RESFEN is used for calculating the heating and cooling energy use of windows in residential buildings. Using a computer program such as RESFEN to compare the performance of window and skylight options allows you to customize the calculation by adding heating and cooling costs for your specific climate, house design options, and utility rates. The user defines the house with a series of selections from a menu: location, heating and cooling system type and efficiency, utility rates, floor area, window area, window orientation, interior/exterior shading, etc. A specific window or set of windows for each orientation is selected and specified by their U-factor, SHGC, and air leakage rate. The program then calculates the annual heating and cooling energy use and cost as well as peak heating and cooling loads. It is designed so that different window types can be placed on different orientations.

NREL’s BEopt

The BEoptâ„¢ (Building Energy Optimization) software provides capabilities to evaluate residential building designs and identify cost-optimal efficiency packages at various levels of whole-house energy savings along the path to zero net energy.

Looking for windows for a new home?

Use the Window Selection Tool to compare annual energy performance for windows in new construction.

Looking for replacement windows?

Use the Window Selection Tool to compare annual energy performance for replacement windows.