, a ceiling and fiberglass insulation. Radiation energy travels outward from a source in all directions at near light speed until it is absorbed by a body in its path, whereupon it is transformend into kinetic energy - or heat -within the intervening body. When this energy strikes a dense surface, it is absorbed and increases the temperature of that surface.

An example is radiation from the sun that strikes the outer surface of a house wall and is absorbed causing the wall to heat up. This heat flows from the outer wall to the inner wall through conduction and is then eradiated again through the air spaces in the building to other surfaces. Radiation is the dominant method of heat transfer in a building accounting for 65-85 percent of all heat transfer through the walls, ceilings, attics and floors.  

Insulation to resist the flow of radiation uses aluminum foil to reflect back the infra-red rays so they do not penetrate into the building or exit the building in winter. Aluminum can reflect up to 97 percent of radiation that strikes it. Traditional fiberglass insulation has no effect on radiant heat transfer. Estimates are between 80 and 90 percent of the radiant heat striking fiberglass will pass right through it. Duct insulation composed of aluminum foil, has proven to be the best radiant heat barrier. Prodex Total duct insulation - 13/64 inch (5mm closed cell polyethylene foam covered on both sides with .0012 inch (0.03mm) aluminum foil facing.

Recommended Duct Insulation Levels

R-value is the measured resistance of one inch of insulation material to conductive and convective heat transfer. Most building codes specify that ducts running through unheated crawlspaces, attics, basements, or garages must be insulated to a minimum of R-4. Optimum insulation levels vary depending on your climate and type of energy used for heating or cooling.

When insulating heating ducts in an unconditioned space, any water pipes in this same space must be insulated as well. In situations where there are un-insulated duct and un-insulated pipes in the same area, heat escaping from the ducts may be helping to keep the pipes from freezing. For this reason, the water pipes could freeze and burst if air ducts are insulated and water pipes remain un-insulated.

The following table, supplied by the US Department of Energy, shows the duct insulation R-values recommended by climate and location. Many states, like the Energy Trust of Oregon, recommend always insulating to the maximum cost effective R-value - in their case R-11.  

Cost-Effective Duct Insulation R-Valuesa

Climate Type of Heating Systemsb R-values for Unconditioned Attic R-values for Unconditioned Basement/Crawlspace
Warm - cooling and minimal heating requirements
(i.e., FL, HI, coastal/inland CA, southeast TX, southern LA, AR, MS, AL, GA)
Gas/oil, electric resistance, or heat pump R-4 to R-8 none to R-4
Mixed - moderate heating and cooling requirements
(i.e., VA, WV, KY, MO, NE, OK, OR, WA, ID; southern IN, KS, NM, AZ; northern LA, AR, MS, AL, GA; inland CA; western NV)
Gas/oil, electric resistance, or heat pump R-4 to R-8 R-2 to R-8
Cold - (i.e., PA; NY; New England; northern Midwest; Great Lakes area; mountainous areas: CO, WY, UT, etc.) Gas/oil, electric resistance, or heat pump R-6 to R-11 R-2 to R-11

a. Adapted from Modera et al., "Impacts of Residential Duct Insulation on HVAC Energy Use and Life Cycle Cost to Consumers," ASHRAE Transactions (#AT-96-13-4)
b. Insulation is also effective at reducing cooling bills. These levels assume that you have electric air conditioning.

According to the U.S. Department of Energy Home Energy Saver web site, insulating ducts in the typical American home costs about $250. Duct insulation will pay for itself in energy savings in about two and a half years, and continue to save energy in all subsequent years.

Prodex Total Versus Fiberglass batt in Ducts

At least some insulation is required for ducts that run within the conditioned space of floors, walls and ceilings to ensure that the conditioned air is delivered at the required temperature and also to prevent condensation on the outside of the duct walls. Ducts within conditioned spaces will experience only minor conductive losses and gains as they are only exposed to indoor air temperatures. However, these ducts often require some insulation to prevent condensation on duct walls which can cause oxidation, corrosion, mold and mildew damage inside floor or ceiling cavities.

Condensation occurs when warm air strikes a cold surface such as a duct carrying cooled air from a central air conditioner. Warm air can carry more moisture than cold air. So when warm, moisture laden air comes in contact with the cold metal surface of the duct, the air will cool. Any excess moisture that the cooler air can no longer hold will condense into droplets. Once the water vapor becomes actual water, it not only oxidized the metal, but has the potential to drip and cause rot, mold and fungus growth that will degrade the surrounding building materials. Prodex Total, properly installed, will act as a vapor barrier and prevent condensation on the duct surfaces.

One of the biggest drawbacks of using fiberglass batt insulation is its vulnerability to moisture.  When ducts experience condensation, moisture collects in the fiberglass, causing it to pack and lose its insulating value. In addition, during the wrapping process of insulation, the fiberglass is pulled tight around corners causing packing which interferes with the ability of the fiberglass to achieve full insulating R-value. Fiberglass batt insulation must be carefully installed and kept dry to maintain its stated R-value. The other major drawback of using fiberglass batt insulation is that it has no effect on radiant heat transfer. The difficulty of maintaining loft during installation, protecting against moisture, and preventing breathable fibers from coming into contact with workers have lead experts to recommend alternatives, such as Prodex Total to be used as duct wrap.

Prodex Total is installed with spacers so that the insulation installed sits away from the duct surface creating an air space both to reflect radiant energy and prevent moisture buildup. Prodex Total will also not compress on corners or have its R-value affected by moisture or humidity.

Benefits of using Prodex Total Duct Insulation

Additional benefits of Prodex Total:

  • Performance unaffected by moisture or humidity
  • Prevents 97% of radiant heat keeping radiant energy away from the duct.
  • Reflects escaping radiant heat back inside the duct.
  • Prevents condensation as a vapor barrier 
  • Provides protection from moisture
  • Reduces noises and vibrations
  • Safer for workers to install than fiberglass -there are no fibers to breath or cause skin or eye irritation.
  • Nontoxic and non-carcinogenic - does not irritate the skin, eyes, or throat and contains no substances which will out-gas
  • Increases energy efficiency of heating and cooling equipment by reducing the equipment work load.
  • Seals around nails (no leaks)
  • Elastic
  • Keeps its thickness over time (doesn't collapse)
  • Does not promote mold or mildew
  • Does not provide for nesting of rodents, birds or insects
  • Washable 

Installating Duct Insulation

ductwork installation method Proper installation calls for first sealing all points in the duct run. Then an insulation jacket is wrapped around both the ducts and the plenum (or furnace bonnet).

Duct joints and any other leaks are sealed with mastic that is brushed and dried. Mastic seals joints to protect against both air loss and drop in velocity. The speed of air travel through the ducts determines how well it will hold its temperature. Duct joints that are properly sealed will carry air at a maximum capacity. Foil tape can be used to seal joints prior to installing the insulation.

Click for pricing or to order Prodex Total Insulation

Click for duct insulation installation instructions 

  1. Measure perimeter of ducts.
  2. Cut 2 inch strips out of the insulation rolls equal to the length of perimeter.
  3. Attach the insulation strips to the ducts with double sided tape or glue (Super Metal Sealant) every 16 inches.
  4. Attach the insulation to the strips with double sided tape or glue (Super Metal Sealant).
  5. Tape seams with reflective tape.
  6. If applying a 2nd layer of insulation, repeat steps 1 - 5. 

United States Environmental Protection Agency,
“Duct Insulation”,
Air and Radiation (6202J), EPA 430-F-97-028, December 2000.

U.S. Department of Energy,
“A Consumer`s Guide to Energy Efficiency and Renewable Energy: Duct insulation”,
September 2005.

“Insulating Ducts for Efficiency”,, 2001

Bonneville Power Administration,
“Insulating Pipes and Ducts”,
April 2004

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