Final answer:
The thermostat controls the 1st stage of secondary heat in a heating system, activating supplemental heat when needed to achieve desired temperature levels.
Step-by-step explanation:
What control operates the 1st stage of secondary heat? The correct answer is c) Thermostat. In a heating system, the first stage of secondary heat typically refers to the initial phase of providing supplemental or additional heat. This heat is necessary when the primary heating stage cannot maintain the desired temperature setpoint alone.
The thermostat is responsible for detecting the temperature within a space and activating the heating system to bring the temperature up to the desired level. If the thermostat determines that the primary heat source is insufficient to achieve the set temperature, it will activate the secondary stage of heating.
The other options, such as pressure switch, temperature controller, and flow meter, play different roles in heating systems.
A pressure switch is commonly used to detect pressure changes and ensure safety, a temperature controller manages the temperature of a specific process or area, and a flow meter measures the flow rate of a liquid or gas within the system. These components are not typically directly responsible for activating the secondary heat stage.