Home Energy Audits: Thermographic Inspections
Energy auditors may use thermography—or infrared scanning—to detect thermal defects and air and water leakage in building envelopes.
**How they work**
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 structure’s skin, ranging from white for warm regions to black for cooler areas. The resulting images help the auditor determine whether insulation is needed and where it should go. They also serve as a quality control tool, to ensure that existing insulation has been installed correctly.
A thermographic inspection is either an interior or exterior survey. The energy auditor decides which method would give the best results under existing weather conditions.
Interior scans are more common because warm air escaping from a structure does not always move through 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 a structure during windy weather. Because of this difficulty, interior surveys are generally more accurate because they benefit from reduced air movement.
Thermographic scans are also commonly used with a blower door test running. The blower door, which pulls air out of the interior, helps exaggerate air leaking through defects in the structure’s shell. Such air leaks appear as black streaks in the infrared camera’s viewfinder.
In addition to using thermography during an energy audit, you should have a scan done before purchasing a house; even new houses can have defects in their thermal envelopes. You may wish to include a clause in the contract requiring a thermographic scan of the house. Performed by a certified technician, it is usually accurate enough to use as documentation in court proceedings.
The energy auditor may use one of several types of infrared sensing devices in an on-site inspection. A spot radiometer (also called a point radiometer) is the simplest. The auditor pans the area with the device, which measures radiation one spot at a time and notes it.
A thermal line scanner shows radiant temperature viewed along a line.
The thermogram shows the line scan superimposed over a picture of the panned area. This process shows temperature variations along the line.
The most accurate thermographic inspection device is a thermal imaging camera, which produces a two-dimensional thermal picture of an area showing heat leakage. Spot radiometers and thermal line scanners do not provide the necessary detail for a complete home energy audit. Infrared film used in a conventional camera is not sensitive enough to detect heat loss.
Preparing for a thermographic inspection
To prepare for an interior thermal scan, the homeowner should take steps to ensure an accurate result. This may include moving furniture away from exterior walls and removing drapes.
The most accurate thermographic images usually occur when there is a large temperature difference (at least 20 degrees Fahrenheit between inside and outside air temperatures. In northern states, thermographic scans are generally done in the winter. In southern states, however, scans are usually conducted during warm weather with the air conditioner on.
Information courtesy of EERE
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