Infrared thermal imaging: detect heat leaks

Why thermal imaging is a useful diagnostic on your jobs

What an infrared camera really reveals (and what it doesn't show)

Thermal imaging turns temperature differences into an image. On a job, you can quickly spot abnormally cold or hot zones on surfaces. It's an excellent detection tool, but it only "sees" surface temperatures. A reliable reading also depends on conditions. A sufficient temperature gap, no direct sun, no rain, no strong wind, and suitable settings.

The most common defects spotted: thermal bridges, air infiltration, missing insulation

In practice, thermal imaging helps target weak points before demolition, or verify after works. You often identify recurring defects:

• thermal bridges at floors, window reveals, wall-roof junctions
• parasitic air inlets around windows, shutter boxes, hatches, sockets
• missing, settled or poorly installed insulation, especially on roof slopes and lofts

Thermal imaging vs other diagnostic methods: when to favour it

Choose it when you need to move fast and visualise something to decide. To quantify air leaks, an air leakage test remains more suitable. If moisture is suspected, cross-check with humidity readings and inspection. Thermal imaging is the right moment to steer the insulation and airtightness work package, then document your corrections.

When to carry out infrared thermal imaging in 2026 for reliable results

Weather conditions and key moments: heating running, temperature gap, humidity

For reliable thermal imaging, aim for a cold period with stable heating. Ideally, keep doors and windows closed and look for an indoor/outdoor differential of at least 10°C. Avoid direct sun, recent rain and strong wind, which mask defects. Humidity and wet surfaces also skew the reading, since evaporation cools surfaces down.

Before works, during, after: timing the diagnosis to the right stage of the job

Before works, the thermal image is used to prioritise work items. During the job, check right after the insulation is fitted or airtightness work is done, while it's still accessible. After the works, redo a thermal survey under similar conditions to verify insulation continuity and spot anything missed, without waiting for finishes.

Special cases: exterior renovation, lofts, ground floors, windows

In exterior renovation, the best time is before render or cladding, to correct thermal bridges. For lofts, work early in the morning or at night, with the roof not in direct sun. For ground floors, favour winter, especially over a crawl space. For windows, measure at night, to avoid solar gains and condensation.

How to prepare and run a thermal imaging survey without wasting time

Field checklist: access, safety, basic settings, shooting

To move quickly, a successful thermal survey is prepared before the camera is even switched on. Think safety and access.

• Clear access, authorisations, lighting, zones to inspect marked on a plan.
• Cordoning off, PPE, stable ladders, no shooting through glass.
• Basic settings, emissivity, distance, focus, temperature range.
• Shooting, an overview shot then details, same angle as much as possible.

Common mistakes to avoid: reflections, sun, strong wind, shiny surfaces

Track down reflections. Avoid direct sun, rain and strong wind, which cool surfaces and blur the reading. On shiny surfaces, work at an oblique angle, or place a small temporary matte marker.

Note-taking and referencing: linking images, zones and observed symptoms

Ensure traceability. Number the images, link them to a room and a zone, height, orientation, surface type. Note the observed symptom, thermal bridge, insulation defect, air infiltration, moisture. If possible, also take a regular photo of the same frame.

Interpreting a thermal survey: turning images into concrete actions

Reading a thermal image: scale, hot/cold spots, suspicious zones

In thermal imaging, colour alone isn't enough. First look at the temperature scale and the contrast setting. A very hot spot around a junction can signal an air leak or an insulation defect. A cold zone around the edges can reveal a thermal bridge. Watch out for reflections on metal or glazing. They skew the reading. Temperature scale first and foremost.

Cross-checking with the building diagnosis: ventilation, airtightness, humidity

An image alone doesn't settle the question. Cross-check it with a site visit, existing ventilation, air inlets and service penetrations. Diffuse cold patches, especially in corners, can indicate humidity and condensation risk. For a reliable shot, you need a sufficient temperature gap between indoors and outdoors, with no direct sun or strong wind.

Prioritising interventions: fixing leaks before adding insulation

Before thickening the insulation, fix the leaks. Draught-proof windows, shutter boxes, hatches and floor-wall junctions. Then adjust ventilation. A more airtight envelope, without healthy air, traps moisture. Once airtightness defects are reduced, you can aim for continuous insulation and limit thermal bridges. To go further, also see continuous insulation as an approach for durably treating the envelope. A winning order of works.

Making the most of thermal imaging with your customers and in your job files

Simple arguments to explain the diagnosis and reassure the customer

Thermal imaging is a thermal photo of the home. It shows where heat escapes, without breaking or drilling anything. You turn a feeling into visible facts. The result: less doubt and works that are more readily accepted, especially on insulation and airtightness.

Report format: photos, annotations, recommendations, quote

In your report, keep 3 to 5 telling images, with a simple caption and an annotation on the relevant zone. Add an operational recommendation and the associated quote. A before/after comparison, even on one specific point, provides visual proof that makes deciding easier.

RGE, grants and energy audit in 2026: where thermal imaging provides evidence

In 2026, grants mainly require technical supporting documents and invoices. Thermal imaging generally isn't mandatory, but it strengthens your applications. It supports an energy audit, documents thermal bridges or installation defects, and helps demonstrate that the proposed works are consistent with RGE requirements and CEE operation sheets.