What type of heating system uses a circulating pump?

The correct choice is the hot water heating system, commonly known as a hydronic system. This type of heating system utilizes a circulating pump to move warm water through pipes that connect to radiators or heated flooring. The circulating pump ensures that hot water flows efficiently from the boiler, where it is heated, to the areas requiring heat, facilitating consistent and effective heating throughout the space.

In contrast, forced air furnaces distribute heated air through ductwork using a blower fan rather than water, making them reliant on air movement instead of a circulating pump. Similarly, a forced air burner is more about the combustion process used to generate heat and also does not utilize circulating water. A gravity coal furnace relies on the principle of gravity for heat distribution and natural air movement rather than a mechanical pump, which limits its efficiency compared to hydronic systems. Thus, the hydronic system's use of a circulating pump is crucial for its operation and is what distinguishes it from the other heating types listed.