Design considerations for window performance
- Climate and location»
- Orientation»
- Window area»
- Shading»
- Select window type»
- Ensure proper installation»
Select window type
A variety of window technologies can improve window energy efficiency, including gas fills, low-E coatings, and high-performance frame options. How these technologies affect a window's energy performance depends on the sum of all parts. This is where whole window energy ratings help, accounting for the combined effect of glazing, spacers and frame. The only reliable way to determine whole-window energy properties are the ratings certified by the National Fenestration Rating Council (NFRC). In most jurisdictions across the United States, building energy codes require that windows bear the NFRC label so that the code compliance of their energy ratings can be verified.
NFRC energy ratings
The energy ratings included on the NFRC label are the U-factor, Solar Heat Gain Coefficient (SHGC), Visible Light Transmittance (VT) and, optionally, Air Leakage (AL) and Condensation Resistance (CR).
What energy performance to aim for?
Building energy code: At a minimum, windows energy ratings need to comply with the requirements of the code applicable to the homes jurisdiction. - ENERGY STAR®: Not all jurisdictions have adopted up-to-date energy codes yet, but the ENERGY STAR label helps ensure that windows have above-average energy performance. In most locations, ENERGY STAR criteria exceed energy code requirements. ENERGY STAR criteria and recommended window properties by climate zone are shown here.
- Window Selection Tool: This tool offers a quick comparison of how different window types impact typical home energy bills in a specific climate. The Window Selection Tool also shows which EWC members manufacture products within the different window categories.
- House-specific simulation: To model the conditions of the specific house and take into account the impact of shading, orientation, or glazing area, use more detailed simulation software like RESFEN.
Ensure proper HVAC sizing
Lower heating and cooling demand from efficient windows may allow you to offset part of the window cost upfront by opting for smaller HVAC equipment. Taking advantage of this HVAC downsizing potential not only makes efficient windows even more attractive, it also prevents equipment oversizing. Right-sizing HVAC equipment helps avoid inefficient stop-and-go cycles that are detrimental to humidity control and occupant comfort.
Ensure proper installation
Once you have chosen energy-efficient windows for the new home, make sure that they perform as expected and ensure proper installation.
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