What must be true for an electric heating thermostat to function properly?

For an electric heating thermostat to function properly, it is essential that it opens on temperature drop. This ensures that when the room temperature falls below the set point, the thermostat will break the circuit, turning off the heating system to prevent overheating. Conversely, when the temperature rises to the set point, the thermostat re-establishes the circuit, allowing the heating system to operate when needed.

If the thermostat were to close on rise, it would mean that as the temperature increases, the device would open, which could lead to heating system operation when it is not required, risking overheating and discomfort. This characteristic of opening on drop is critical for maintaining a stable and comfortable environmental temperature.

An adjustable thermostat could improve user comfort by allowing for personalized settings, but it is not a fundamental requirement for proper operation of the heating system. The placement above the heat source or the ability to close on rise also do not directly contribute to the primary function of maintaining the desired temperature through opening on drop.