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Methodology for ENERGY STAR Savings Estimates for Windows

Savings estimates are based on energy calculations performed by Lawrence Berkeley National Laboratory (LBNL) using RESFEN 5.0 for typical homes in 96 U.S. cities. RESFEN is the standard software program used for calculating the impact of windows on heating and cooling costs for residential new construction or existing housing stock. The "typical home" is defined as the traditional construction assemblies for the location. A mix of homes (one- and two-story homes with either a slab, crawlspace, or basement foundation) were modeled. The one-story home is 1,700 square feet and the two-story home is 2,600 square feet. The homes have 15 percent of their floor space as the amount of windows and are equally distributed in the ordinal directions. Heating and cooling systems for each model include either natural gas heat and electric air conditioning or an electric heat pump.

Representative windows were selected from the RESFEN window library. For ENERGY STAR qualified windows, types were selected for each city based on the city's ENERGY STAR climate zone. For single pane windows, an aluminum frame model was selected for Florida and a wood/vinyl frame model was selected for cities elsewhere. For double-pane windows, clear-glass windows were selected from the library with wood/vinyl framing for cities in the Northern, North-Central, and South-Central climate zones and aluminum framing for Florida. Heating and cooling energy savings of the one- and two-story models are averaged together by each space conditioning system. All calculations used EIA 2006 average natural gas prices and 2007 electricity prices.

Regional savings estimates were weighted with the heating equipment type likely for each Census Division or state according to EIA's 2005 Residential Energy Consumption Survey.

Hawaii was excluded from this analysis as RESFEN assumptions applied in the base data set diverge significantly from the norm in Hawaii.

For more information on RESFEN, visit Lawrence Berkeley National Laboratory (LBNL) Exit ENERGY STAR.