A thermal camera may reveal missing insulation, a thermal bridge or an air leak. But an image of a wall taken just after a sunny afternoon may mostly show stored solar heat. The conditions of the inspection matter as much as detector resolution.
Look for a sustained temperature difference
Building-envelope defects are easier to see when indoor and outdoor temperatures have differed meaningfully for several hours. During the heating season, you will usually look for unusually cold areas inside and unusual warmth outside. There is no universal temperature threshold: the building, moisture and the defect itself affect the image. FLIR gives a 6°C (about 11°F) indoor–outdoor difference as one workable example, not a guarantee that every defect will be visible.
Keep the heating reasonably steady before inspecting. Record the indoor and outdoor temperature and the time of day so a follow-up image can be interpreted in context.
Avoid direct sun and note wind
Sunlit masonry can retain heat after shade or sunset; a warm patch then need not be a heat leak. An early morning or overcast inspection reduces this confounding effect. Changing wind can move or conceal the pattern of an air leak. Recent rain matters too: evaporation and moisture affect surface temperature.
Start inside, then check the explanation
- Scan a complete wall to see the pattern before zooming in on one spot.
- Compare similar windows and surfaces under similar conditions.
- Take a visible-light photograph and record the material, distance and emissivity setting.
- Check the cause: air leakage, missing insulation, condensation and nearby heating require different remedies.
A cold ceiling corner may point to a thermal bridge, but the camera records apparent surface radiation. It does not directly see insulation behind a wall or prove where moisture came from. Read what a thermal camera can actually show during a leak investigation for a related example.
Which camera works for a home inspection?
A phone attachment can be suitable for a first look at nearby surfaces when its native resolution and field of view put enough pixels on the target. At greater distances or for repeatable reporting, also examine focus, sensitivity, measurement corrections and exported file data. Set your working distance in the building inspection selector or use the target-size calculator before comparing models.
Practical rule: plan for stable temperature contrast, limit direct sun, document conditions and corroborate an anomaly before drawing a conclusion.
Sources and scope
- FLIR, things to know before a building energy audit: contrast, sun and wind.
- FLIR, thermal imaging for building efficiency: example conditions and limits.
Documentary guide; The Thermogram did not conduct a hands-on test for this article. Sources checked September 24, 2026.