It is the rare homeowner who thinks very much about his home heating furnace except if it has a problem. Furnaces can last quite a few years, and people generally just expect the furnace to work. Your furnace, however, needs to be tuned up each year in order to get the maintenance it needs to keep running without problems for all those years. You might even want to learn more about how it works, and thus the question: how do forced air heating systems function? might be a relevant question to...