Final answer:
The main type of heat transfer that occurs when a furnace heats an entire room is convection, which circulates warm air throughout the space.
Step-by-step explanation:
The type of heat transfer that takes place when a furnace heats up an entire room is primarily convection. Convection is the heat transfer by the macroscopic movement of a fluid, which in the case of a room, is the air. When the furnace heats the air, it becomes less dense and rises, and the cooler, denser air sinks, creating a convective current that evenly distributes the heat throughout the room. While radiation and conduction also play a role in heating the room, convection is the dominant mode in this scenario due to the circulation of air.