Infra-red thermography works on the principle that infra-red radiation is emitted by materials, and the intensity of this radiation is proportional to the material's temperature and emissivity.

Thermography is used to study temperature variations over the surfaces of a structure.  Variations in the structure's thermal resistance can, under certain conditions, produce temperature variations on its surfaces.  Leakage of cold (or warm) air through the structure also affects the variation in surface temperature.  This means that heat loss through these insulation defects, and heat loss through thermal bridges and air leaks in a building's enclosing structural components can be located and surveyed.

Investigations have shown that defects found in the thermal insulation and air tightness of buildings cause house heat loss that is about 20-30% more than was expected.  Monitoring energy consumption before and after remedial measures in relatively large complexes of small houses and in multi-dwelling blocks has also demonstrated this.  A cautious assessment would be that effectively testing and checking a builidng's thermal insulation and air tightness can result in a reduction in energy consumption of about 10%.

Research has also shown that increased energy consumption associated with defects is often caused by occupants increasing the indoor temperature by one or a few degrees above normal to compensate for the effect of thermal radiation traveling towards cooled surfaces or a sensation of disturbing air movements in a room.