Heat Exchanger

What Is a Heat Exchanger in a Furnace?

A heat exchanger is a critical component in your furnace that transfers heat to provide space heating. Not only does the heat exchanger help warm the home, it also keeps toxic combustion separate from the heated air.

How Heat Exchangers Work

In a gas furnace, the heat exchanger is a series of metal tubes located between the combustion chamber and the blower. If you have a non-condensing, or lower efficiency furnace (80% AFUE), there will  only be one heat exchanger, the 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 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 your furnace has a secondary heat exchanger, the combustion exhaust that leaves the primary heat exchanger will enter into the secondary heat exchanger.  In the secondary heat exchanger, additional heat is released from the flue gas and water vapor begins 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. 

Your furnace heat exchanger expands and contracts through thermal stress as it works to help heat your home. Keep reading to see how you can mitigate repeated wear and tear and prolong the life of this important furnace component.

Heat Exchanger Maintenance

Your heat exchanger can last for the life of your furnace with proper maintenance. For maximum efficiency and longevity, you should schedule a yearly furnace tune-up with a licensed HVAC technician. 

During furnace maintenance, 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.

As a homeowner, one of the simplest ways to  keep your furnace and all its components in top shape is by changing your filter regularly. This can be every 30-90 days based on the quality of your filters and whether you have an air purification system.

How to Know If There’s a Problem with Your Heat Exchanger

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

Watch, smell, and listen for these signs that you may have a problem.

1. Bad smell. A malfunctioning heat exchanger can give off a smell like formaldehyde, which some people describe as a pungent pickle-like smell.
2. Strange noises. The metal of the exchanger expands and contracts during the heating process. Cracks can lead to rattling and banging noises when your furnace kicks on.
3. Soot buildup. Soot buildup around your heat exchanger can mean it’s not fully burning the natural gas.
4. Visible cracks. If you or your HVAC technician sees visible cracks, this is a major problem.
5. A change in flame color. A healthy furnace has a blue flame. If the flame is yellow or orange, you may have a contaminated gas mixture.
6. Your carbon monoxide detector goes off. If your carbon monoxide detector in your furnace room goes off, it may be a sign you have a cracked heat exchanger. 

You should turn off the power to the furnace and call an HVAC technician. Open windows and doors to air out the home, and check on everyone in the home.

If you notice any of these signs of a cracked heat exchanger, or your HVAC technician does, you need to address the problem immediately, for the safety of you and your family.

Can You Replace a Cracked Heat Exchanger?

Theoretically, yes,  you can. This involves removing the damaged cell and replacing it. But other parts may need to be replaced at the same time. Because of this, dealing with a cracked heat exchanger is one of the most expensive furnace repair scenarios 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 further information.

If your HVAC system is aging out or needs more frequent repairs, check out our furnaces (both natural gas and oil) as well as our heat pumps. When paired with a furnace in a dual fuel system, a cold climate heat pump can effectively heat and cool your home in extreme temperatures.

Questions about heat exchangers and if there’s a problem with yours? Contact a Trane Comfort Specialist™ near you today.