Sustainable Spaces is a San Francisco based home performance retrofitting contractor that helps improve the health, comfort and energy efficiency of homes. Their home performance specialists will examine both the building envelope, such as windows and insulation, and the major home systems like the furnace and A/C units. They will then work with in house contractors to make energy efficiency updates as needed. These retrofits save homeowners an average of 40% on their energy bills and that adds up to 745,300 kWh and 149,060 Therms saved by Sustainable Spaces in 2008.