Felt temperature vs air: how surfaces affect comfort in renovation

Understanding felt temperature to better target comfort

Air temperature and radiation: why your customers feel cold at 20°C

At 20°C, your customers can still feel cold if the surfaces stay at 16 or 17°C. The body then loses heat through radiation. What really matters is the so-called operative temperature, a blend of air temperature and average surface temperature.

The role of surfaces: ceiling, walls, glazing and thermal bridges

Ceiling, walls and glazing pull the sensation down as soon as they're colder than the air. Thermal bridges create very localised "cold" zones. In practice, you gain comfort by treating thermal bridges and the envelope before pushing the heating up.

Signs on site: draughts, cold surfaces, zones of discomfort

On site, spot signs of discomfort right from the visit.

• Draughts at the foot of windows.
• Cold surfaces at thermal bridges and shutter boxes.
• Cooler zones near glazing, possible condensation.

An infrared thermometer helps prioritise airtightness fixes, insulation and junction work to restore proper comfort.

Cold surfaces: the mechanisms that degrade day-to-day comfort

Radiation toward surfaces: the "cold wall" effect explained simply

When a wall is colder than the air, your body "gives" it heat through radiation. As a result, you can have 20°C on the thermometer and still feel a cold wall. It's often compensated for by turning up the heating, without gaining comfort, especially near façades and glazing.

Surface temperature and condensation: impacts on comfort and the health of the home

If the indoor surface drops too low, moisture in the air can condense. A cold surface then encourages persistent humidity, mould and odours. The result: less comfort and a home that's heavier to live in. Continuous insulation, thermal bridge treatment and properly adjusted ventilation break this cycle.

Thermal inertia and time lag: when a surface stores or loses heat

A heavy, well-insulated surface stores heat and releases it slowly. Without insulation, inertia works against you. The mass "pumps" gains and sends them back outside. Thermal time lag helps smooth out variations and keep comfort more stable.

Measuring and validating comfort on site in 2026

Useful measurements: surface temperature, humidity, air speed, thermal camera

On site, comfort is proven with a few simple measurements. Record the surface temperature of walls and glazing (infrared thermometer), humidity (ideally in a stable zone), and air speed near windows to get objective data on draughts. The thermal camera helps visualise thermal bridges and insulation defects, provided you aim for a sufficient indoor-outdoor temperature gap and avoid direct sunlight.

Assessing surfaces before works: key points of an energy audit in 2026

Before proposing a solution, back up your on-site observations with the audit. Identify cold surfaces, the condition of the insulation, airtightness, and above all the ventilation-humidity balance. In 2026, the regulatory energy audit is also an expected benchmark for homes classed E, F or G at the time of sale.

Translating results into customer benefits: less low felt temperature, more comfort

Turn the figures into concrete benefits. A surface at 15°C means a sensation of cold even with 20°C air. Fewer cold surfaces and air leaks means more comfort, less condensation, and steadier heat, room by room.

Surface works: the solutions that genuinely improve felt temperature

Wall insulation: internal vs external, continuity and thermal bridge treatment

External wall insulation is often the most effective for smoothing out temperatures, since it keeps the wall's thermal inertia on the inside and limits thermal bridges to floor junctions, partition walls, and window reveals. Internal wall insulation remains relevant in occupied housing or co-owned buildings. In both cases, aim for continuity. Treat insulation returns, wall-floor junctions and penetrations.

Windows and airtightness: limiting discomfort near glazing

Cold near a window comes as much from a cold glazed surface as from air leaks. A well-installed replacement, with draught-proofing and airtight junctions, quickly changes comfort. Also think about shutter boxes and sills. And keep ventilation properly set, otherwise damp air creeps in.

Ceilings, ground floors and lofts: the surfaces often forgotten

Lofts and roof slopes often give the best ratio of comfort gain to budget. On a ground floor, insulate under the slab or from underneath depending on access. Don't forget the loft hatch, edges and fascias, to avoid the "icy floor" effect. Well-treated ground floors make the difference.

Properly adjusting heating and ventilation to stabilise comfort after renovation

Emitters and controls: lowering the setpoint without losing comfort thanks to warmer surfaces

After insulation, walls and ceilings are warmer. As a result, you can often lower the setpoint by 1°C while keeping the same comfort. Adjust room by room with thermostatic heads, a well-placed room sensor and, on a heat pump, a heating curve set to avoid short cycling. Also think about balancing radiators or underfloor heating.

Ventilation: avoiding dry air and draught sensations (settings and maintenance)

An overly "pulled" mechanical ventilation system creates a draught sensation and can dry out the atmosphere. Check that air inlets aren't blocked, clean the vents, and change filters if you have heat-recovery ventilation. The goal is well-dosed renewal, with humidity around 40 to 60%.

Job handover: checking comfort and explaining felt temperature to the customer

At handover, check temperature, humidity and flow rates. Demonstrate the settings and explain "felt temperature" as it relates to radiation from surfaces. 19°C in a renovated house can feel more pleasant than before. Hand over a simple sheet, for lasting settings.