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Common Problems with Furnace Heat Exchangers


Over time as your furnace heat exchanger works to keep your home warm during the cold season, it can experience some operational issues and show symptoms of a bad heat exchanger. This can result in needing your heat exchanger or furnace replaced or repaired.

Here we will let you know everything about the signs of a broken heat exchanger and how to fix them.

How Does A Furnace Heat Exchanger Work?

That familiar sound of your furnace kicking on is how you can tell your furnace heat exchanger is working. This happens when the thermostat activates if the temperature in your home goes below the set heat temperature.

This will cause gas to flow into the chamber of the heat exchanger and ignite. This combustible gas will leave the furnace through an outdoor vent pipe. The ignition will cause the heat exchanger’s exterior walls to warm up. Then the blower motor will activate and begin collecting cold air from every space in your home. This air will flow to the heat exchanger through a return air duct.


Once the furnace has been fed the cold air the walls of the furnace heat exchanger will increase the temperature of the air. It will then be distributed to your home by way of a series of air ducts. Once your home reaches the set temperature on the thermostat it will send a signal to the furnace to shut down.

What Are The Signs Of A Broken Heat Exchanger?

There are a variety of different signs that will help you to see that your heat exchanger is having problems. We’ve compiled a list of common signs that you have a broken heat exchanger.


Water Around The Furnace

Condensation on the outside of your furnace is a normal cause of seeing puddles form at the base of your furnace. However, if there is no condensation present and the furnace is dry on the outside, there may be a clog in your internal drain system. You will need to inspect this area for clogs. You’ll also want to check that the exchanger and humidifier are not damaged.

Producing Formaldehyde Smells

If you notice a strong chemical smell in your air, your furnace may be putting out formaldehyde fumes. Call a technician as soon as you can for an inspection. This can be dangerous fumes for your pets and family to inhale. A licensed professional will be able to resolve the problem your gas furnace heat exchanger is having and make a quick replacement.

Cracks & Corrosion on the Exterior

When your furnace begins to show signs of deterioration such as cracks and corrosion, they may be normal. Some minor damage to the access panel is okay. But if your heat exchanger has a crack or signs of disintegration, present carbon monoxide can leak from your furnace.

Having a technician do an inspection once a year that looks for any issues present with its components such as the flame sensor, gas valve, thermocouple, or electric igniter is very important. Having these inspections can prevent many issues.

Dirty Heat Exchanger & Furnace Interior

Seeing dirt collected in your heat exchanger and furnace interior is a common sign of a bigger issue. Your exchanger may be cracked, the gas burner may be tilted, or another problem might be occurring with your heat exchanger. A professional can inspect this and determine what the best solution is.

What Causes Cracks In Heat Exchangers?


There are a few reasons for cracks in your heat exchangers which will result in your furnace needing a replaced exchanger. The reasons for cracks can include:

  • Small Furnace
  • Too large of a furnace
  • Airflow is weak or bad
  • Not enough combustion
  • Old furnace

How Much Does It Cost To Replace A Heat Exchanger?

Replacing a heat exchanger in your gas furnace is not a cheap project but it is necessary for your furnace to put out the correct temperature of air. Installing a new heat exchanger will cost you about $2,000 to $3,500. However, in some cases replacing your furnace may be the better option.

Should You Replace Your Heat Exchanger or Furnace?

While replacing your heat exchanger seems like the cheaper option, replacing your furnace may be the better move. It does cost more upfront but is a great investment down the line especially if your unit is more than 10 years old, is having issues heating your home, or the warranty for parts and labor has lapsed. Replacing your whole unit can cost $4,500 to $12,000 – which depends on who you hire to complete the job.

The HELP team has knowledgeable professionals that can help you decide if you should replace your heat exchanger or furnace. They are also experienced in heat exchanger and furnace installation and repair. Give us a call today to schedule an inspection or to set up an installation!

Posted in: Heating

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