The doubt appears with the first cold nights: does it use less to turn off the heating or to leave it running at minimum to prevent the house from cooling down? The general recommendation of the Institute for the Diversification and Saving of Energy, IDAE, is to turn it off during the night and adjust its operation to the hours in which the dwelling is used.
The agency explains that, when sleeping under covers, a temperature between 15 and 17 degrees may be sufficient. It also considers more efficient, as a general rule, to turn it off during the night than to keep the system continuously on.
When it may make sense to leave it at 15 or 17 degrees
IDAE itself contemplates an exception: very poorly insulated homes that lose a lot of heat during the night. In those cases, it proposes keeping the heating on with the thermostat between 15 and 17 degrees.
Therefore, the recommendation does not consist of letting any home cool down without limit. The decision depends on how much the indoor temperature really drops and on the characteristics of the house.
A thermometer helps to check it. The outdoor temperature alone does not indicate how an intermediate floor, a top floor, or a detached house behaves.
Ventilate before turning it back on
For the morning, IDAE recommends ventilating, closing the windows, and then turning on the heating. Opening for a few minutes makes it possible to renew the air while avoiding an unnecessary loss of heat.
The agency places around 21 degrees as a sufficient temperature to maintain comfort during the day with appropriate clothing. It also advises taking advantage of natural light and adapting the use of the heating to the occupancy of the home.
The savings are not the same in all houses
This advice cannot be turned into a fixed euro amount. The result depends on the insulation, the climate, the equipment used, its regulation, and the price of energy.
The useful check consists of observing the indoor temperature and consumption over comparable days. Keeping a house warmer than necessary for hours when no one takes advantage of that heat can increase spending without improving comfort.