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Duct Insulation
Duct Insulation
In Arizona, most air conditioning system ductwork is installed in the attic where
temperatures can soar above 140 degrees in the summer. Cool air flowing through
ducts is about 55 degrees, so if your ducts arent properly insulated, you could be
air conditioning your attic!
Poor duct insulation can cause these problems:
Warm rooms and uncomfortable hot spots in the house.
The cooling system works extra hard to keep rooms comfortable.
Moisture and condensation on metal ducts can cause rust and provide a
breeding ground for mold and mildew.
If possible, visibly inspect your duct insulation. Check to see if your duct insulation
needs repair and look for thin spots or areas with no insulation.
Insulating Ductwork
If you suspect your ducts need insulation or the duct
insulation you have needs to be repaired, contact an APS
Qualified Contractor. A contractor can help you deter-
mine if its practical to add insulation to your ducts.
An APS Qualified Contractor can also help you decide if
duct repairs and insulation can be done at a reasonable
cost. If so, youll save money on energy bills and improve
the overall comfort of your home.
Check for Air Leaks
Have a qualified contractor check your ducts for leaks. Air leaks waste energy,
cause comfort problems and make your system work harder to keep your home
cool. If you can see excessive dirt build-up on your duct insulation, you probably
have air leaks. Insulation doesnt block leaks in your ductwork it merely covers
them from view.
If youre having your ducts insulated, be sure to have all joints and fittings sealed
with mastic duct sealant to eliminate leaks. See the Energy Answers fact sheet on
Reducing Duct Leakage for more information.
Higher R-Values Equal Greater Efficiency
An insulations resistance to heat flow is measured as R-value. The higher the
R-value, the more effective the insulation. The R-value of duct insulation depends
on its thickness and density, and how much the insulation is compressed when
installed. Compression reduces its R-value.
ENERGY
ANSWERS The two most common types of duct insulation systems are:
Blanket duct wrap for metal ducts and plenums APS recommends a
minimum level of R-6.
Insulated flexible duct (the insulation is included as part of the duct with
R-values of 4, 6 and 8). APS recommends at least an R-6.
The chart shows the insulating values of different types of duct wrap insulation.
Proper Installation Determines
Efficiency and Performance
Quality of installation has a big influence on
the performance of duct insulation.
Be sure that the insulation is securely
fastened to the duct, and that all seams
are sealed with duct tape.
The insulation should fit snugly against
the surface of the duct wall and com-
pletely cover all exposed surfaces.
Insulation must not be compressed too
tightly during installation or its insulat-
ing value will be reduced.
If the outside cover of the insulation is
accidentally torn or punctured during
installation, it should be sealed with
duct tape.
How Much Can Uninsulated Ductwork Cost You Each Year in
Heating and Cooling Costs?
The energy cost associated with uninsulated ductwork depends on where the
ductwork is installed, how hot the surrounding air is and how long the air condi-
tioning system runs.
For a typical Phoenix area home with a 3-ton air conditioning unit, you could be
paying as much as $1 to $3 per year in extra energy cost for each foot of uninsulated
duct in your attic. A typical Phoenix area home has about 110 feet of ductwork. If
uninsulated, the ducts can waste about $150 to $250 in cooling costs each year.
For More Information or a Referral to an
APS Qualified Contractor
For more information on home energy efficiency, or a referral to an APS Qualified
Contractor, call the APS Energy Answer Line in Phoenix at (602) 371-3636 or
toll-free 1 (888) 890-9730 or visit our web site at www.apsc.com. Be sure to ask for a
contractor who specializes in duct system testing and repair.
Typical R-Values for Duct Wrap Insulation
Density
Thickness
Typical R-Values
Low (0.75 PCF)
1.5
5.0 5.1
2
6.7 6.9
3
10.0 10.3
Medium (1.0 PCF)
1.5
5.6 5.7
2
7.4 7.5
High (1.5 PCF)
1.5
6.0 6.2
2
8.0 8.3
Note: PCF stands for pounds per cubic foot. For a typical
installation, the installed R-value will be about 20% less than
the rated value due to normal compression of the insulation
during installation.
© 1999, Arizona Public Service Company MM-5K-0699-AS