What an occupant calls felt temperature has a name in calculation, the operative temperature, and it comes down in good approximation to the average of the air temperature and the mean surface temperature. A living room at 20 °C of air surrounded by walls at 16 °C therefore sits at an operative 18 °C, and that is the value the body perceives. The consequence for pricing is direct: insulating a wall so it rises from 16 to 19 °C gains 1.5 °C of operative temperature without touching the thermostat. Regulation reasons in averages too, with the French energy code capping the mean heating temperature across all rooms of a dwelling at 19 °C outside periods of non-occupancy.
Understanding felt temperature to better target comfort
Air temperature and radiation: why your customers feel cold at 20°C
At 20 °C of air, the occupant feels cold if the surfaces stay at 16 or 17 °C, because the body loses heat by radiation towards colder surfaces. The quantity that describes this is the operative temperature, the average of the air temperature and the mean surface temperature.
| Situation | Air T | Mean surface T | Operative T |
|---|---|---|---|
| Uninsulated wall, single glazing | 21 °C | 15 °C | 18 °C |
| Uninsulated wall, double glazing | 20 °C | 16.5 °C | 18.3 °C |
| Internally insulated wall | 20 °C | 18.5 °C | 19.3 °C |
| Externally insulated wall, bridges treated | 19 °C | 18.5 °C | 18.8 °C |
The last row is the commercial argument for the job: the air setpoint drops from 21 to 19 °C for a higher felt comfort. It is also the only honest way to promise a saving without promising the client a worse life.
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 the technical survey, record surface temperatures with an infrared thermometer rather than trusting the feel, and note the gap against the ambient air in the same place as the rest of the survey, on the phone where Argile records the home and the project measure by measure. A gap above 3 °C on an ordinary wall flags a fix worth making. The points to check first:
- 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.
