Inspectors turn to infrared cameras to spot air leaks that the eye cannot.

After home heating oil prices surged last winter, Meghan Kaiserman decided this fall to get ahead of any price spike and go thermal – that is, she chose to get a thermal-imaging home-energy audit.

So, on a recent chilly morning, Ms. Kaiserman and thermal-energy auditor David Valley walked through her large 1940s ranch-style home, stopping every few steps to examine a color screen on Mr. Valley’s camera. The device scans walls and other surface temperatures in the infrared spectrum – heat energy invisible to the human eye – and displays them as colors. Blue, dark purple, and black indicate cold levels; white, orange, and red represent warm areas. Snapshots of walls become part of a home’s thermal documentary.

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