When to turn the heating back on, and the free step that comes first
There is no official date for turning the heating back on. The useful marker is not the calendar but the indoor temperature: you switch it on when the home no longer holds 19 °C on its own, which usually happens between mid-October and early November depending on the region and the insulation.
Before switching on, one free action changes the equation: close the curtains before dusk. A curtain holds back the heat already in the room, and according to ADEME, windows account for 10 to 15% of a home's heat loss.
The right question is not the date, it is the temperature
French energy regulations set the average heating temperature in dwellings at 19 °C. That is the marker to use, and it beats any date: two homes on the same street do not have the same thermal mass, the same exposure or the same insulation.
In practice the rule fits in one sentence: turn the heating on the day your living room stays below 19 °C at the end of the day, despite the afternoon sun. For most French households, that falls between mid-October and the first days of November.
Three things to do before switching on
Each one is free, and each one pushes back the date when heating becomes necessary.
| Action | What it changes |
|---|---|
| Open wide during the day, close before dusk | By day, the sun heats for free. In the evening, the curtain holds that heat instead of letting it escape through the glass. Closed too late, it traps air that is already cold. |
| Check that the curtain overlaps the frame | A panel that stops at the glass lets air pass along the sides. That is the leak double glazing does not fix. |
| Air the room briefly and fully, not slowly and partly | Five to ten minutes wide open renews the air without cooling the walls. A window left ajar for an hour does the opposite. |
Why the curtain works before the radiator
A curtain produces no heat: it slows its escape. That is why it goes up before the season rather than during it. Installed in late November, it does not recover what was lost in October, it only limits what is left to lose.
The Union des Fabricants de Menuiseries adds a useful caveat to the ADEME estimate: the 10 to 15% does not account for air leakage around windows already installed. Yet that circulating air is exactly what a dense curtain works on.
What thickness actually changes
Below 300 gsm, the thermal effect stays marginal: the fabric dresses the window, it does not insulate it. The difference comes from density and the number of layers.
| Type of curtain | Weight | Thermal effect |
|---|---|---|
| Sheer or light-filtering | 265 gsm | No thermal effect. It filters light and protects daytime privacy. |
| Single-layer blackout | 310 gsm | Blocks light completely, but does nothing thermal or acoustic. |
| Thermal blackout, three layers | 620 gsm | Up to 7 °C difference at the glass, and 22 dB attenuated. |
The full reasoning is in our guide which curtain weight to choose, and the comparison of types in our thermal curtain comparison.
The useful calendar
September is the month when these steps are prepared, not the month the heating starts. Our autumn curtains page gathers what gets settled before the first cold spell, and the winter curtains page takes over from mid-October.
Frequently asked questions
Is there an official date for turning the heating on?
No. No date is set for an individual home. What is regulated is the temperature: French energy law uses 19 °C on average in dwellings. In an apartment block, the start date for central heating is decided by the building manager, often around 15 October.
Is turning the heating down at night worthwhile?
Yes in a well-insulated home, where the temperature falls slowly. In a home that loses heat quickly, the morning restart can cost more than the night saved. A closed curtain is precisely what reduces that overnight loss.
Should curtains stay closed during the day in winter?
No, not on a sunlit window: solar gain is free heat. Open wide by day, close before dusk. On a north-facing window that never gets direct sun, keeping the curtain closed is defensible.
Does a thermal curtain replace a portable heater?
No. It produces no heat at all. It acts on how fast the room loses its own, which pushes back the moment heating becomes necessary without replacing it.
To fit your windows before the first cold spell: our made-to-measure thermal curtains, made to your dimensions in 620 gsm across three layers.
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