Which of the following is a component of a gravity hot-water heating system?

A gravity hot-water heating system relies on the natural principles of convection and gravity to circulate hot water throughout a building. The component that is central to this system is the boiler, which heats the water before it is distributed through the pipes. As the water heats up, it becomes less dense and rises, creating a natural flow throughout the system.

This system was commonly used in older constructions and works effectively without the need for pumps, relying solely on the physical properties of water and the design of the system. Boilers are specifically designed to generate hot water for heating systems, making them the essential component of a gravity hot-water heating system.

While fuel efficiency ratings, baffles, and condensing units may be relevant in the broader context of heating systems or specific modern heating technologies, they do not directly relate to the fundamental operation and components of a gravity hot-water heating system. Baffles are generally used in other types of heating systems to enhance efficiency or direct flow, and condensing units are typically associated with refrigeration and air conditioning systems rather than traditional gravity hot-water heating. Therefore, the boiler stands out as the key component necessary for the functioning of a gravity hot-water heating system.