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, allows for the safe distribution of heated air throughout your home. Typically, homeowners find heat exchangers 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 example, look at a gas-powered forced air HVAC system. This is the most popular type of system used in homes today.
- 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.
- 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.
- 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. In these furnaces, the gases run through a second heat exchanger that 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 (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. 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. Things such as design, installation and maintenance can speed up the failure of a heat exchanger. For example, watch out for:
- Bad design and installation.
- Poor equipment design by the manufacturer.
- Improper maintenance.
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
Replacing a furnace heat exchanger requires a qualified HVAC professional. Due to safety concerns and possibly voiding the manufacturer’s warranty, you do not want to repair the furnace either. This isn’t a job that you want to DIY.
Although furnace heat exchanger repair remains an option, typically replacing the entire furnace provides a more cost effective option. Replacing a heat exchanger requires about 8-10 hours to dismantle the furnace and replace the heat exchanger. Rates vary for quality HVAC assistance, so the cost varies as well. Due to the estimated repair time, many homeowners replace the entire furnace when the heat exchanger dies.
The best person to help you evaluate your specific situation is a qualified HVAC professional.