Are you haunted by the spirits of heating seasons past? Are your ghosts all staying toasty while you shiver in a draft? Don’t call Ghost Hunters, call an energy auditor who knows the occult science of thermography.

You may have seen spectral images like the one above on TV or in a science magazine.  They show the surface temperature of whatever is in the picture, using a spectrum of colors instead of numbers to show the range of temperatures. The picture is called a thermographic or thermal image, and requires a special camera. You can use these pictures like a heat-sensitive x-ray of your home’s “envelope” of walls, ceilings, floors and roof. (No, nobody can see you inside, stud, unless maybe you flatten yourself to the wall for 10 minutes. Even then you’ll look at best like Casper the blobby ghost.)

Technical Stuff: Thermographic cameras let humans see the invisible, far infrared spectrum of light -- light that is emitted by warm objects. Everything radiates this invisible light. Warmer objects or areas contrast with surroundings that are even slightly cooler. Mosquitoes use this method to locate warm bodies; doctors use thermal scans to locate areas where blood flow is higher, like 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 Ghost Hunters would have you believe that spirits are visible in thermal images, as the show’s video is replete 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 one of the most popular cameras. (The name FLIR comes from Forward Looking Infrared Radar, a military application of thermal imaging.)

How does this help you? Heat leaks, like air leaks in a tire, can be small but significant. The thermal image shows heat leaks that might be easily fixed but that you might otherwise miss. It shows the temperature in detail across walls, ceilings, doors, windows, heating systems and hot air ductwork, using color to point out differences of less than one degree. The cameras are so sensitive, a thermal image often shows wooden wall studs, because they conduct heat faster than the surrounding insulated areas. If insulation is missing or failing in one section of the wall, that section will stand out as cooler (assuming a cool day outside). If your insulation is good, but a mouse has chewed a hole in it, that will show up. Maybe that’s what’s going on behind the blue spot in the photo below.

Thermal images not only show insulation failures, but also point out where drafts or air leaks occur. Air leaks are the biggies of heat loss in houses, especially older ones, creating mysterious, creepy drafts that are hard to hunt down.  The image will show where cold air is leaking into the house, or where warm air is leaking out of heating duct joints that have lost their seal.

Of course, leaks of warm air out of the house don’t show up well from the inside. Even leaks of cold air into the house may not be visible from the inside, depending on the weather, what windows, vents, or fans are open, and whether or not your heating system is on.

To get all these variables under control and find out just how much and where air is leaking, thermographers often work with a “blower door”. This door is a plastic sheet that temporarily replaces a door to the outside, and is equipped with a fan, sensors, and a sophisticated control unit. This door lets the inspector create a precise vacuum in the house and measure how much air flow results. This will tell the inspector if the house is in general leaky or tightly sealed.  The thermal image then shows where the biggest leaks are. Maybe the builder did not seal well around your wall sockets or ceiling lamps, perhaps the seal is bad on a door or window, or the flap on an exhaust vent is stuck open. This blower door test is important. After all, improving your insulation or heating system is not going to help much if most of your heat is leaking outside or from hot air ducts into an unfinished basement or attic.

Sometimes insulation problems are small, but repeat throughout your house: the builder (or you) may have methodically failed to insulate or seal around recessed lighting, outlets, window frames, floors, exhaust vents, and the like. Thermographic images really shine at finding these. Thermographic images can also show damp wood or insulation – the homeowner’s worst curse, as those areas not only leak heat but cause structural damage by inviting insects, rodents, mold and dry rot. Such areas, perhaps caused by uncontrolled rain flow, leaky basements, clogged gutters or rainpipes, splashing, or too-close shrubbery can otherwise go undetected for years.

Thermographic images are best taken under the right conditions. Optimally, this means thermographing the inside, not the outside of the house, on a cold, still evening. Artwork, books, and furniture need to be removed from the wall. Daytime thermography can be done, but can be complicated by sunlight and shadows, so care is essential.

The images also must be properly set up and interpreted, so the inspector needs training. Issues such as reflections, likely causes, types of materials, sensitivity, and range of temperatures displayed can confuse the analysis, otherwise. The inspector also needs experience in possible causes and typical values. Does the fact that one wall is two degrees cooler than the next mean there is a problem there, or is it just that the outside of the cooler wall is more damp from today’s rain?

Thermography is a great tool, particularly when used with a blower door, but it doesn’t take the place of home inspection (energy auditing) by a knowledgeable person. That’s because there are “big picture” issues, like “will I save more energy adding insulation to the attic, or to the floor joists?” or “Should I put on reflective shingles or install an attic fan to keep heat down?” These issues require estimating where the problem is worst, where it can be most cost-effectively fixed, where replacement with newer technology will make a difference, and what things around the house are likely to fail soon anyway, regardless of their efficiency.

Energy audits can cost from zero dollars to $500 and up, depending on their thoroughness and the expertise of the auditor. Power companies often offer free energy audits, but these rarely involve thermography or blower door analysis. They can be quite helpful nonetheless in evaluating big-picture issues like level of insulation, condition of windows, or refrigerator operating cost. At the very least you’ll get some free compact fluorescent lights (maybe including some hard-to-find ones, like dimmables or three-ways), some coupons and a low-flow shower head out of the visit. Such an audit can be a requirement for getting financial aid or subsidies. In our home, it qualified us for a seven-year, interest-free $15,000 loan for our geothermal system, gave us $150 off a new fridge, and $1500 off additional insulation in the attic.

The pricier audits generally include a detailed written report, giving you quantitative analysis and recommendations. Increasingly, energy auditors are certified in their trade. Some of the certifying agencies are The Residential Energy Services Network (RESNET), the Building Performance Institute, and the Association of Energy Engineers (AEE). A professionally-done audit can will not only help you exorcise (or learn to live with) the invisible forces of evil, but the report and the records of your follow-up may also help you sell your house at a better price.