Everything You Need to Know About Heat Exchangers

Heat exchangers might not be something you need to know about in everyday life, but when it comes time to service or upgrade your furnace or boiler, it can be useful to know a few basics about these systems.

Knowing about heat exchangers can help you decide whether it’s worthwhile to pay for maintenance on an older furnace or boiler, assist you in choosing a new heating system for your home, and make it easier for you to compare the warranty terms offered by different brands.

This guide will explain what heat exchangers are, how they work, why they’re important, and what new technologies are available, as well as cover important points you need to know to make informed decisions for your home and HVAC system.

What is a Heat Exchanger and How Does It Work?

In the simplest terms, the heat exchanger is the component inside your furnace or boiler that creates the heat that warms your home. Without a heat exchanger, your furnace wouldn’t be much more than an expensive metal box.

Here’s a slightly more in-depth explanation of how a furnace’s heat exchanger works:

When your thermostat registers that your home is too cold, it sends a message to the furnace to turn on.

The heat exchanger is connected to the burner at one end, and that’s where the combustion process begins. Inside the heat exchanger, gas combusts and creates heat. This heats the surface of the heat exchanger.

The furnace then brings in cool air from your home using the air return ducts. The blower then blows air across the surface of the heat exchanger, thereby heating the air. That heated air is then distributed throughout your house using the ductwork and vents.

At the other end of the heat exchanger, the system is connected to a flue that safely vents combustion by-products outside, keeping the air in your home clean and breathable.

Heat Exchangers Are Also Safety Devices

An important thing about a heat exchanger is that it doesn’t just produce heat—it also keeps the combustion process contained so that your home doesn’t fill with dangerous gasses like carbon monoxide.

This is one reason professional installation is so vital when you get a new furnace. If the furnace isn’t properly connected to the gas line and flue, then it could pose a serious threat to your family’s health and safety. This is also why regular furnace maintenance and inspections are necessary.

Proprietary Designs and Innovations

Over the years, HVAC and other manufacturers have worked hard to perfect the heat exchanger and come up with new and improved designs, especially for furnaces. When you go shopping for a new furnace, you might come across terms like clamshell, RPJ, and more.

Let’s have a look at these terms, and the new and proprietary designs that are available from some furnace brands:

• Clamshell: A clamshell heat exchanger is one that doesn’t rely on welds to keep the joints together. This increases longevity by reducing cracking or separating of the joints. Brands that use this design include Lennox, Comfortmaker, Tempstar, and Heil.
• RPJ: This stands for Rigid Press Joint, and it’s a type of clamshell heat exchanger. You can find this component with several furnace brands, including Heil, Tempstar, and Comfortmaker.
• Crimped: This is similar to the clamshell idea, so the joints are crimped together instead of welded to prevent damage from heat stress, improve airflow, and increase durability. This design is available with select Trane and Armstrong (EHX technology) furnaces.
• Turbulators: A turbulator is a device that causes irregular motion of a fluid. When you add a turbulator to a heat exchanger, like Napoleon’s Vortex, it disrupts airflow inside the heat exchanger and recovers more heat from flue gasses.
• Stainless Steel: Some manufacturers like Trane offer stainless steel heat exchangers which may be more durable and longer lasting than aluminium ones.

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The Benefits of a Secondary Heat Exchanger

When it’s time to upgrade your heating system, you’ll probably come across condensing furnaces or boilers. These are options you’ll want to consider because they’re more efficient and have less energy loss than traditional models.

Condensing furnaces and boilers have two heat exchangers. The primary heat exchanger works as described above, with combustion gasses being passed into the flue to be vented outside.

But in condensing boilers and furnaces, the combustion gasses instead pass into a secondary heat exchanger, where water vapour forms. This process releases heat, thereby heating the surface of the secondary heat exchanger, which is used to heat the air.

Secondary heat exchangers recover heat and energy that would otherwise be lost in a regular furnace or boiler, so condensing models are more efficient and can heat your home for less.

Common Heat Exchanger Problems and Symptoms

Heat exchangers are made of metal that’s constantly heating up and cooling down, so fatigue (weakening) from heat stress is one of the most common problems with these systems. Stress can cause cracks, joints to separate, and other failures.

Earlier, we talked about how heat exchangers function as safety devices, so you can see why a crack could be so dangerous. A cracked heat exchanger can allow exhaust gasses to escape into your home, potentially causing carbon monoxide poisoning and other problems.

The most obvious sign that there’s a problem with your heat exchanger is that your furnace or boiler stops working as it should. But other symptoms to look for include:

• The smell of gas (in that case, get your family out of the house and call your utility company or an expert HVAC technician)
• Cracks in the heat exchanger or furnace
• Soot buildup
• Rusty heat exchanger
• Pooled water on the floor

Repairing a Heat Exchanger Versus Buying a New Furnace or Boiler

Choosing between maintenance and upgrading a furnace or boiler can be a difficult decision, but luckily there are some simple rules to help you make the right one.

Rule #1: Replace Older Models

Heat exchangers tend to last between 10 and 20 years, so if your furnace or boiler is upward of 10 years, then you might be better off replacing it.

And when you do upgrade, you’ll get a more efficient unit with modern technology that will reduce your energy bills and make operation a breeze.

Rule #2: Repair a Warrantied Heat Exchanger

Heat exchanger warranties typically last anywhere between 10 years and the lifetime of the unit, so if the manufacturer is going to pay for the repair or component replacement, then you might as well take them up on the offer.

Rule #3: Upgrade When Repairs Get Too Pricey

Draw the line at 50 percent: if the cost of the repair will be more than 50 percent of what you’d pay to buy a new furnace or boiler, then don’t waste the money on the repair. A heat exchanger can cost well over $1,000 to repair or replace, and that could get you well on your way to a brand new furnace or boiler.

Rule #4: Replace Cracked Heat Exchangers

Once a heat exchanger cracks, it’s safer to replace it than repair it. Because of the cost of a new heat exchanger, you might be better off upgrading your entire heating system.

Common Warranty Terms for Heat Exchangers

extremely pricey. Repairing or replacing a heat exchanger is costly, so you’ll want to look for brands and models that are backed by long warranties.

The warranty coverage for a heat exchanger will depend on the manufacturer and what type of heating system you have:

Boilers: HVAC manufacturers typically warranty the heat exchangers in their boilers for 10 to 12 years.

Furnaces: Most brands warranty the heat exchangers in their furnaces for at least 20 years, and lifetime warranties are quickly becoming the norm, especially for the mid- and top-tier furnaces from most brands.

Another thing that’s becoming more common for furnaces is lifetime replacement warranties. With this type of warranty, the manufacturer will replace the entire furnace if the heat exchanger or another major component fails during the coverage period.

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