How to Use a Thermal Camera the Right Way

A thermal camera is one of the highest leverage tools in the inspection trades, but the workflow is not intuitive. The same camera in two operators' hands produces wildly different reports. The difference is technique, not the camera. Here is how to use a thermal camera so the images are useful and the findings are defensible.

Step 1: Set Emissivity

Emissivity is how much infrared a surface emits compared to a perfect blackbody. Most painted surfaces, drywall and wood read at 0.95. Polished metal reads at 0.05 to 0.30 and reflects the surroundings instead of showing its own temperature. The wrong emissivity gives readings that are off by 50+ degrees.

Most cameras default to 0.95 which works for most building inspection work. For shiny metal, set emissivity to 0.30 or apply a temporary matte paint or tape patch.

Step 2: Set Reflected Apparent Temperature (RAT)

RAT compensates for the temperature of nearby objects reflected onto the surface. Indoors, set RAT to room temperature (typically 20 to 22 degrees Celsius). For outdoor scans on a sunny day, ambient air temperature is fine.

Step 3: Pick the Right Palette

• Iron / Hot Iron. Default for most building science. Easy to interpret.
• Rainbow. High contrast for subtle anomalies but harder to interpret in reports.
• Greyscale. Best for documentation when colour is distracting.
• White Hot / Black Hot. Quick scans where you only care about hot or cold spots.

Step 4: Focus

Out of focus thermal images give blurry temperature readings. Use the camera's focus ring (auto focus on premium models, manual on entry level). The temperature reading sharpens with the image.

Step 5: Get Differential

Thermal imaging works best when there is a temperature difference between the inside and outside. Cold winter day or hot summer day are ideal. A mild spring day with 70 degrees inside and 65 outside gives little contrast and most defects do not appear.

Step 6: Capture Both Visible and Thermal

Most modern cameras have an MSX overlay that combines edge detail from the visible camera with the thermal image. This makes labels, vents and serial plates readable in the thermal capture. Always save both the thermal and the visible image of the same scene.

Step 7: Annotate

On the image, drop a measurement spot on the area of interest. Note the temperature delta vs the surroundings. Add a text annotation describing what the operator was looking at and why.

Common Mistakes

• Inspecting in mild weather (no temperature differential)
• Default emissivity on shiny metal (reads ambient instead of metal)
• Out of focus images (blurry temperature)
• Not capturing the visible reference image
• Reporting findings without a confirmation tool reading

Pair With Other Tools

A thermal finding always needs confirmation. For moisture: pair with a moisture meter. For electrical: pair with a clamp meter. For inside walls: pair with a borescope.

Browse thermal imaging cameras from FLIR and Extech sized for residential inspection through industrial work.

The thermal camera is a confirmatory tool, not a diagnostic one. Used with the right emissivity, the right temperature differential and a confirmation reading, it is the most efficient inspection tool available. Used poorly, it produces images that no one can interpret.