A steam heating system is a type of:

The correct answer is that a steam heating system is classified as a hydraulic system. This classification is based on how steam heating systems operate—using water as the heat transfer medium. In steam heating, water is heated to create steam, which then travels through pipes to radiators or other heat emitters, transferring heat to the surrounding air. The use of water and steam under pressure is a defining characteristic of hydraulic systems.

The other options do not accurately describe steam heating systems. For instance, forced warm air systems use air as the heat transfer medium, relying on a blower to distribute heated air throughout a space. Resistance heating systems generate heat directly through electrical elements, while radiant heating systems primarily involve heating surfaces that then radiate heat into a room, using techniques such as electric cables or heated water in floors. Therefore, these definitions clarify why steam heating systems are best categorized as hydraulic systems.