High Performance Windows
United States
Air and Radiation
EPA 430-F-97-028
Environmental Protection
(6202J)
December 2000
Agency
H IGH-P ERFORMANCE W INDOWS
BUILDING ENVELOPE IMPROVEMENT
Windows typically comprise 10 to 25 percent of the
The materials and design of the frame also influence
exterior wall area of new homes. Research studies
thermal performance. Low conductance materials,
report that windows in heating-dominated climates
such as wood, vinyl, and fiberglass, perform better
account for up to 25 percent of a typical house’s heating
than high conductance materials such as aluminum.
The U.S. Environmental Protection
Agency’s ENERGY STAR® Program
load and that in cooling-dominated climates, windows
Look for “thermal breaks” where aluminum frames
promotes the use of high-efficiency
account for up to 50 percent of the cooling load.
are used in heating-dominated climates to avoid
technologies and equipment. ENERGY
condensation. And finally, insulated frames perform
STAR labeled homes use at least 30%
less energy than homes built to meet
In recent years, many technological advances have
better than uninsulated.
the national Model Energy Code
been made that significantly enhance the thermal
while maintaining or improving
indoor air quality. These fact sheets
performance of windows. As shown in Figure 1,
Air tightness is another important consideration.
are designed to help consumers
these technologies include improved framing
Windows are now being tested and rated for air
learn more about the energy-
materials, low-emissivity and solar control coatings,
tightness. A rating of 0.2 cfm/ft (cubic feet per
efficient improvements to their
ENERGY STAR labeled homes.
low-conductance gas fills, improved thermal breaks
minute of air leakage per linear foot of window edge)
and edge spacers, and better edge sealing
or lower is considered good. The best windows
techniques. These technologies can be used
have a rating of 0.1 cfm/ft or lower.
independently or in combination, but must be
selected based on climate to optimize performance.
An effective building envelope is a key element for
an energy-efficient home. ENERGY STAR labeled
Windows can improve the thermal performance of
homes are often constructed with high-performance
homes by minimizing heat loss in heating-dominated
windows that can improve the effectiveness of the
climates and by minimizing solar heat gain in
building envelope and improve comfort.
cooling-dominated climates. Thus windows with
lower U-factors or higher R-values perform better in
heating-dominated climates and windows with lower
F IGURE 2 : THERMAL PERFORMANCE
solar heat gain coefficients (SHGC) perform better in
CHARACTERISTICS OF VARIOUS
cooling-dominated climates (see Figure 2). SHGC is
WINDOW SYSTEMS
a measure of the amount of solar energy that a
Air
glazing material allows to pass.
Window System
U-factor
Leakage
Description
[R-value]
SHGC
(cfm/ft)
Triple glazing with 2
0.15
0.37
0.08
F IGURE 1 : H IGH-P ERFORMANCE W INDOW
Low-E coatings and
[6.2]
argon gas fill in an
insulated vinyl frame.
Double glazing with a
0.33 to
0.55 to
0.15
New frame materials
Low-E coating and argon
0.30
0.44
and designs
gas fill in a wood or
[3.0 to 3.3]
Low-emissivity and/or
vinyl frame.
solar control coatings
Double glazing in a wood
0.49
0.58
0.56
Low conductance gas fills
or vinyl frame.
[2.0]
Insulating spacer
Single glazing in an
1.30
0.79
0.98
between glazings
aluminum frame with no
[0.77]
thermal break.
from Residential Windows, John Carmody, et. al., Norton & Company, 1996.
H IGH-P ERFORMANCE W INDOWS
BUILDING ENVELOPE IMPROVEMENT
R ESOURCES
B ENEFITS
The Consumer Guide to Home
High-performance windows can provide many
which results in lower utility bills, making homes
Energy Savings, (Wilson and
benefits including:
less expensive to operate.
Morrill) 5th Edition, 1996,
available from the American
Council for an Energy Efficient
Improved comfort. High-performance windows
Reduced obsolescence. Based on recent trends for
Economy at 510-549-9914
reduce conductive heat losses and gains resulting in
improved efficiency, high-performance windows are
Homemade Money (Heede and
warmer interior surfaces during the winter and
expected to become standard practice for the
the staff of RMI), 1995, available
cooler interior surfaces during the summer. In
building industry. Since it is both difficult and costly
from the Rocky Mountain Institute
homes, approximately 40 percent of our physical
to replace windows after a house is built, it is best to
at 970-927-3851
comfort is due to the radiant heat exchange between
install high-performance products during the original
The following fact sheets are
our bodies and the surrounding interior surfaces.
construction. ENERGY STAR labeled homes
available by calling the
Thus, high-performance windows improve comfort
constructed with high-performance windows are,
Environmental Protection Agency’s
toll-free E
by reducing this radiant heat exchange. In addition,
therefore, expected to be less vulnerable to
NERGY STAR Hotline at
1-888-STAR-YES (1-888-782-7937):
improved frames reduce drafts and provide more
obsolescence.
Increased Insulation and Air
consistent temperatures throughout the house.
Sealing
Fewer condensation problems. High-performance
Energy Efficiency in Windows
Quieter home. High-performance windows often
windows stay warmer in the winter resulting in drier
fact sheet available from the
utilize multiple glazing and insulated frames. These
windows with fewer condensation-related problems.
Energy Efficiency and Renewable
Energy Clearinghouse (EREC),
features reduce unwanted noise from the outside.
Condensation can stain fabrics, lead to mold and
P.O. Box 3048, Merrifield, VA 22116,
mildew build-up, and in cold climates cause damage
1-800-DOE-EREC (1-800-363-3732)
Increased quality. High-performance windows are
due to the freeze/thaw cycle.
often constructed with better quality materials that
can result in stronger, easier to operate, and longer
Reduced wear on home furnishings. Low-E
lasting windows. As a result of these improvements,
coatings can block up to 98 percent of the ultraviolet
manufacturers frequently offer extended warranties
radiation emitted by the sun. This radiation causes
on these products.
curtains, window treatments, carpeting, and
furniture to fade and wear faster.
Improved indoor air quality. High-performance
windows often have air tightness ratings of
Improved resale position. High-performance
0.2 cfm/ft or less which reduce the amount of
windows can provide the many impressive benefits
unconditioned air leakage into a house. This air
listed above resulting in a more comfortable, quieter,
leakage can bring in dirt, dust, and other impurities
and higher quality home with lower utility bills and
that can negatively affect indoor air quality.
fewer condensation and fading problems. These
benefits can translate into higher resale value.
Lower utility bills. High-performance windows are
better insulated and more air-tight. These features
reduce energy consumption for heating and cooling
