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. This guide shows how to plan a visit, interpret patterns cautiously and decide when a repeat scan is worthwhile.
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.
Must you wait until winter?
Winter is convenient when a house is heated and the outside is colder. Summer may also work when air conditioning creates a sustained indoor–outdoor contrast, though the direction of the patterns changes. The calendar alone cannot determine whether the scan will be useful. If the temperature gap has narrowed or the heating has only just started, wait for more stable conditions before drawing conclusions.
Roofing, masonry and floors retain heat from earlier hours. A sunlit slab does not immediately return to the same state as a shaded wall. Good conditions for one surface do not necessarily make every part of the building comparable.
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.
Make two deliberate passes
Start indoors with wall and ceiling corners, window surrounds, shutter boxes and floor junctions. Keep the palette and temperature scale consistent between comparable images; an automatically rescaled palette can make similar surfaces appear dramatically different. Then inspect outside where access, distance and conditions allow. Exterior images add context, but different materials and sun exposure make a direct color-to-color comparison unreliable.
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. ISO 6781-1 describes complementary methods that may be needed to verify an anomaly. Read what a thermal camera can actually show during a leak investigation for a related example.
Read the pattern without assuming the cause
Repeated cold lines at framing members may suggest thermal bridging. A diffuse streak near a window may suggest moving air. Evaporation from moisture can also cool a surface. These are hypotheses to test, not diagnoses. Compare with a similar wall facing the same way, look for visible evidence and use an appropriate air-leak or moisture test where the cause matters.
Glass, shiny metal and other reflective surfaces can mirror radiation from the surroundings. The displayed color may then give a misleading impression of the target's temperature. Pair each thermal image with a visible photograph, a precise location and the conditions of capture.
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.
Frequently asked questions
Can I inspect after rain?
Sometimes, but wet surfaces and drying produce their own temperature patterns. For insulation work, wait until you can separate that weather effect from the anomaly you are looking for.
Is one thermal image enough to plan repairs?
No. It highlights an area to investigate. The cause and remedy may require another observation or a site diagnosis. Save the original image and capture conditions before asking a specialist to investigate.
Sources and scope
- ISO 6781-1:2023, building thermography: framework for examining heat, air and moisture irregularities.
- US Department of Energy, building-envelope research report: sun exposure and limits of interpreting anomalies.
- Testo, emission and reflection in thermography: reflective surfaces.
- FLIR, building energy inspections: example temperature contrast.
Documentary guide; The Thermogram did not conduct a hands-on test for this article. Illustrations are not actual measurements. Sources checked September 24, 2026.