Windows are thermal holes. An average home may lose 30% of its heat or air-conditioning energy through its windows. Energy efficient windows save money each and every month. There are even some cases where new windows in strategic locations can be net energy gainers. The payback period for selecting energy efficient units ranges from two to ten years. In new construction, the higher initial cost can be offset because you will need a smaller less expansive heating and cooling system. More durable windows will also cost less in the long haul because of lower maintenance and replacement costs. Plus you will be more comfortable the whole time you live with them.