You can pay a company to conduct a thorough energy audit to find out where energy is escaping from your house. Or your local utility might do one for you at no charge. But before you call anyone, conduct your own audit online with the help of the Energy Efficiency and Renewable Energy Network of the Department of Energy. You certainly won't be wowed by the look of the site, but it will help you calculate the energy efficiency of your house and provide solid information to help you reduce heating and cooling bills. There's also a section on hiring an energy auditor.