Building Energy Software Tools
Formerly hosted by US Dept. of Energy    


Reviews 0

RESFEN calculates the heating and cooling energy use and associated costs as well as the peak heating and cooling demand for specific window products. Users define a problem by specifying the house type (single story or two story), geographic location, orientation, electricity and gas cost, and building configuration details (such as wall type, floor type, and HVAC systems). Window options are defined by specifying the window's size, shading, and thermal properties, i.e., U-factor, Solar Heat Gain Coefficient, and air leakage rate.

RESFEN calculates the energy and cost implications of the windows compared to insulated walls. The relative energy and cost impacts of two different windows can be compared against each other.

Expertise Required: 

Minimal knowledge about windows.


Window manufacturers, glass manufacturers, building contractors, architects, engineers, and homeowners who are interested in predicting the energy performance of residential window systems.


Geographic location; electricity and gas cost; infiltration; internal load levels; HVAC; wall and floor type; as well as window size, type, U-value, shading coefficient.

RESFEN has a set of "Libraries" where information is stored and input. Each library has a List view, where all the records (rows) in the library can be viewed, and a Detail view, where all the data (or fields) in each record can be viewed.

House Library

Locations Library: RESFEN has a Locations Library which can be used to create new locations that reference specific weather data and insulation packages. In the default database that is installed, there are 240 locations for the United States, as well as four for Canada. There are also other databases (for Canada, Chile and China) with more locations defined.

Window Library: RESFEN has a Window Library that allows data for specific windows to be imported from the WINDOW5 program. A default set of Berkeley Lab WINDOW data is included, and other data can be imported as needed or provided by manufacturers or other sources.

Packages Library: RESFEN has a Packages Library, which allows the user to create new insulation packages that can be associated with a Location to create customized modeling situations.

Results Library: RESFEN has a Results Library, which allows the user to view results from multiple runs, as well as export those results to comma separated text files that can be imported into a spreadsheet program.

Electric Rates Library: RESFEN has an Electric Rates Library, which allows the user to add new rates or change existing rates. The default library contains one rate for each US state, based on data from the Energy Information Administration (

Gas Rates Library: RESFEN has a Gas Rates Library, which allows the user to add new rates or change existing rates. The default library contains one rate for each US state, based on data from the Energy Information Administration.


Annual energy use and cost for heating and cooling; peak load increments due to the windows. Results given for two discrete sets of window orientations (north, east, south, west) or (northwest, southeast, southwest, northwest).

Can also calculate incremental changes due to obstructions, overhangs, and interior shades.


Easy to use, immediate, accurate.

United States
Major Capabilities: 
Whole Building Energy Simulation
Parametrics and Optimization
Weather Data and Climate Analysis
Building Type: 
Subsystem Level
Help and Support: 
Free Email Support
Last Software Update: 
30 June 2010
Last Entry Update: 
20 September 2018
Add to compare