What Is A Furnace Heat Exchanger? The Beginner’s Guide


Rima Chatterjee

Furnace Heat Exchanger


Did you know there are two types of furnace heat exchangers? Primary and secondary. It helps keep toxic gases like carbon monoxide out of your home by venting them out through an exhaust pipe. But, over time, soot can build up, causing cracks and overheating. This can also let out dangerous gases, so regular maintenance is a must.

Moisture and corrosion can cause metal fatigue, so plates or coils may need repair or welding. Even with proper maintenance, excessive use or exposure to highly corrosive vapors can cause damage too extensive to repair.

If your heating system is making strange noises, or not warming or cooling properly, it could be a sign of a failing heat exchanger. Or, even worse, a crack in the device. Contact an HVAC technician ASAP to keep your family safe.

what is a furnace heat exchanger

Types of Furnace Heat Exchangers


To learn about the different types of furnace heat exchangers, you need to know about the primary heat exchanger and secondary heat exchanger. 

The primary exchanger is the first point of heat exchange from the combustion process. On the other hand, the secondary exchanger exchanges heat from the remaining flue gases before they are exhausted out of the system. Understanding how each of these two types works is crucial for homeowners to maintain their heating systems efficiently.

Primary Heat Exchanger

The furnace’s “heart” is the key component for heat exchange. It transfers heat from combustion gases to warm air or water, based on the furnace’s setup.

It’s vital for efficient heating and cooling, and it’s made of steel, stainless steel, or cast iron. It can be tubular or plate type, and used for forced air systems or hydronic systems.

It’s built tough to last, but you should clean and service it regularly for optimum performance and extended lifespan. Who needs a second heat exchanger when you can just snuggle up to your furnace?

Secondary Heat Exchanger

A Secondary Heat Exchanger is a device situated downstream of the primary heat exchanger. It captures any residual heat and transfers it to the air stream, increasing the furnace’s overall energy efficiency.

Attributes of a Secondary Heat Exchanger include type (plate or tubular), material (aluminized steel, stainless steel, or titanium), location (downstream of primary heat exchanger), and efficiency range (90-98%).

Not all furnaces have a secondary heat exchanger, however high-efficiency furnaces benefit from their presence, by raising their AFUE rating & saving energy costs in the long run.

For optimal efficiency & longevity of your furnace’s secondary heat exchanger, make sure to follow the manufacturer’s recommended maintenance schedules. Unsung heroes like these metal tubes help keep us warm, so let’s take care of them.

How Furnace Heat Exchanger Works


To understand how your furnace heat exchanger works and solve any related issues, I highly recommend learning about the combustion process and heat transfer in this section. 

Combustion Process

Heat transfer in a furnace is complex. Fuel and air mix, and then ignite. Flames heat the walls of the exchanger. This transfers heat into the home’s ducts for warmth.

For optimal performance, burner efficiency and airflow must be considered during installation. Maintenance is required to keep the furnace functioning. Different types of furnaces may have different combustion processes. For example, natural gas has pilot lights, and electric has heated coils.

One homeowner shared how their faulty furnace led to carbon monoxide poisoning due to incomplete combustion. This shows the importance of routine inspections by professionals to detect potential hazards and avoid tragedy.

Heat Transfer

Thermal energy transfer involves the movement of heat between objects. It is done through conduction, convection, and radiation. 

This heat exchange is important in various heating systems, such as furnaces.

The methods and examples of different types of Heat Transfer:

MethodExample
Conduction: Direct heat exchange through solid objects or materials.Touching a hot stove or spoon.
Convection: Heat transferred via fluid movement, like water or air currents.Boiling water or using fans to spread heated air.
Radiation: Heat sent out by an object in the form of infrared radiation. It travels until it reaches another object.The sun’s warmth on the earth or standing near a fireplace.

In a furnace’s heat exchanger system, combustion gases move in a closed chamber and pass their thermal energy to the metal walls around them. Once these walls are hot, air is pushed over them with force using fans. The warmed air is then spread throughout the building through ducts.

To avoid problems with the furnace’s heat exchanger, it is best to have regular maintenance checks done by professionals. Clean filters often and keep flammable objects away from your appliances. This will help you to enjoy warm comfort in your home throughout the winter without any difficulty.

Common Problems with Furnace Heat Exchanger


To address common problems with furnace heat exchanger, such as soot buildup and corrosion, cracks and metal fatigue, overheating and damage, you need to undertake routine maintenance on your heating system. 

Neglecting it may result in toxic gas exposure, health hazards and system breakdowns. In this section, we’ll cover the above-mentioned sub-sections in depth.

Soot Buildup and Corrosion

Sediment and rust can accumulate in heating systems, worsening over time. This can cause a decrease in efficiency and damage components. Rust can also form on pipes due to moisture or humidity, weakening them and shortening their lifespan.

To avoid these issues, inspect your unit for corrosion or sediment, replace filters, make sure there’s good ventilation, and install CO detectors

Cracks and Metal Fatigue

The furnace’s heat exchanger may suffer from fractures and metal fatigue. This can be due to fluctuating temperatures, bad upkeep, or low-grade materials. Corrosion and oxidation can cause cracks and weaken the metal. Moreover, regular use can also cause fatigue.

These issues let air into a heating cycle through cracks. This is dangerous, as it releases hazardous carbon monoxide. To prevent this, have a certified technician do routine maintenance every year. And, always have working carbon monoxide detectors in your home.

One homeowner noticed her furnace wasn’t running right and smelled something off. An expert technician found the heat exchanger had cracks that were releasing toxic gas. Replacement saved them from disaster and it is showing why regular furnace check-ups are important. When it comes to heat exchangers, overheating is like holding a hot potato, means you’ll get burned.

Overheating and Damage

High temperatures can harm the heat exchanger, leading to various issues. This can cause the furnace heat exchanger to overheat. Damage may affect its efficiency in heating your home. Uneven heating patterns and a drop in heating output might be the result. Excessive stress on the furnace may cause cracks, allowing hazardous gases to escape, which is hazardous to your health.

Air filters may become clogged or fouled, making it hard for the furnace to circulate air. A poorly maintained or installed heat exchanger may cause higher energy costs and lower quality air output.

Signs of Furnace Heat Exchanger Issues


In order to identify furnace heat exchanger issues with noise and water vapor, flue gas and combustion gases, and moisture and carbon monoxide levels, start by understanding how the heat exchanger works. 

The primary exchanger heats the air by transferring heat from the metal plates or coils, while the secondary exchanger extracts heat from the combustion gases. 

If you notice any strange noises, water vapor, or changes in gas color, this may indicate a problem with the exchanger. Similarly, high moisture or carbon monoxide levels are a sign that you need to tune up your heating system or contact a qualified HVAC technician to address any issues.

Noise and Water Vapor

A furnace with a faulty heat exchanger may produce odd sounds and extra water vapor. This could be a sign of a bigger issue. Heat exchangers are designed to transfer heat, while stopping carbon monoxide and other dangerous gases from entering your home.

Heat exchangers breaking down can lead to restricted airflow in the furnace. This causes pressure imbalances, creating strange noises. Cracked and worn components can create an accumulation of moisture inside the unit. This turns into water vapor that comes out of your vents.

It’s important to keep up with routine maintenance for your furnace. If you hear unusual sounds or water vapor, call a professional HVAC technician. They can inspect and fix any issues before they get worse and harm your family.

Flue Gas and Combustion Gases

Gases released during burning are a key sign of your furnace’s health. Carbon monoxide, oxygen, and other exhaust gases should be monitored often, to ensure proper and safe running.

Here is a breakdown of the gases, and what they mean:

ParameterHealthy RangeIndicator of Issues
Carbon Monoxide (CO)Below 100 ppmDamaged or Inefficient Heat Exchanger
Oxygen (O₂)2-4%Cracked or Malfunctioning Heat Exchanger
Top and Bottom Flue Temperature DifferenceLess than 75°FRestricted Airflow that can cause System Failure

Plus, if furnace parts are covered in soot, it could mean inefficient burning, or something wrong with the heat exchanger. If you see signs, call a professional.

Pro Tip: Regularly checking on flue gas parameters can save you money in the long-run. Finding moisture and carbon monoxide in your home? Not ideal.

Moisture and Carbon Monoxide Levels

The furnace is a must in cold months. But, problems can occur as time passes. An indicator of heat exchanger issues is an imbalance in ‘Air and Gas Flow’, which leads to high moisture and carbon monoxide levels.

Monitor carbon dioxide from the furnace. Use a hygrometer to measure humidity. Unhealthy air and damages to internal parts are possible. 

Below are winter humidity levels:

Inside:30-50%
When outside is 20ºF:35% RH
When outside is 10ºF:30% RH
When outside is 0ºF:25% RH
When outside is -10ºF:20% RH

You should watch for high moisture and CO2 levels. It’s important to keep living areas healthy.

Checking heat exchangers is critical. HVAC technicians have found that leaks from humidifiers and clogged coils increase contamination risks. Regular maintenance and monitoring is needed to keep the furnace running smoothly. This way you can save repair costs and extend the appliance’s lifespan.

Take good care of your furnace heat exchanger unless you want frozen pipes and icy showers.

Maintenance and Service for Furnace Heat Exchanger


To ensure the longevity of your furnace heat exchanger, maintenance and service are crucial. So, what can you do?

In order to keep your system running efficiently, you should schedule regular tune-ups and filter changes. If you encounter any common problems with your heating system or air conditioning, there are options for repair. However, it is highly recommended that you contact a qualified HVAC technician to do the job. 

Tune-Ups and Filter Changes

For optimal furnace heat exchanger functioning, routine maintenance and filter changes are essential. 

These actions protect against problems and boost efficiency.

  • Schedule Tune-Ups: Get your furnace heat exchanger regular tune-ups to extend its life and enhance its performance.
  • Replace Filters: Change filters to deter dust and debris build-up and ensure smooth running.
  • Clean Components: Regularly clean components such as burners, ignition systems, and ducts to decrease malfunction risks.

More benefits of proper maintenance include better air quality, lower energy costs, and a safer home environment.

For extra help, consider using a qualified heating contractor or HVAC technician for periodic maintenance checks. Their advice can help you maintain your unit and anticipate issues. In the end, sticking to regular maintenance keeps your furnace heat exchanger running for years to come. When your heating system stops working, it’s time to call in a professional.

Heating System and Air Conditioning Repair

Heating and cooling system repair services include maintenance for furnace heat exchangers. This upkeep lengthens its life, avoiding expensive repairs or replacements. Plus, it aids efficient operation, bringing down your energy bills.

It’s necessary to clean the exchangers regularly since a clogged one can cause carbon monoxide leaks, endangering your family’s well-being. Professionals check, scrub, and replace worn-out parts to keep it running.

Installing a carbon monoxide detector in the home is essential. It’s also smart to get an annual check-up from experts to detect and repair problems with boilers or fans.

To save even more energy, install a programmable thermostat to automatically set temperatures. Also, insulating ducts in attics or crawl spaces stops temperature loss in winter.

So, regular maintenance and service of furnace heat exchangers keeps your home safe and cuts energy expenses. By finding issues quickly, you avoid major fixes or replacements that can cause trouble and cost a lot later. For safety’s sake, it’s always best to call an HVAC technician than attempt the repair yourself.

Contacting a Qualified HVAC Technician

If your furnace heat exchanger needs maintenance or service, get help from a qualified HVAC technician. They are experienced and have the right tools for your furnace to work efficiently and safely. Provide them with detailed informations about your system and the issues you’re facing. Ask about their certifications, licenses, and insurance coverage to make sure they are credible.

Get routine maintenance on your furnace heat exchanger at least once a year. This prevents breakdowns. Common services include cleaning/replacing air filters, checking motors/blowers, adjusting belts/pulleys, tightening electrical connections, and testing controls.

Unqualified individuals for furnace service can cause hazards like carbon monoxide gas leaks, which can lead to death or serious health consequences. So, only consult licensed technicians who prioritize safety. Protect your family from the cold, not from a faulty furnace heat exchanger.

Importance of Furnace Heat Exchanger Safety


To ensure your safety and keep your furnace working efficiently, it’s essential to understand the significance of furnace heat exchanger safety. 

Carbon Monoxide Detectors

Carbon Monoxide Detection Systems are a must-have safety device. They detect carbon monoxide buildup in closed spaces, alerting you to potential poisoning. This can be fatal.

  • Placement: Install them outside sleeping areas, on each floor. Follow manufacturer instructions and legal requirements.
  • Maintenance: Test regularly with the test button. Replace batteries yearly or when notified.
  • Battery Life: Varying life span but usually between 4-7 years.

They not only detect CO from furnaces/HVAC systems, but also from other sources like gas stoves, water heaters, chimneys, and fireplaces.

One family installed a detector and got an unexpected alarm at midnight. Their furnace heat exchanger was cracked, emitting high levels of CO. Without the alarm, it would have been deadly. 

Following Manufacturer Guidelines

To get your furnace heat exchanger up and running safely, you must follow the manufacturer’s instructions. 

Here’s a three-step guide to help get you started:

  1. Read the manual – Check out the manual that came with your exchanger. Be sure to know all the parts before beginning.
  2. Assemble properly – Put together all components as instructed. Don’t miss any steps.
  3. Test it – After assembly, test for air leaks and other issues.

Remember, following these guidelines is key to avoiding physical harm and even death. Don’t skip or rush through the installation process

Regular Inspections and Safety Checks

For a furnace heat exchanger to work safely and efficiently, regular maintenance and safety procedures are absolutely essential

Here are five points to remember:

  • Have a professional inspection done annually, before winter.
  • Check for carbon monoxide detectors, gas leaks, and venting system.
  • Replace air filters regularly. This prevents dust and debris from accumulating.
  • Use high-quality air filters for clean air circulation without reducing airflow.
  • Take care of wear and tear with regular repair services.

Other tasks include inspecting the pilot light, blower wheel performance, thermostat calibration, fan control center operation, and ensuring proper installation techniques.

Conclusion


The furnace heat exchanger is key for your heating system. It transfers the heat from the combustion process to warm the air in your home. Over time, it can get cracks due to metal fatigue or corrosion. Soot and overheating can cause damage and be unsafe. To ensure that your furnace is efficient and safe, you should get regular maintenance from a qualified HVAC technician. They can tune up and clean out filters, vents, metal plates, and coils to reduce the risk of breakdowns, noise, and toxic gas leaks like carbon monoxide (CO). It would be smart to install carbon monoxide detectors too. If you think something is wrong with your furnace heat exchanger, such as cracks or moisture buildup, contact Oak Island Heating or White Mechanical. Don’t wait till it’s too late. A cracked heat exchanger can release dangerous fumes into your home, which could lead to health issues for you and your family.

About the author

Debarghya Roy: A heating systems author, Passionate about energy efficiency and sustainability, Sharing insights and empowering readers through informative blog articles.