How Do I Know If My Furnace Heat Exchanger Is Bad?

How Do I Know If My Heat Exchanger Is Bad? 

What Is A Heat Exchanger In A Furnace?

The furnace heat exchanger is a thin metal piece between the combustion chamber and the blower. As the combustion chamber heats the exchanger, heat is transferred to the air being blown across the surface. This air is free of the flue gases and sent on through ducts to provide heat inside your home.

In short, it takes the heat energy from the combustion and transfers it into air that’s safe to breathe.

Your heat exchanger must have an air-tight seal to keep the flue gases out of your home because the gases produced in the combustion can be hazardous to your health, including carbon monoxide which can be deadly.

Do Electric Furnaces Have Heat Exchangers?

Electric furnaces don’t use heat exchangers because it doesn’t burn fuel. It heats the air directly as it passes over hot coils that are heated by electricity.

Heat Exchanger Furnace: How Do I Know If It’s Failed?

A gas furnace heat exchanger should last a good 10-20 years, but it will eventually fail. That’s because of the way your furnace works.



Metal expands when it’s heated and contracts when it cools. Over time, the cycle of expansion and contraction can cause metal fatigue. This can bend the metal in the heat exchanger and cause it to crack or break. When this happens, it can break the seal that separates the flue gases from your airflow and create a dangerous situation that needs service from a qualified professional.

Bad Heat Exchanger Symptoms

To determine whether your heat exchanger needs to be replaced, it takes a visual inspection. Technicians can use an infrared video inspection to diagnose the health of the heat exchanger and determine whether it needs replacement.



Here are some of the warning signs that might mean the ereheat exchanger in your furnace is going bad.

Changes In Flame Color

When your gas furnace is working properly, it produces a blue flame. Within the sealed chamber, it should also burn steadily without flickering. When it burning erratically, or the color has changed to yellow, it can be a signal that oxygen is getting into the chamber through a damaged heat exchanger.

Discolored Metal Or Soot Buildup

When a heat exchanger cracks, it can get discolored from soot build-up. The cracks break the seal from the combustion chamber and let soot come through to the other side. You may notice dark spots where the crack occurs.



You may also notice soot building up within the furnace, which indicates the burner is not functioning properly. The soot comes from carbon buildup when the furnace doesn’t burn the gas completely. It may be from faulty burners or a cracked heat exchanger.

Carbon Monoxide Detected

Carbon monoxide can be a by-product of the combustion process. It’s an invisible gas that doesn’t have an odor. If it builds up inside your home, it can be deadly. That’s why the Center for Disease Control recommends every home has a CO detector in place and gets annual checkups for your furnace.



Carbon monoxide can be a symptom of a cracked heat exchanger that allows the gas to get into your air supply. If you have CO detectors and they go off, it’s serious. Immediately open windows to let in fresh air, turn off your furnace, and leave your home. Once you’re safely outside, call for help. If you need medical attention, call 911.

Strong Odors

While carbon monoxide is odorless, other gases can be smelled. If your heating system emits a strong unpleasant smell, it could be a sign your heat exchanger is bad. Some liken the smell to formaldehyde. It can also be toxic. If you smell it, call a qualified technician.

Excess Condensation Or Water On The Floor

If you notice an excess of condensation on your heating system or water on the floor at the bottom of your gas furnace, you might have a clogged internal drain or a leak in your humidifier system connected to your furnace. A cracked heat exchanger might also be the culprit.

Clogged Heat Exchanger

Dirt and dust can accumulate in your furnace and block filters, blowers, and coils. This buildup can lead to a clogged heat exchanger and prevent air from flowing efficiently through the system.

Poor Heating

When there’s a damaged heat exchanger, the efficiency of your furnace is compromised. The furnace will have to work harder to produce warm air to heat your home. You may notice poor performance and a significant increase in your utility bill.

What Should I Do If I Think My Heat Exchanger Has Failed?

If you experience any of these warning signs or suspect your furnace has a cracked heat exchanger, you’ll want to contact a professional HVAC contractor to inspect the furnace. It’s not something you should tackle yourself and it’s not something you should put off. Continuing to operate the furnace with a cracked heat exchanger can put your health at risk. The best advice is to shut down the system and get a qualified technician to take a look.

If an inspection has determined that metal fatigue has occurred and led to cracks – even tiny ones that are difficult to see – it’s time for a replacement.

A cracked heat exchanger is not repairable. It will need to be replaced. If your heat exchanger isn’t covered by a manufacturer warranty, it can cost between $1,500 and $2,000 to replace it. Warranties typically only cover the cost of the heat exchanger, so even if it’s covered, you will likely have to pay for the labor which can cost an average of $500.



You’ll also want to consider the age of your furnace. Replacing your heat exchanger may not be worth it if your furnace is older. Also, a cracked heat exchanger may itself be a symptom of another problem in your furnace, such as overheating. You might spend the money to replace the heat exchanger only to find out there’s a bigger problem that will also need to be repaired.

How Do I Prevent My Heat Exchanger from Failing?

To keep your furnace running properly, it’s advised that you have regular checkups at least once a year. While you can’t prevent your heat exchanger from cracking due to the heating-cooling cycles that occur as part of the heating process, a checkup can detect the warning signs and take action before you have a problem.



One simple way you extend the life of your heat exchanger and furnace is to make sure you replace air filters before they get dirty. A clogged air filter can limit the airflow through the furnace. This can cause overheating of elements and lead to additional stress from expansion and contraction.