Find out more about purchasing windows and doors on DOE's Office of Building Technology and State Programs Web site. In the summer, especially in southern climates, solar gains through windows can dramatically increase building energy use for cooling. Window treatments to reduce solar gains can pay off rapidly, but depends on the treatment method used. The installation of more efficient replacement windows is often too expensive an option to pay for itself through avoided energy costs. In such buildings, the replacement of clear windows may be cost-justified since large solar gains through windows can account for 25 percent or more of the cooling load.
Air sealing to minimize air infiltration can also be very costly.
It is important to find and concentrate air sealing efforts on the major sources of air leakage into a building, since they can easily account for a large percentage of the air infiltration. Because mechanical ventilation systems for schools are designed to bring in outdoor air, many buildings operate under a slight positive pressure and air leakage into the building is not a concern. If mechanical ventilation is not used, air infiltration will likely be uncontrolled and can result in significantly higher energy use. Where high humidities are present, uncontrolled air infiltration can be an even greater concern because moisture can move through building cavities, where it can be detrimental to the building's structural components and materials. Smaller school buildings may use unconditioned attic space as the return air path to the heating or cooling system.