Quick answer: The testo 868 records apparent surface-temperature patterns. To compare images meaningfully, document emissivity, reflected radiation, palette scale and distance; a thermogram cannot directly detect water behind a wall.
What makes the testo 868 different
The testo 868 is a handheld thermal imager for identifying apparent surface-temperature patterns in building inspection. Thermal colour differences are not a direct moisture map. For related guidance, see 871 Thermal Camera Setup: Emissivity and Building Inspection Guide.
Prepare and carry out the measurement
- Check model generation, lens and firmware manual, and allow camera/environment stabilization as specified.
- Set emissivity and reflected-temperature assumptions appropriate to the inspected surface; avoid polished targets.
- Capture overview and close-up images with repeatable distance, focus and temperature scale.
- Corroborate a suspected anomaly using suitable temperature, humidity or moisture tests and document conditions.
Model-specific use and interpretation
Allow the camera to adapt to measurement conditions, set emissivity and reflected temperature appropriately, and acquire a visible/context image of each wall. Use the same palette and temperature scale for comparisons. For a closely related model, see the testo 872 setup guide.
The colours on a thermal image represent a selected rendering of radiometric temperatures. Colour contrast alone is not a defect category. Apparent surface temperature patterns can be due to material, geometry, reflection, sunlight or airflow.
An edge-of-wall cold strip may suggest a thermal bridge, air leakage or weather effects; corroborate using air/surface temperature and moisture investigations. For the mechanism behind cold, moisture-prone wall areas, see the guide to wall condensation causes.
Worked example (hypothetical)
Hypothetical wall comparison: two painted surfaces show apparent temperatures of 14 °C and 18 °C under matched emissivity/scale settings. The 4 °C contrast identifies an area for investigation; it does not prove failed insulation or concealed dampness.
Interpretation limits and safe follow-up
- Shiny surfaces may reflect a hot or cold object that is not the target itself.
- A thermal bridge, air movement or damp material can show overlapping patterns; corroborate with appropriate independent measurements.
- Electrical and high-temperature assets must be examined from approved safe positions by competent personnel.
- If inspecting an older model, verify its own manual instead of adopting instructions from later 868s, 871s or 872s models.
A repeatable building-envelope survey
With the testo 868, select comparable indoor and outdoor temperature conditions for a building scan. Check emissivity on painted versus shiny surfaces, avoid direct sun and record the location and scale of each view. Use the visual image to identify the wall segment, then corroborate a suspicious cold line with a surface measurement or moisture inspection. The picture alone does not identify hidden dampness. For the corroborating moisture check, see the guide to building moisture inspection.
Interpretation: Comparing a corner at 13 °C with a central wall at 17 °C is useful only when both apparent temperatures were acquired with consistent emissivity and palette scale.
Limits and safety
Follow the exact instrument manual and the equipment manufacturer’s acceptance criteria. The example is not field evidence, a legal limit or a commissioning target. Work on energized electrical equipment, combustion systems, charged refrigerant circuits or hot surfaces requires qualified personnel and the site’s approved protective procedures.