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Furnace Heat Exchanger: An In-depth Look

Looking at the Heat Exchanger

First, let’s look at the term “furnace heat exchanger.” This term can be quite technical when you’re hearing it for the first time.

I know I felt confused and wondered what this term meant back when I first heard it.

However, by going over a few of its main uses and intentions, you will be able to understand what a heat exchanger is and does.

You may find that contractors use this word as a technical reference when referring to a furnace.

The fact is:

A heat exchanger is one of the most important parts of a furnace.

As you read through the article, you’ll be able to understand the complexity and fundamentals of what a heat exchanger does, how to maintain it and much more.

What is a Heat Exchanger?

heat exchanger for a home furnace

Example furnace heat exchanger from Goodman

To put it simply, the heat exchanger is what heats your air in the furnace before filling up the furnace plenum and distributing air from there.

Knowing a few things about your furnace and heat exchanger can help you next time a contractor goes out to your home for a repair or if you want to do a couple of maintenance tasks.

It can also be helpful if you want to take on the job or DIY repairs and installations. I, myself, have taken on a number of jobs around the house, which has saved me money.

Anyways, back to the topic at hand. The heat exchanger is mainly composed of a collection of tubes and coils.

These coils and tubes are looped throughout the system in a repeated fashion.

This lets the air flow freely through the tubes, which gives it time to heat up in the furnace.

Let’s break this down a bit.

First, the coils are an essential part of the furnace because they evaporate the refrigerant as it is absorbed and heated from the inside air.

It is also important to note that the shapes and sizes of these tubes may differ, depending on the furnace model.

How Does a Heat Exchanger Work?

The inner workings of the heat exchanger are simple.

They can be compared to a hot cup of coffee. At first, the cup of coffee can be too hot to drink.

However, by blowing on the coffee, you are essentially cooling it down and distributing the hot air away from the coffee.

Hopefully, this makes sense. If it doesn’t, don’t worry. Most people don’t grasp it right away.

All kidding aside, the heat exchanger works in a similar way.

The furnace uses a type of fuel to combust inside your furnace to create heat that is then distributed by the blower, or fan, inside your furnace.

This fan blows the hot air throughout your home as it is cooling down the heat exchanger at the same time.

In effect, it is “exchanging” heat for cooler air. You benefit by getting the displaced heat blowing throughout your home.

What to Do if Your Heat Exchanger Isn’t Working?

You’ll quickly notice if something is wrong with your furnace if it is not heating properly.

This can be due to many factors.

However, if the blower is working and air is coming out, then you may have a problem with your heat exchanger.

What to do?

Some things that you can look for can include vibration issues or exchanger leaks.

You may also notice a difference in your electric bill if your heater isn’t working properly.

Cool air may also start coming out of the furnace, which means you should run a leak test and see if your exchanger needs a repair. 

Depending on the issue, you may also need to consider an entire replacement of the heat exchanger.

However, if it’s something small, determining the problem can help to improve the performance of the heat exchanger.

It’s a good idea to note the problems as you begin your audit.

Most of the time, one symptom can lead to another problem, which leads to a chain reaction of issues until you find the underlying cause.

Here’s an example:

There can be air leakage coming from the exchanger.

Many times, flow distribution issues can be the problem and can lead to vibrations in the exchanger.

If you do not take care of this, it can lead to erosion of the exchangers and greater frequency of leaks.

Then what?

Within time, the costs can increase dramatically around maintaining your furnace.

The heat transfer can result in high energy consumption due to poor heat exchanges.

Although other parts of the tubes can’t provide enough heat, the fans and pumps may be able to compensate to give you the heat you need.

However, this will lead to mechanical failure sooner or later.

Here’s what else.

Fouling is another issue that can cause problems.

This kind of build-up can include crystallization, corrosion and sludge buildup.

You can usually wash and clean your filters on a regular basis to prevent any type of dirt or deposit settlement in your system.

Most importantly, a cracked heat exchanger can be extremely dangerous.

If you think that your heat exchanger is damaged in any way, it is always best to have a professional look at it.

Remember that the way a furnace works is by burning fuel or another type of material that can leak into the air, which includes carbon monoxide.

Maintenance is Important for Your Heat Exchanger

How to clean a heat exchanger

Knowing your heat exchanger before you begin to perform maintenance tasks is important.

Aside from the standard tube and shell heat exchangers, you may also find another type, which is the plate and frame exchanger.

Both these types can be cleaned and maintained in different ways, so it is important to know which type of heat exchanger you have in your home.

Here’s how:

One simple way to maintain your heat exchangers on a regular basis is to clean or replace your filters once a month, which depends on the model.

Another way is to clean the tubes themselves.

Although we’ll go more into detail about the process in a bit, the most important thing to remember is to turn off the power whenever you’re working on electrical devices.

This will also include your furnace and heat exchanger. 

Heat exchangers can use water and air to complete the process of heating your home.

Got hard water?

Another reason a heat exchanger can fail is due to hard water and excessive dirt.

The water can deposit calcium and other minerals that can form over time.

This will lead to an internal blockage of the tubes and overall failure of the system.

Repairing and Maintaining Your Heat Exchanger

Proper maintenance can prevent costly repairs.

I recommend doing this project on a weekend when you have more free time in case some things don’t work out.

Write things down

Talking from experience, I have always made notes or written the steps down on a piece of paper when it comes to working on a mechanical project.

This can help you remember where the parts go and what tools to use.

Rest assured that you should not leave out any parts when you’re putting the heat exchanger or furnace back together.

Let things cool down first

Once you have turned off the power from the circuit breaker, leave some time before you start working so that the heat exchanger can cool down.

This can prevent any accidents when working around the furnace.

If you don’t let the heat exchanger cool, striking the tubes or coils accidentally can cause a puncture, which can lead to hot steam coming out.

This is not good for several reasons!

Obviously this is an important safety tip to remember.

Protect your hands

Because you will be working around metal and sharp objects, remember to wear gloves as you start to work on the heat exchanger.

Where is my heat exchanger?

You can begin by removing the front panels of the furnace with a screwdriver.

You can find the heat exchanger behind these panels where you should see a collection of pipes and hoses.

At this point, always remember to note which hoses connect where because you will have to disconnect it.

You can use a small vacuum to clean out any dirt, dust and other types of debris from the exchanger.


Now, make sure to use water and soap to clean the tubes.

Using a damp cloth to do this would be a good idea. You can dry the tubes with a dry towel once you’re finished wiping them down with soap and water.

You can work freely around the exchanger by removing the tube fittings and hoses with a wrench or screwdriver.

Before you start cleaning the inside of the heat exchanger, mix fresh water with the heat exchanger cleaner to create a solution.

You can use a pipe brush to dip into the solution.

Using this pipe brush, clean the inside of the exchanger until you’ve removed all the dirty buildup.

The last cleaning step…

Finally, flush the heat exchanger with clean water.

It is ideal to let the exchanger air dry once you’re finished.

Complete the entire process by using a power washer filled with cleaner and water.

You can attach the hose to the intake tube of the exchanger and attach the other end of the hose to the bucket.

Simply turn the washer on and flush the tubes with the treated water.

Once you’ve cleaned it out with the treated water, use fresh water to finish flushing the tubes.

This completes the process of washing and cleaning your heat exchanger.

Finally, use the notes as a reference so that you can attach the exchanger back in its place.

Make sure to replace the panels and covers before turning on the power.

FAQs to Better Understand Your Furance Heat Exchanger

Q: Do all furnaces have a heat exchanger?

A: Yes, all furnaces need a heat exchanger to function properly.

Q: Is there a difference in heat exchangers when it comes to gas or oil furnaces?

A: No, the heat exchanger will work the same way and with the same results. The make and model of the furnace won’t matter.

Q: Are heat exchangers only used for heating purposes?

A: No, a heat exchanger can be used for both cooling and heating.

Q: Are heat exchangers dangerous?

A: As with any home appliance, you want to take great care of it so that you won’t have to worry about leaks.

Maintenance and timely repairs are important to prevent any accidents regarding a heat exchanger or furnace.

Q: Do you need to turn off the electricity when working on a heat exchanger?

A: Yes, it is important to turn off all power whenever you’re working on a heat exchanger.

You can turn off the power by flipping the switch to the off position at the circuit breaker.      

Q: Can you only use water to flush the tubes?

A: Although using water can help to clean the tubes, using a cleaning solution for your heat exchanger does wonders in removing dirt, debris and sludge buildup.

Q: How does the heat exchanger work?

A: The heat exchanger works by creating an intense heat inside while a fan blows the hot air throughout the system. 

Final Summary of the Heat Exchanger

In the end, the heat exchanger is an essential part to any furnace and its inner workings.

Whether you want to maintain, repair or even install a heat exchanger, it is important that you research this device before you get to work.

By doing this, you will be able to get the results you want.

You won’t have to deal with any malfunctions or accidents.

Prevention is key…

The best way to prevent breakdowns on your heat exchanger is to clean it on a regular basis or before the cold temperatures arrive at your home.

This will optimize the heat exchanger so that you’re prepared for those freezing temps.

Remember to write down the diagram of the heat exchanger so that you can reattach it once you’re finished repairing or cleaning it.

If you are not certain about an issue regarding your furnace heat exchanger, it is always best to call the professionals…and you can stay warm!

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