A programmable thermostat or programming thermostat is a device that is used to maintain the temperature of a room (or another place) at different levels depending on the time or day of the week. It consists of a thermostat and an electronic device (currently, formerly clockwork mechanisms) that varies the set point of the room temperature, automatically and at certain times, according to the user's wishes.

The use of this device can lead to significant energy savings. The heat losses of a home, whether isolated or an apartment in a neighboring building, or any other inhabited building, depend on the temperature difference between the outside and the inside. The amount of savings depends on the outside climate, generally defined by a calculated outside temperature for heating; This temperature is reached only on a few days during the heating season, with the other days having a higher outside temperature. It can be said, with sufficient approximation, that the average outdoor temperature throughout the heating season is the arithmetic mean between the calculated outdoor temperature and the outdoor temperature at which heating is no longer needed (between 18 and 20 °C).

To give an example and simplify, if the calculated outdoor temperature is 0 °C, and 20 °C is the temperature at which heating is no longer needed, the average outdoor temperature will be 10 °C. Normally, for each degree that the set temperature is increased, consumption will increase by 10% and, correspondingly, for each degree that it is lowered, it will decrease by the same amount. If the calculated outdoor temperature is lower, the decrease in consumption will also be smaller.

The programmable thermostat allows you to lower, at certain times, the temperature of the indoor environment by a few degrees automatically, achieving energy savings during that time. These hours are those when the house is empty (children at school and parents working) or at night, when being in bed, under a good blanket, the temperature can be lower in the rooms.

The thermostat is set with two set temperatures: one, the one for the hours of inhabited house, at about 20 °C and another reduced one, between 4 and 6 °C less, for the hours of sleep or empty house. In the example cited above, the savings would be 50% at those times, and even greater, because precisely the minimum daily temperatures occur during the night. With this programmable thermostat, if the normal operating temperature is set at 20 °C and the reduced temperature at 15 °C, on average at these times you will be saving 50% of consumption.