What is the controlled variable in a heating system?

The controlled variable in a heating system is the temperature of the air. In this context, the primary objective of a heating system is to maintain a comfortable air temperature within a building or specific space.

When the temperature of the air is detected to be below a desired set point, the heating system activates to increase the temperature, ensuring the space remains within the desired thermal comfort range. This control loop typically uses a thermostat as the sensor to monitor the air temperature, and when it falls below the set point, the heating system makes adjustments to bring the temperature back up.

While airflow rate, hot water supply, and humidity levels can all influence the heating system's performance and comfort conditions, they are not the controlled variable, as the system specifically regulates to achieve and maintain the desired air temperature.