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Efficient Windows Collaborative

Measuring Performance: ENERGY STAR® Windows

Windows that have the ENERGY STAR designation will be labeled showing the zones in which it is qualified.

Energy Star   Energy Star Zones

Northern Zone Required Properties (mostly heating)
U-factor Solar Heat Gain Coefficient (SHGC) Visible Transmittance (VT) Air Leakage (AL)
Windows: U≤0.27
Windows: U=0.28
Windows: U=0.29
Windows: U=0.30
Skylights: U≤0.50

EWC Recommendation: For superior energy performance, use windows with a U-factor of 0.25 or less. If passive solar strategies are to be used, there may be a trade-off with a high SHGC value. If this is the case, make sure proper passive design strategies are implemented (thermal mass, proper shading) to prevent overheating during the summer seasons.
Windows: SHGC=Any
Windows: SHGC≥0.32
Windows: SHGC≥0.37
Windows: SHGC≥0.42
Skylights: SHGC=Any

EWC Recommendation: If air conditioning is not a concern, look for a high SHGC (0.35-0.60) so that winter solar heat gains can offset a portion of the heating energy need. If cooling is a significant concern and no shading is available, select windows with a SHGC less than 0.32. Select skylights with a SHGC of 0.40 or less.
Windows: VT=No Requirement
Skylights: VT=No Requirement

EWC Recommendation: Select windows with a higher VT to maximize daylight and view.
Windows: AL≤0.30
Skylights: AL≤0.30

EWC Recommendation: Select windows with an AL of 0.30 or less.

North/Central Zone Required Properties (heating & cooling)
U-factor Solar Heat Gain Coefficient (SHGC) Visible Transmittance (VT) Air Leakage (AL)
Windows: U≤0.30
Skylights: U≤0.53

EWC Recommendation: The larger your heating bill, the more important a low U-factor becomes. For superior energy performance, use windows with a U-factor of 0.25 or less.
Windows: SHGC≤0.40
Skylights: SHGC≤0.35

EWC Recommendation: A low SHGC value reduces summer cooling demand, but also reduces free winter solar heat gain. If you have significant air conditioning costs or summer overheating problems, look for SHGC values of 0.25 or less. If you have moderate air conditioning requirements, select windows with a SHGC of 0.40 or less.
Windows: VT=No Requirement
Skylights: VT=No Requirement

EWC Recommendation: Select windows with a higher VT to maximize daylight and view.
Windows: AL≤0.30
Skylights: AL≤0.30

EWC Recommendation: Select windows with an AL of 0.30 or less.

South/Central Zone Required Properties (heating & cooling)
U-factor Solar Heat Gain Coefficient (SHGC) Visible Transmittance (VT) Air Leakage (AL)
Windows: U≤0.30
Skylights: U≤0.53

EWC Recommendation: The larger your heating bill, the more important a low U-factor becomes. 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 during warm seasons.
Windows: SHGC≤0.25
Skylights: SHGC≤0.28

EWC Recommendation: Select windows with a SHGC of 0.25 or less.
Windows: VT=No Requirement
Skylights: VT=No Requirement

EWC Recommendation: Select windows with a higher VT to maximize daylight and view.
Windows: AL≤0.30
Skylights: AL≤0.30

EWC Recommendation: Select windows with an AL of 0.30 or less.

Southern Zone Required Properties (mostly cooling)
U-factor Solar Heat Gain Coefficient (SHGC) Visible Transmittance (VT) Air Leakage (AL)
Windows: U≤0.40
Skylights: U≤0.60

EWC Recommendation: 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.
Windows: SHGC≤0.25
Skylights: SHGC≤0.28

EWC Recommendation: A low SHGC is the most important window property in warm climates. For superior energy performance, use windows with a SHGC of 0.25 or less.
Windows: VT=No Requirement
Skylights: VT=No Requirement

EWC Recommendation: Select windows with a higher VT to maximize daylight and view.
Windows: AL≤0.30
Skylights: AL≤0.30

EWC Recommendation: 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

 

 

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