Which of the following must be true about the heating system in facilities?

The statement that central heating must be maintained at 75 degrees reflects important regulations related to the comfort and safety of building occupants. Maintaining a specific temperature ensures that spaces are adequately heated during colder months to protect against health risks such as hypothermia and to create a conducive environment for the work or living conditions of the facility's inhabitants.

This regulation helps to ensure that heating systems are not only functional but also operate within a set standard that promotes the well-being of individuals inside the facility. A consistent temperature also contributes to the overall efficiency of the heating system and reduces fluctuations that might lead to discomfort or increased energy costs.

In contrast, other options may not align with best practices or regulatory standards regarding heating systems. For instance, while space heaters might provide additional heat, they can also pose safety risks if not monitored properly. Coil heating systems may not meet all required safety and efficiency criteria in some facilities, and the use of portable fans could be inappropriate in a heating context, especially during cold weather.