Click this link to watch a few short videos on energy use in an existing home.
This book will provide you with some ideas of areas where energy can be wasted in an existing home.
Simply put, insulation's main function is to keep heat where you want it to stay, in the summer you want to keep the heat out and in the winter you want to keep it in the home. The ability of insulation to perform that function is directly related to how well it is installed. Click on the 'play' button to watch the insulation effectiveness video and learn a few things that will help you learn more about insulation.