What Is A Furnace Heat Exchanger? How a Furnace Heat Exchanger Works, Common Problems, Costs and More

How a furnace heat exchanger keeps your home comfortable

What Is A Furnace Heat Exchanger? How a Furnace Heat Exchanger Works, Common Problems, Costs and More

(Last Updated On: June 29, 2017)

Definition of Furnace Heat Exchanger

A furnace heat exchanger is the part of your furnace that is responsible for keeping your breathing air and the combustion process separate. This is absolutely essential to prevent carbon monoxide poisoning. A furnace heat exchanger begins at the burner assembly of the furnace, and goes to the spot where the chimney vent connects with the furnace. This passageway, combined with a metal chamber, is what allows heated air to be safely distributed throughout your home. Heat exchangers can be found within furnaces, refrigerators, vehicles, and even some pools.

How A Furnace Heat Exchanger Works

A furnace heat exchanger works by literally exchanging (or transferring) the heat created in the combustion chamber to the exterior of the unit, where it is then blown through the ductwork throughout the house. It does this in three basic steps. For our example we are looking at a gas-powered forced air HVAC system, as this is the most popular type of system used in homes today.

  1. First, the furnace will call for heat, which begins the combustion process. The hot combustion gases enter into the chamber of the heat exchanger, where they heat up the metal walls.
  2. The return air ducts then draw cold air from within the home to blow along the outside of the heat exchanger. The air is warmed as it blows along the heated walls of the exchanger, before being sent back through the ducts to the various rooms of your home. Through this process, combustion gases and breathing air are kept separate.
  3. The gases created during the combustion process are then blown out of the heat exchanger and through a vent outside of the home. High-efficiency condensing furnaces work a little bit differently, as the gases are run through a second heat exchanger which draws additional heat for use in the home.

Benefits of a Furnace Heat Exchanger

The main benefit of a properly functioning furnace heat exchanger is that it helps to keep occupants of the home safe from combustion byproducts. If dangerous flue gases were to mix with the breathing air in the home, it could be a potentially fatal disaster. This is why it is so important (and sometimes the law) to have a carbon monoxide detector installed in any home with a fuel-burning appliance. For this reason, it’s also important to maintain your furnace’s heat exchanger.

Problems With Heat Exchangers

A common problem with furnace heat exchangers is that they will fail at some point. This is the result of what’s known as ‘metal fatigue’. This occurs as the result of the metal walls constantly being heated (expanded) and cooled (contracted). It is the same effect as bending a paperclip back and forth — it will eventually break the metal. As such, all homeowners should be prepared to replace their furnace heat exchanger at some point during the life of their furnace.

Most furnace heat exchangers should last between 10 and 20 years, but there are a number of factors that can affect the wear and tear. Poor initial system design and installation, poor equipment design by the manufacturer, and poor maintenance can all speed up the failure of a heat exchanger. A qualified HVAC professional should inspect your furnace’s heat exchanger for cracks or holes using an infrared video inspection system as part of your annual HVAC maintenance. If your heat exchanger is faulty, you’ll need to either replace it, or the entire furnace.

Cost of A Furnace Heat Exchanger

If your furnace heat exchanger needs to be replaced, you’ll need to call in a qualified HVAC professional, who can assess the situation and perform the work. This isn’t a job that you want to DIY. You also should never try to repair a heat exchanger, as their safety cannot be guaranteed, and it may even void the manufacturer’s warranty on your furnace.

Replacing a heat exchanger costs around $1500 all in, with the most expensive aspect being the labor. It takes about 8-10 hours to dismantle the furnace and replace the heat exchanger. With varying rates for quality HVAC assistance and a lengthy time to complete the project, you can see why it is appealing to simply replace the entire furnace when the heat exchanger dies.

While the heat exchanger of many furnaces can be replaced, it is often more cost effective to replace the entire furnace after you factor in parts and labor. The best person to help you evaluate your specific situation is a qualified HVAC professional.

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