Furnace Heat Exchangers - What is a Heat Exchanger in a Furnace?

Furnace Heat Exchangers - What is a Heat Exchanger in a Furnace?

Modern air conditioners and furnaces can be complex pieces of machinery.  It is not uncommon for HVAC contractors (what does HVAC stand for?) to throw around technical terms and parts, either because they are just too used to doing it at work or, in unfortunate circumstances, because they are trying to take advantage of a customer.  As your educator, All Systems Mechanical will spend today’s post answering the question, ‘what is a heat exchanger in a furnace?‘  There are many parts to a modern furnace, but the furnace’s heat exchanger is one of the most important.  Simply put, the furnace heat exchanger is the part that heats your air, but in this post we will dig a little deeper and help ensure that you are ready to talk to your furnace repairman using the same technical terms and understanding that he does.  We will do this by first explaining what a furnace heat exchanger is, how it works, what type of fuels can be used and finally how a damaged heat exchanger can be dangerous.

furnace heat exchangerWhat is a Furnace Heat Exchanger?

A furnace’s heat exchanger is a set of tubes or coils that are looped repeatedly through the air flow inside your furnace for the purpose of heating air.  Simply put, the furnace heat exchanger is the part of your furnace that actually heats the air.  What shape these coils take is dependent on what model of furnace you have, as well as what type of fuel that your furnace uses for combustion.  For information on different furnace brands, try: Lennox vs Carrier Furnace Review.

How does a Furnace’s Heat Exchanger Work?how furnace heat exchanger works

Your furnace’s heat exchanger works using a very simple principle that, believe it or not, you are already familiar with.  Imagine that it’s cold outside, and you just ordered a hot cup of soup at your favorite restaurant.  Ouch!  It’s a bit too hot, so what do you do?  You blow on the soup, right?  This is exactly how your furnace heat exchanger works.  In this example, the heat exchanger is your soup, and the hot air that you are blowing off of the soup is the hot air that circulates through your house.  A furnace’s heat exchanger uses some type of fuel to combust inside of it, creating heat and getting very hot.  Your blower motor (aka your ‘fan’) then blows air over this heat exchanger (like blowing over hot soup) and into your ductwork, where it is distributed throughout your house.  That’s it – it really is that simple.

What Types of Fuel Can Be Used By A Furnace’s Heat Exchanger?

A furnace’s heat exchanger can use all sorts of fuel, and the type of fuel your furnace uses depends on preference, local climate and what type of fuel is readily available in your area.  For instance, propane might be readily available in Bozeman, Montana but it is unlikely that you’d find propane as a means of furnace fuel in an off-gridder’s house in Alaska.  This is because they don’t have roads to their house and can’t have it delivered!  Your furnace heat exchanger can use many types of fuel, including: Propane (LP) Gas, Fuel Oil, Natural Gas and Electric.  Some fuels are more efficient than others:

furnace heat exchanger fuel comparison chart

Which one you choose depends on some of the above factors.  As you can see, an electric furnace is the most expensive means of heating your house, but electricity is also 100% efficient, meaning that all of it is translated into usable heat by your house.  Make the decision by first examining what type of fuels are available in your area!  Prices can vary depending on supply and availability:annual fuel cost graph furnace heat exchanger

Is a Cracked Heat Exchanger Dangerous?

cracked furnace heat exchangerYes, a cracked or damaged furnace heat exchanger is a major danger to you and your family.  Remember that your furnace is burning some type of material in order to generate heat, but this process should be taking place inside your furnace’s heat exchanger itself.  If your heat exchanger is cracked or damaged, all sorts of dangerous gasses can be leaked into your home, including carbon monoxide – aka “the silent killer.”  For more information on carbon monoxide and how it can be dangerous, take a look at the Wiki page: Carbon Monoxide.

How Can I Keep My Family Safe from Carbon Monoxide?

There are a couple of ways to keep your family safe from a cracked furnace heat exchanger:

  1. Make sure your house or business is filled with the proper amount of carbon monoxide detectors.  Fire detectors aren’t enough, these detectors will detect carbon monoxide in the air before it can incapacitate you.
  2. If you have a furnace, make sure that you have it inspected annually, or every other year at a minimum.  If you don’t want to spend the money for your local HVAC contractor to come out, this inspection is something easy that you can do yourself.

No one can inspect your furnace as good as a contractor can, who has endoscopic cameras and other tools, but in order to learn how to inspect your own heat exchanger, take a look at the following do-it-yourself video; it is short and informative: Furnace Heat Exchanger Inspection.

Save Money on Your New Furnace by Watching This Short Video

For those who are in, or are soon to be in the market for a new furnace or air conditioner, make sure that you don’t get ripped off!  See what a fair price should look like.  Here’s a short video on how we can help:



Final Thoughts on a Furnace’s Heat Exchanger

Your furnace’s heat exchanger is one of the most critical parts of your furnace.  It is not only responsible for heating the air inside of your home, but it can be dangerous if not cared for properly.  Don’t get worried, modern heat exchangers have an abundance of safety features, so if you make sure that you do your part by having your furnace’s heat exchanger inspected regularly and ensuring that you have carbon monoxide detectors in your home, you’ll be safe and sound.  For more information troubleshooting problems with your furnace, take a look at: Furnace Not Blowing Air? and Why is my Heater Blowing Cold Air?, or just visit the ASM Air Conditioning Blog.  If you have more questions or if you live in the Santa Clarita or Los Angeles area, please feel free to give us a call.  We’d be happy to help you:


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Timothy Kautz
About the author
Tim K.

The University of Virginia - 2005 / The Wharton School of Finance - 2016 / U.S. Naval Aviator 2005-2015. At All Systems Mechanical air conditioning and heating, we believe that the experience our clients have is every bit as important as the products they receive. Simply put, our results speak for themselves, and we'd be happy to help. If you're in the market for a new AC or furnace, make sure that you get a fair price! Try our online calculator; click the tab on the top of this page for more information.

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