http://hes.lbl.gov/

The Home Energy Saver is designed to help
consumers identify the best ways to save energy in their homes, and
find the resources to make the savings happen.  The project is sponsored by the U.S. Department
of Energy (DOE), as part of the national ENERGY STAR Program for
improving energy efficiency in homes, with previous support from the
U.S. Environmental Protection Agency (EPA), the US Department of
Housing and Urban Development's PATH program, and the California
Energy Commission's Public Interest Energy Research (PIER) program.

The
Home Energy Saver computes a home's energy use on-line. Users can
estimate how much energy and money can be saved and how much emissions
can be reduced by implementing energy-efficiency improvements. All end
uses (heating, cooling, major appliances, lighting, and miscellaneous
uses) are included. A detailed description of underlaying calculation
methods and data is provided in a series of specials reports.