Among the most efficient ways to reduce energy bills and make your house temperatures more comfortable is an energy audit using thermal imaging, or thermography. Starting at about $500, a home energy audit can not only spot a lot of problems by simple examination, but can also show you precisely where invisible energy wasters are by using a thermal imaging camera. Imagine a picture showing in color exactly where your house is leaking heat!

Thermography cameras extend human vision into the invisible, far infrared spectrum of light -- light that is emitted by warm objects. Everything radiates this invisible light; warmer objects and areas show up in contrast to surrounding areas that are even slightly cooler. Mosquitos use this method to locate warm bodies; doctors use thermal scans to locate areas where blood flow is higher, and therefore warmer, such as tumors or infections. You can even see the warm spot where the dog has been sitting on the sofa while you're away, despite his wagging pretense of innocence. The producers of the Ghost Hunters TV show would have you believe that spirits are visible with thermal images, as they often show video with fleeting infrared images. The images you see on that show often have FLIR printed in the corner, which is the name of manufacturer of the most popular cameras. (The name FLIR comes from Forward Looking Infrared Radar, a military application of thermal imaging.)

Thermal imaging helps pinpoint specific energy flaws in your home, so you can focus your home improvement dollar where it will do the most good. For instance, earlier work on your house may have dislodged, compacted, or removed insulation, and thermography will show these areas as clearly as an x-ray shows bones. These infrared images will show damp areas, too, because moisture changes the insulating properties of any porous material. Older houses may lack insulation altogether. A more common energy culprit is air leaks, especially around doors, windows, and furnace or air-conditioning ducts.  Dangerous or wasteful electrical hot spots also can show up, such as a bad electrical connection, an overworked motor, or a failing circuit breaker.

Because the biggest energy offender is often air leaks, your energy auditor will probably also employ a blower fan door to create a slight vacuum in your house. This door is a plastic fabric rectangle that fits in an exterior doorway, has a fan in it, and special electronic controls to ensure a precise vacuum. This vacuum sucks air from outside, or from the ducts that carry warm or cool air in your house, through unseen cracks. This air warms or cools the surrounding materials, and the thermal camera then reveals these areas. The inspector provides interpretation of the importance of the leaks.

Increasingly, energy auditors are certified in their trade, with tests to make sure that the auditor makes proper use of the equipment, does not incorrectly interpret camera or blower door results, and provides useful reports. Certifying agencies include The Residential Energy Services Network (RESNET), the Building Performance Institute, and the Association of Energy Engineers (AEE). An energy audit, besides being a useful tool for home improvement, can be part of a house inspection before buying, or can be a sales tool for a seller.