What is a Furnace Heat Exchanger? | What are the signs of a cracked heat exchanger?

What is a Furnace Heat Exchanger?

A furnace heat exchanger is a thin sheet between the blower and the combustion chamber. When a combustion chamber adds heat to the heat exchanger, the heat or thermal energy transfers to the air that blows over the surface. This air does not contain exhaust gases and is delivered to the ducts to supply heat to the house.

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In other words, a furnace heat exchanger draws thermal energy from the burning process and releases it into the air to ensure a safe breathing environment.

furnace heat exchanger
Furnace Heat Exchanger

In short, the furnace heat exchanger is a component of your furnace which has the responsibility to maintain separation of the combustion process and air (oxygen) for your proper breathing.  It is very important to stop the intoxication of carbon monoxide.

Since the gases formed during combustion (such as carbon monoxide) are harmful to health. Therefore, heat exchangers should contain an air-tight seal to prevent combustion gases from entering the house.

What is a Cracked Heat Exchanger?

A cracked heat exchanger is a most hazardous thing that may cause furnace problems. As the heat exchanger cracks, the unburned gases like nitrous oxide, sulfur dioxide, and carbon monoxide may leak and enter your house.

An excessive quantity of carbon monoxide in a house can produce severe health issues like sick or may also cause death.

Cracked Heat Exchanger
Cracked Heat Exchanger

As the homeowners learn about the hazards of a cracked heat exchanger, they want to know what they should do to stop problems in the first place. Today in this article, I am going to tell you how to prevent the cracked heat exchanger in the furnace!

How does a Furnace Heat Exchanger Work?

The principle of operation of the furnace heat exchanger is to exchange (or transfer) the thermal energy generated in the combustion chamber to the outside of the device and blow it into the entire house installation system via a blower. Basically, this process completes in the following three steps.

For example, consider a gas-powered HVAC system that is one of the most famous residential used systems.

Furnace Heat Exchanger working
  1. First of all, the furnace needs heat to start the burning process. The hot flue gases produced due to the burning process goes into the heat exchanger chamber and heat the metal wall there.
  2. After this process, the return air duct draws cool air out of the house and blows it out of the exchanger. As the cold air passes through the exchanger, heating walls, and different rooms of the house, it converts into hot air. This process maintains a separation between the breathing air and the combustion gas.
  3. The gas produced during the burning process leaves the exchanger and leaves the vents outside the house. The operating modes of the high-efficiency condensing furnaces differ slightly. In such types of furnaces, the gas passes by a second heat exchanger and absorbs additional heat for domestic use.

How does a heat exchanger develop cracks?

  1. Normal wear and tear: A heat exchanger heats and cools with each heating cycle and your building experiences many heating cycles all over the day. During each cycle, the walls of the heat exchanger heat up and cool down; due to that, they contract and expand. With the passage of time, this repeated expansion and contraction can cause cracks in the exchanger wall.
  2. Low-quality repair and installation: If you install or repair your furnace by an inferior contractor, the chance of damage to the heat exchanger will be very high. The low-quality contractors don’t properly install or repair your furnace, which generates different issues.
  3. Dirty air filter: Dirty air filters are another common reason for the cracked heat exchanger. These dirty filters block airflow into the furnace. This blockage restricts and overheats the amount of air that flows through the exchanger. If this issue occurs frequently, the heat exchanger can crack.
  4. Closed or blocked vents: When the house’s return vents and air supply is blocked, airflow issues arise in the furnace for the same reason that the air filter becomes dirty and the heat exchanger cracks.

Symptoms of a Cracked Furnace Heat Exchanger

The most common signs of a cracked heat exchanger are given below:

  1. Poor Heating
  2. Presence of CO
  3. Strange or Unpleasant Smell
  4. Audible Sounds
  5. Soot Build-up or Discolored Metal
  6. Change in the flame appearance
  7. Corrosion & Cracks

1) Strange or Unpleasant Smell

When a heat exchanger cracks, it generally produces an unpleasant or strange smell similar to that of formaldehyde.

2) Soot Build-up or Discolored Metal

A cracked or blown heat exchanger starts building white soot in or around the furnace burner.

3) Corrosion & Cracks

You must immediately contact to a specialist technician when you observe cracks or corrosion on furnace parts (e.g., induction motors or draft diverter box).

4) Change in the flame appearance

In the case of some ovens, you can see the flames that heat your room air. If you observe yellow or orange, it means your furnace has problems, and you must contact a specialist.

5) Audible Sounds

If your heat exchanger has been cracked, you may hear some rattling noises when switched on the thermostat. As we know that metal is used for the construction of the heat exchanger. Therefore, when it heats up, cracks expand or contract and produce banging, popping, or rattling noises.

6) Presence of CO (Carbon Monoxide)

CO is a flammable, tasteless, colorless, and odorless, poisonous gas. If the heat exchanger fails, carbon monoxide can get into the house. Therefore, you must use a CO alarm or detector which will warn you of the presence of carbon monoxide but don’t only trust on CO alarms to detect a cracked heat exchanger.

Because sometimes, failed or damaged CO alarms can’t detect the presence of CO, and an extensive quantity of CO can lead your death. Therefore, it is advisable to check the heating system and the furnace at least once a year.

CO leakage from the cracked heat exchanger

7) Poor Heating

A cracked heat exchanger reduces the furnace efficiency. In such conditions, the furnace starts consuming more fuel to work harder to generate hot air to heat your rooms or building. You can easily observe it by the poor heating of your furnace and an increase in your utility bills.

How can you prevent a cracked heat exchanger?

  1. Schedule annual furnace tune-ups: Cracks in the heat exchanger may also develop with time, even if you properly take care of your furnace. Therefore, the annual maintenance of the whole system is very important. In annual maintenance, the maintenance person checks the cracks of the exchanger and fixes small cracks before they convert into major problems.
  2. Keep vents clear and open: You always need to be ensured that all vents and air inlets in the house are fully open and clear of blocks like furniture and other items. This is one of the easy methods to stop airflow problems that can cause the heat exchanger to explode.
  3. Change your air filter on time: By constantly adding new filters to the furnace, you can stop main airflow problems that can cause the exchanger to crack or overheat.

Read Also: Working of HVAC system

Advantages of a Furnace Heat Exchanger

FAQ Section

What tools are needed to determine if a Heat Exchanger is bad?

One of the best methods to tell whether a heat exchanger is defective or not is to check it deeply or just inspect it visually.

Nowadays, the old flash and mirror backup method has been exchanged with the latest tech infrared video inspection system. This latest technology has improved the development of the heating industry, just as arthroscopy has improved medical surgery. With this new technology, the technicians can see cracks that cannot be seen with just a mirror.

Is a Heat Exchanger inspection foolproof?

You can use mirrors and flashlights to get access to a furnace heat exchanger for some places, but most heat exchangers are invisible.

When a technician uses an infrared video inspection system, there is no need to completely disassemble the furnace and remove the heat exchanger, which can be done as reliably as possible.

What are the options if a Heat Exchanger is bad?

If your heat exchanger has been cracked or damaged, you have the following two options: 

  1. Firstly, you need to replace your furnace or heat exchanger. If you have a warranty on your system, you must immediately claim for exchange. This option will also save your money.
  2. If your system has minor or controllable damage or crack, you must immediately contact the best technician to fix it.

What are the signs of Cracked Furnace Heat Exchanger?

  1. Corrosion & Cracks
  2. Presence of CO
  3. Change in the flame appearance
  4. Poor Heating
  5. Audible Sounds
  6. Wear & Tear
Read Also
  1. Different types of HVAC systems
  2. Types of Heat Exchangers
  3. Types of Plate Heat Exchangers

3 thoughts on “What is a Furnace Heat Exchanger? | What are the signs of a cracked heat exchanger?”

  1. I have heard about the furnace releasing hazardous gases like carbon
    monoxide if the heat exchanger is not changed, but I always thought it was just a myth, so I wasn’t bothered to change it. A few weeks back, my kids started to complain about a foul smell coming from the furnace, and that’s when I knew that my heat exchanger had been cracked. Thank you for sharing this article. It will help a lot of people who aren’t aware of the importance of changing a heat exchanger.

    Reply
  2. The average costs for replacing your exchanger is about $1,500. However, it can cost as little as $500 or as much as $3,500. If the heat exchanger is cracked or malfunctioning before you would typically expect it, there may be another issue with your HVAC system. If your Heat Exchanger has been deemed cracked by a HVAC professional you should NOT be running it. Unfortunately, some owners will attempt to run their furnace even when a cracked heat exchanger has been detected.

    Reply

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