What is an HVAC Heat Exchanger?

By Anne Fonda

In your HVAC system, a heat exchanger transfers heat from one area to another. In an air conditioning or heat pump system, we call the heat exchanger the condenser coil. For this article, we will focus on the furnace heat exchanger.

The heat exchanger is a critical furnace component that transfers heat to provide warm air throughout your home. Not only does the exchanger help warm the indoor air, but it also keeps toxic combustion gases separate from the heated air.

The heat exchanger is a series of metal tubes located between the combustion chamber and the blower in your furnace. If you have a non-condensing, or lower efficiency furnace (80% AFUE), there will only be one, or primary, heat exchanger. If you have a condensing, or higher efficiency furnace (90%+ AFUE), you will have both a primary and a secondary heat exchanger. 

When a furnace burns natural gas, fuel oil, or propane fuel, its exhaust/combustion by-products enter and travel through the primary heat exchanger. The hot flue gas heats the metal as the gas makes its way to the exhaust outlet of the furnace. As this occurs, the hot metal heats the air circulating over the exterior of the heat exchanger.

If you have a secondary heat exchanger, the combustion exhaust that leaves the primary heat exchanger will enter into the secondary unit.  The secondary heat exchanger releases additional heat from the flue gas, causing water vapor to form. This change of state from water as a vapor to a liquid releases latent heat in the secondary heat exchanger, bringing the furnace to an even higher level of efficiency. 

The metal tubes expand and contract through thermal stress during this process.

A heat exchanger can last 20 years or more. The American Standard warranty covers our furnace heat exchangers for 20 years or the life of the furnace, depending on the unit and your warranty.

Increased wear and tear, dirty filters, clogged air ducts, and improperly sized equipment can lead to problems.

To get the most out of your heat exchanger and your furnace as a whole, schedule yearly furnace maintenance with a licensed HVAC technician. During a furnace tune-up, the technician will give an overall health check of your furnace. This includes checking your exchanger for cracks. A cracked heat exchanger can result in gas leakage.

You can help maintain your furnace and all its components by changing your filter every 30-90 days based on the quality of your HVAC air filters and whether you have an air purification system.

The most common problem with your exchanger will be cracking due to repeated expansion and contraction. A cracked heat exchanger can lead to the leakage of gases, which can be dangerous and even deadly.

Smell, look, and listen for these signs that you may have a problem.

If you notice any of these signs of a damaged heat exchanger, or your HVAC technician does, you need to address the problem immediately, for the safety of you and your family. You should turn off the power to the furnace. Open windows and doors to air out the home, and check on everyone in the house.

Yes, but it might not be cost-effective. Replacing the heat exchanger involves removing the damaged cell and replacing it. But you may need to replace other furnace parts at the same time. Because of this, dealing with a cracked heat exchanger is one of the most expensive furnace repairs there is. 

If your furnace is more than 10-15 years old, a more cost-effective solution might be to get a new furnace. Read through our Repair or Replace Guide for more information.

Do you have questions about your furnace? Contact your local American Standard dealer for help.

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need. 

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by John Kim, Senior Product Manager, Furnaces