Energy auditors may also use thermography infrared scanning
to detect thermal defects and air leakage in building
envelopes. Thermography measures surface temperatures by using
infrared video and still cameras. These tools "see"
light that is in the heat spectrum.
Images on the video or film record the temperature variations
of the buildings skin, ranging from white for warm regions
to black for cooler areas. The resulting images help the auditor
determine whether insulation is needed. They also serve as a
quality control tool, to ensure that insulation has been installed
A thermographic inspection is either an interior or exterior
survey. The auditor decides which method would give the best
results under certain weather conditions.
Interior scans are more common, because warm air escaping from
a building does not always move through the walls in a straight
line. Heat loss detected in one area of the outside wall might
originate at some other location on the inside of the wall.
Also, it is harder to detect temperature differences on the
outside surface of the building during windy weather. Because
of this, interior surveys are generally more accurate, as they
benefit from reduced air movement. Thermographic scans are also
commonly used with the blower door is running. The blower
door helps exaggerate air leaking through defects in the building
shell. Such air leaks appear as black streaks in the infrared
cameras view finder.
Most energy audits take from four to eight hours and cost between
$300 and $500. Any retrofit work would of course cost additional