ENERGY STAR® Windows
The Department of Energy (DOE) and the Environmental Protection
Agency (EPA) have developed an ENERGY STAR® designation for products
meeting certain energy performance criteria.
Since energy efficient
performance of windows, doors, and skylights varies by climate, product
recommendations are given for four U.S. climate zones. For making
comparisons among ENERGY STAR®
products, use the NFRC label or the NFRC Certified Products Directory.
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Incentives and rebates for energy-efficient windows and other efficient products.
.pdf file»
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Northern Zone Recommended Window Properties (mostly heating)
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U-factor |
Solar Heat Gain Coefficient (SHGC) |
Visible Transmittance (VT) |
Air Leakage (AL) |
Windows: U=0.35 or less
Skylights: U=0.60 or less (20°)
Skylights: U=0.45 or less (90°)
If air
conditioning loads are minimal, windows with U-factors as high as 0.40 are also energy-efficient if
the Solar Heat Gain Coefficient is 0.50 or higher.
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Windows: SHGC=No Requirement
Skylights: SHGC=No Requirement
To reduce heating, select the highest SHGC you can find (usually 0.30-0.60
for the U-factor ranges required in colder climates) so that winter solar gains
can offset a portion of the heating energy need. If cooling is a significant
concern, select windows with a SHGC less than 0.55. Select skylights with a SHGC of 0.55 or less.
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Windows: VT=No Requirement
Skylights: VT=No Requirement
Select windows with a higher VT to maximize daylight and view.
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Windows: AL=No Requirement
Skylights: AL=No Requirement
Select windows with an AL of 0.30 or less. |
North/Central Zone Recommended Window Properties
(heating & cooling)
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U-factor |
Solar Heat Gain Coefficient (SHGC) |
Visible Transmittance (VT) |
Air Leakage (AL) |
Windows: U=0.40 or less
Skylights: U=0.60 or less (20°)
Skylights: U=0.45 or less (90°)
The larger your heating bill, the more important a low U-factor becomes.
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Windows: SHGC=0.55 or less
Skylights: SHGC=0.40 or less
If you have significant air conditioning
costs or summer overheating problems, look for SHGC values of 0.40 or less. If
you have moderate air conditioning requirements, select windows with a SHGC of
0.55 or less. While windows with lower SHGC values reduce summer cooling and
overheating, they also reduce free winter solar heat gain.
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Windows: VT=No Requirement
Skylights: VT=No Requirement
Select windows with a higher VT to maximize daylight and view.
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Windows: AL=No Requirement
Skylights: AL=No Requirement
Select windows with an AL of 0.30 or less. |
South/Central Zone Recommended Window Properties
(heating & cooling)
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U-factor |
Solar Heat Gain Coefficient (SHGC) |
Visible Transmittance (VT) |
Air Leakage (AL) |
Windows: U=0.40 or less
Skylights: U=0.60 or less (20°)
Skylights: U=0.45 or less (90°)
A low U-factor is useful during cold days
when heating is needed. A low U-factor is also helpful during hot days when it is
important to keep the heat out, but it is less important than SHGC in warm
climates. The larger your heating bill, the more important a low U-factor becomes.
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Windows: SHGC=0.40 or less
Skylights: SHGC=0.40 or less
Select windows with a SHGC of
0.40 or less. A low SHGC is the most important window
property in warm climates.
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Windows: VT=No Requirement
Skylights: VT=No Requirement
Select windows with a higher VT to maximize daylight and view.
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Windows: AL=No Requirement
Skylights: AL=No Requirement
Select windows with an AL of 0.30 or less. |
Southern Zone Recommended Window Properties (mostly cooling)
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U-factor |
Solar Heat Gain Coefficient (SHGC) |
Visible Transmittance (VT) |
Air Leakage (AL) |
Windows: U=0.65 or less
Skylights: U=0.75 or less (20°)
Skylights: U=0.75 or less (90°)
A low U-factor is useful during cold days
when heating is needed. A low U-factor is also helpful during hot days when it is
important to keep the heat out, but it is less important than SHGC in warm
climates. Select windows with a U-factor lower than 0.65 and preferably lower
than 0.60.
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Windows: SHGC=0.40 or less
Skylights: SHGC=0.40 or less
Select windows with a SHGC of
less than 0.40. A low SHGC is the most important window
property in warm climates.
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Windows: VT=No Requirement
Skylights: VT=No Requirement
Select windows with a higher VT to maximize daylight and view.
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Windows: AL=No Requirement
Skylights: AL=No Requirement
Select windows with an AL of 0.30 or less. |
U=U-factor in Btu/hr-sf-°F
SHGC=Solar Heat Gain Coefficient in fraction of incident solar angle
VT=Visible Transmittance in fraction of incident visible radiation
AL=Air Leakage in cfm/sf
(20°) U-factor qualification criteria based on 2001 NFRC simulation and certification procedures that rate skylights at a 20-degree angle. Although reported U-factor is higher than RES97 rated products, energy performance at the Energy Star minimum qualifying level is equivalent.
(90°) NFRC certification using the 1997 NFRC procedures for residential windows (RES97) that rated skylights at a 90-degree angle. Skylights rated under this procedure may be present in the marketplace until March 31, 2008. NFRC labels for products using this procedure state: "RES97 rated at 90 degrees."
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