Trees can reduce demand for air conditioning to cool buildings by shading residences and lowering summertime air temperatures. During winter, trees can reduce heating needs by lowering wind speeds and thereby reducing infiltration of cold air. On the otherhand, winter shade from improperly located trees can increase heating requirements. Projections from computer simulations indicate that 100 million mature trees in U.S. cities (3 trees for every other single family home) could reduce energy use for heating and cooling by 30 billion kWh and reduce carbon dioxide emissions by as much as 9 million tons per year. This energy analysis is part of a larger study that quantifies costs and benefits of proposed tree plantings in 12 U.S. cities. While energy savings is an important benefit from community forests, other benefits (e.g., air quality improvement, reduced stormwater runoff, increased property values) can have equal or greater value. Tree planting, care, and other costs (e.g., water-sewer line repair, green waste disposal, litigation/liability, program administration) from the cost-benefit study can be used to help estimate costs associated with a tree planting program for demand-side management. Data from this energy analysis should be of direct value to local utilities, urban foresters, planners, landscape designers, and non-profit tree planting groups.