My windows leak. My door has a draft. And many more energy saps are just waiting to be discovered. I know I am due for an "energy audit." I've heard that most homes have the equivalent of a large open window 24/7. That's energy literally going out the window.
Energy auditors can detect where houses are losing energy. These guys come armed with high-tech tools such as a thermographic camera that detects heat loss. The camera can detect if heat is going through your insulation because the insulation is not adequate.
Some leaks we might not feel are easy to find with the naked eye. Did you know spiders are your friends? Spiders like to build webs where there is a draft. Just look for the spider webs and you will find the leaks in your house.
Energy efficiency probably wasn't a major concern when most houses are built. Even newer houses have leaks. Air sealing is a great investment in keeping your house warm.
For more information on how to improve your home's energy efficiency, check out this NYT video link featuring Tom Zeller Jr., the editor of the Green Inc. blog. In this video Zeller hires specialists from Green Treen Energy to track cown the spots in his house where energy is lost.