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 ask. A heating cycle is initiated when the thermostat detects the room temperature has dropped below the level set. This turns on the blower which sucks room temperature air through the return ducts into the heat exchanger where it is heated by gas jets, usually fueled by natural gas, but other fuels like propane are also used. The warm air is then circulated through the house via the air ducts, and the cycle ends when the thermostat reads a higher temperature and turns the system off. Furnace repair Thornton, Colorado, has more information about forced air furnaces and can also give you tips about using less energy and saving money on heating bills.