Cooling off on Saturday: will you have to turn on your heating?

As a general rule, the heating is turned on between October 5 and 20 and turned off around April 15. This varies depending on the region, your accommodation and above all, the weather. With climate change, if we notice that the heating has been turned on frequently after October 15 for the past two decades, it also happens that early periods of great coolness encourage you to turn it back on punctually in September. This may have been the case for you in 2017, which was the coldest September in recent years, and during which the thermal indicator fell to 16.43 ° C, or more than 1.5 ° C below average. Compared to the month of September 2021, which had been the hottest with an indicator of 21.45°C, the notion of extreme climate variability takes on its full meaning.

Reminder on Unified Degree Days (DJU)

The degree day is a value representative of the difference between the average temperature of a day (which is obtained by adding the minimum and maximum temperature then dividing the result by two) and a pre-established temperature threshold (17°C) . Summed over a period, the DJU calculate the heating or cooling needs of a building. This data is calculated every day to establish monthly averages, but also annual ones during the “heating season”, which by convention extends from January to May and from October to December. These results are then compared to the statistics for the period 1991-2020, to define a rigor index.

If this index is greater than 1, this means that the period considered was more rigorous than the average. It will have been less rigorous otherwise. Thus, since 2013, only 3 years have been harsher: 2013, 2016 and 2021 (which had been marked by severe frosts in April, by the coldest month of May since 2000, and by several episodes of cold from January to March and from November to December).

The month of September is not included in these calculations, but it still happens, as in 2017, that cool spells are observed. This was particularly the case during the period from the 15th to the 20th, when temperatures were particularly cool and on average 3 to 4°C lower than normal. These cool periods are therefore not uncommon in September, as will be the case from next weekend. So, what to expect in the next few days?

Lasting boost of freshness

Switching on the heating is recommended when the interior temperature falls below 19°C for several consecutive days, and the thermal indicator (average outside temperature) reaches 17°C. The thermal indicator calculated by our services will drop to 13.9°C from this Saturday and remain between 2 and 3°C below normal at least until Friday September 23, the situation will therefore be conducive to the recovery en route from your boiler.

It is explained by the establishment, at altitude, of a cold current of polar origin preceding a flow from the continental east. This development will lead to a general drop in temperatures during the nights and mornings. Thanks to the sunshine, which is much more present in the south than in the north, the drop will however be limited in the afternoons. Your feeling will even become pleasant, with temperatures around normal. Nights and mornings will thus be cool and locally cold from Saturday, with values ​​of 4 to 7°C near the Massif Central, and 7 to 14°C from northeast to southwest. This drop will increase on Sunday morning, especially in the southwest, where you will lose 6°C in 24 hours. A risk of white frost will thus be possible near the Massif Central. This general pattern will then persist throughout the week.



Credit: The Weather Channel

The reliability of this weather pattern change is very high. It is less so in the detail of each day, because of doubts about the more or less significant presence of clouds in the north, and risks of mists and fogs in the southwest.

How to reduce consumption by heating less?

In the context of the energy crisis that we are experiencing, the hunt for expenses is open. And there are simple reflexes to adopt to maintain the temperature of your interior without turning on your heating, or by limiting it: close your windows, doors and shutters securely during the night. Conversely, as soon as the sun comes out, bring it in by opening shutters and curtains during the afternoons. If you heat, be sure to adapt the temperature according to your rooms: 19°C during the day for the living room and kitchen, and 17°C in the bedrooms. At night, or when you are away, you can lower the temperatures in the living room and kitchen by 3°C.

The thermal amplitudes will be strong between the cold of the morning and the very pleasant feeling with the sun of the afternoon. It will therefore be important to dress well to protect your health. It is therefore time to bring out the sweaters for the cooler hours, and to test the famous onion technique: for the most chilly and chilly among you, this technique consists of intelligently putting on several layers of clothing when it is cold, then to remove them gradually as soon as the temperatures rise, and all without making you cry!

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