What element controls the heaters in the type H?

The correct choice identifies thermostats as the key element that regulates the heaters in the type H system. Thermostats are designed to monitor and control the temperature within a designated space. In the context of heating systems, they work by switching the heating element on or off based on the current temperature relative to a predefined set point.

When the temperature drops below the set point, the thermostat activates the heater to raise the temperature to the desired level. Likewise, once the temperature reaches the set point, the heater is turned off. This process ensures that the environment remains at a comfortable and efficient temperature, preventing overheating or excessive energy consumption.

In this case, while timers could offer scheduling capabilities, and pressure regulators might control pressure in some systems, they do not play a role in the direct management of heating based on temperature. Thermometers simply provide temperature reading without the ability to control the heaters, making them unsuitable for the purpose of controlling heater operation within type H systems.