Introduction
A handheld thermometer or thermal camera may show a cold patch on a wall, a warm line near a ceiling or a sudden temperature difference beside a doorway. Such patterns can look striking in a dark building, but temperature is governed by heat transfer, materials, airflow and measurement technique.
Thermal engineering offers a structured way to investigate these observations. The key is to understand what the instrument actually measures and how building surfaces exchange heat.
Three modes of heat transfer
Conduction transfers thermal energy through a material. A metal frame, concrete beam or poorly insulated junction can conduct heat differently from the surrounding wall.
Convection transfers heat through moving fluids such as air. Draughts, stack effect, ventilation and pressure differences can create local temperature patterns.
Radiation transfers energy through electromagnetic waves. Infrared cameras detect radiation in a wavelength band and estimate surface temperature using assumptions about emissivity and reflected surroundings.
These processes occur together in real buildings.
What is a thermal bridge?
A thermal bridge is a part of a building envelope where heat flows more readily than through adjacent insulated areas. Examples include concrete balconies, metal fixings, window frames and junctions between walls and floors. Thermal bridges can produce surface-temperature differences and, under some conditions, contribute to condensation risk.
A cold patch is not automatically a thermal bridge. It may reflect airflow, moisture, a different surface material, a recent change in heating or a measurement artefact.
Understanding infrared cameras
An infrared camera does not directly measure the temperature inside a wall. It detects infrared radiation from the surface and converts it to an apparent temperature using settings and assumptions.
Important factors include:
- Emissivity: how effectively a surface emits infrared radiation.
- Reflected apparent temperature: radiation reflected from nearby objects can influence the reading.
- Distance and focus: affect spatial detail and measurement reliability.
- Viewing angle: can change readings, especially on reflective surfaces.
- Environmental conditions: wind, sunlight, heating and recent occupancy can alter surface temperatures.
Shiny metal is particularly difficult to measure accurately with many thermal cameras because of low emissivity and reflected radiation.
AERM field protocol
Equipment
- Infrared camera with documented specifications
- Contact thermometer for surface verification
- Air-temperature and relative-humidity logger
- Anemometer where airflow is relevant
- Measuring tape and site sketch
- Camera for recording instrument position and surface context
Procedure
- Record indoor and outdoor conditions, recent weather and heating or cooling status.
- Allow instruments to stabilise according to manufacturer guidance.
- Photograph the surface in visible light as well as infrared.
- Record emissivity and reflected-temperature settings.
- Capture images from repeatable distances and angles.
- Verify important surface readings with a suitable contact thermometer.
- Repeat measurements after a documented interval.
- Note drafts, open windows, dampness, direct sunlight and nearby heat sources.
Interpretation
A thermal image is a map of apparent surface temperature, not a photograph of hidden energy or a direct view through walls. Use it to identify areas for further inspection. If the concern involves dampness, insulation failure or structural performance, seek a qualified building professional.
Common errors
- Comparing surfaces with different emissivity settings
- Treating a single image as a stable baseline
- Ignoring reflections from heaters, people or windows
- Assuming a cold patch indicates a cold object behind the wall
- Using low-resolution consumer devices beyond their capabilities
- Failing to record the camera's scale and measurement settings
Conclusion
Thermal patterns can reveal useful information about building performance, but they require careful interpretation. Conduction, convection, radiation and material properties can produce temperature differences that appear unusual without being unexplained. Repeatable imaging, contact verification and environmental logs help convert an interesting image into a defensible observation.
AERM Core Principle: No anomaly is considered paranormal until environmental, psychological, technical, and scientific explanations have been systematically evaluated.
References and further reading
- ISO 6781-1. Performance of buildings — Detection of heat, air and moisture irregularities in buildings by infrared methods.
- ASTM E1933. Standard Practice for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers.
- ASTM C1060. Standard Practice for Thermographic Inspection of Insulation Installations in Envelope Cavities of Frame Buildings.
- FLIR, technical resources on emissivity and infrared thermography.
- Incropera, F. P. et al. Fundamentals of Heat and Mass Transfer. Wiley.
About AERM
AERM uses environmental measurements as testable evidence. Thermal imaging is documented with instrument settings, repeat measurements and clear statements about what the camera cannot see.
Educational and safety disclaimer
This article is educational and is not a building-energy audit or structural assessment. Do not touch exposed electrical equipment or enter unsafe areas to obtain thermal images. Consult qualified building and electrical professionals where defects are suspected.