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How Does Air Flow Through a Furnace

If you don’t stop to think about how your furnace works, it can sometimes
seem like warm air is magically coming out of your home’s vents.
But the truth is that by the time warm air is coming out of your vents,
it has gone through a series of stages and traveled quite a long ways
to get there. Knowing about the airflow process of your furnace can help
you understand how your heating system works and why it’s so important
to keep it well-maintained, so today we’re going to explain the
process by answering the question, “How does air flow through a


How does air flow through a furnace?


    • Air starts in your home’s rooms. Your furnace doesn’t “create”
      air, it simply cycles air from one place to another throughout your home.
      So the air that your furnace heats up actually originates in your home’s
      rooms. When your thermostat senses that the surrounding air has gotten
      too cool, it sends a signal to your furnace to turn on and begin pulling
      in that cool air to be heated up.


    • Air is sucked in through the return vents. When your furnace’s air
      handler is turned on, it creates a negative pressure in your return ducts
      that sucks in air from your home’s rooms. The access point to those
      ducts is the return vents. It’s important to make sure those return
      vents are completely open and clear of obstructions like furniture so
      that air can move easily into your ducts and toward your furnace.


    • Air is sent through the filtration system. Once air travels through your
      return ducts and reaches your furnace, it encounters your filtration system
      before it is heated. The air is sucked through the filter, and contaminants
      like dust and allergens get trapped by the filter so that only clean air
      is heated by your furnace. It’s at this point that your furnace
      can suffer from efficiency problems if your filter is dirty, because your
      air handler will have a hard time pulling air through a clogged filter.
      That’s why it’s so important to check and/or change your filter
      every month.


    • Air blows over the heat exchanger. After getting past your furnace’s
      filtration system, the air is ready to be heated. The air is blown over
      the hot outside walls of a heat exchanger, where it picks up heat and
      its temperature rises. This is the point where some furnaces encounter
      safety issues. If there are any cracks in the heat exchanger’s walls,
      carbon monoxide from inside the heat exchanger can leak out and get picked
      up by the air that’s blown over it and will be delivered to your
      home’s rooms. You can ensure this doesn’t happen to your home
      by scheduling a furnace tune-up before every heating season when your
      heat exchanger will be inspected for cracks.


    • Air is sent the supply vents. After passing over the heat exchanger and
      heating up, the newly warm and clean air is ready to be delivered back
      to your rooms. The air is blown into your home’s supply ducts, and
      it exits your ductwork via the various supply vents in your rooms. Just
      as with your return vents, it’s important that your supply vents
      are not blocked so that warm air can be properly delivered and distributed
      throughout your rooms. Once the warm air makes it to your rooms and the
      heating cycle finishes, it stays there until it cools back down, when
      the whole cycle begins again.


If you have any questions about how air flows through a furnace, or if
you’d like a heating system serviced or installed in your home,
contact Jerry Kelly, your
St. Louis furnace installation and repair contractor. We provide service all over the St. Louis area, including towns like
Ballwin, Chesterfield and Clarkson Valley, MO.