Cities Selected to Calculate Energy Efficiency

• Window energy efficiency was determined by computer simulation using RESFEN 5.0 computer program, developed by Lawrence Berkeley National Laboratory, Berkeley, CA

• Window related energy consumption of existing windows were compared to replacement windows using the same home model

• The change in window related energy consumption was used to calculate the improvement in window energy efficiency

• Calculations were conducted using the default parameters for each location as established in RESFEN 5.0

• The construction selected was an existing one-story frame construction

• The HVAC system type selected was a gas furnace and electric AC for all locations

• The floor area assumed was 2,000 square feet

• The window area assumed was 15% of the floor space (300 square feet of window area) with equal distribution of windows on each side of the home

• The calculations did not include any assumed energy efficiency improvements for improved air infiltration

• The existing window selected to compare against in all locations was a wood or vinyl single-pane window with clear glass (U = .84, SHGC = .63)

• Replacement windows selected to compare against in all locations for Pella® products included:

  • 350 series products analyzed

    • 350 series double hung window with 1-1/4" Advanced Low-E Triple-pane IG with argon with 3 mm glass (U = 0.19, SHGC = 0.24)

    • 350 series casement window with 1-1/4" Advanced Low-E Triple-pane IG with argon with 3 mm glass (U = 0.17, SHGC = 0.20)

    • 350 series fixed window with 1-1/4" Advanced Low-E Triple-pane IG with argon with 3 mm glass (U = 0.15, SHGC = 0.27)

  • Designer Series® products analyzed

    • Designer Series double hung window with 5/8" Advanced Low-E IG with 2.5 mm glass with argon with 2.5 mm Low-E HGP (U = 0.24, SHGC = 0.24)

    • Designer Series casement window with 5/8" Advanced Low-E IG with argon with 2.5 mm Low-E HGP (U = 0.26, SHGC = 0.22)

    • Designer Series fixed casement window with 5/8" Advanced Low-E IG with argon with 2.5 mm Low-E HGP (U = 0.23, SHGC = 0.25)

• The window energy efficiency comparison was made for 94 cities. The 94 cities are the same cities ENERGY STAR posted city energy savings estimates for on their website as of 11/2/12. The cities are a sampling of all 50 states except Hawaii, consistent with the approach by ENERGY STAR. The table below lists the cities analyzed.

Performance Information

U-Factor, Solar Heat Gain Coefficient (SHGC), and Visible Light Transmittance (VLT) are certified by the National Fenestration Rating Council (NFRC). Manufacturer stipulates that these ratings conform to applicable NFRC procedures for determining whole product performance. NFRC ratings are determined for a fixed set of environmental conditions and a specific product size. NFRC does not recommend any products and does not warrant the suitability of any product for any specific use. 

Design Pressure (DP), Performance Class, and Performance Grade (PG) are certified by a third party organization, in many cases the Window and Door Manufacturers Association (WDMA). The certification requires the performance of at least one product of the product line to be tested in accordance with the applicable performance standards and verified by an independent party. The certification indicates that the product(s) of the product line passed the applicable tests. The certification does not apply to mulled and/or product combinations unless noted. Actual product results will vary and change over the product’s life.

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