The furnace is the heart of any heating system, whether forced-air, circulating hot water, or steam. Most household furnaces today are heated by gas or oil. To operate properly and efficiently, these furnaces require regular adjustment and periodic care. If carefully maintained, however, modern furnaces are economical heat producers and will provide years of dependable service, often equal to the life of the house. Here are the basics for understanding how typical systems work.
You can feel radiant heat being emitted directly from the hot surface of an appliance, but convected heat warms the air that comes into contact with the hot surface, As the warmed air rises toward the ceiling, it allows cooler air to flow in around the appliance, and this air in turn is warmed and moves upward, Eventually, a steady but very gentle circulation or air takes place in the room, and the temperature gradually rises until it reaches the setting on the room.