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Cozy winter nights are around the corner and it’s time to make sure that your furnace is in proper condition! The largest component of your furnace is a heat exchanger

The heat exchanger in a furnace is a device that does exactly what the name states – it exchanges heat (or transfers thermal energy). It also doesn’t let combustion gases mix with the air that we breathe. The heat exchanger is the main component of the furnace that is the closest to the burners and which is responsible for creating warm air in our houses.

In gas furnaces, natural gas begins the combustion process and starts heating up the heat exchanger. The combustion by-product (or exhaust) travels through the coil-like heat exchanger and warms up the air outside of it.

The blower fan, in its turn, blows the air through the heat exchanger and pushes it through the ducts to the various parts of your home. The exhaust and carbon monoxide gets released outside through the flue vent.

The heat exchanger on the gas furnace

Every gas furnace has at least one heat exchanger. The purpose of the secondary heat exchanger is to turn heated gasses into the water, and it is commonly found in high-efficiency models.

The primary heat exchanger in a furnace comes in a form of a tube or a clamshell. Clamshell is a little bit outdated model, that can be found in older furnaces:

In the newer furnaces, you will highly likely to find a heat exchanger made out of tubes. The larger number of tubes, the better the heating potential:

A secondary heat exchanger commonly has fins, and its main job is to complete the cycle of turning exhaust gases into the water:

The heat exchanger is usually located behind the panel and out of sight. Here is a nice diagram of a gas furnace from Goodman:

When the technician tells you that something is wrong with your heat exchanger, you can easily ask for some kind of proof in form of a picture or an experiment like this:

How heat exchanger works

When your thermostat gets to a certain preset temperature, it triggers gas burners that will start heating up your heat exchanger. As the blower gets turned on, it starts blowing air across the hot heat exchanger and this is how air gets warm.

After the hot air is no longer needed, the cooling down process of the heat exchanger takes place. This means that the tubes of the furnace expand and shrink to normal size in just one cycle.

Cracked heat exchanger

As time goes by, the process of expansion and contraction can lead to cracks in a heat exchanger. Natural gas byproducts, such as carbon dioxide or carbon monoxide, will exit your heat exchanger through those cracks, and the air that you breathe will not be safe anymore.

If you have a problem with a cracked heat exchanger, the first thing you can do is to check your warranty. Typically warranties on heat exchangers are separate from warranty on the furnace itself.

How heat exchanger is made

The primary heat exchanger is generally made out of aluminized steel because it transfers heat faster than stainless steel. The second heat exchanger is generally made out of stainless steel.

Now, let’s take a look at what heat exchanges look like when disassembled:

Heat exchanger life expectancy

Heat exchangers have a quite durable construction with life expectancy somewhere between 10 to 20 years. If there has been no maintenance done or there were some mistakes in installation, the life expectancy of the heat exchanger will be significantly lower.

Some furnaces now have a lifetime warranty due to better materials used and more advanced technology. Some furnaces will fail a lot sooner than 10 years due to poor design and cheap materials used.

Here is a good explanation:

The biggest problem with heat exchanges in older furnaces is that you really never know when there is a crack, and you have toxic gasses coming into your living area. Newer furnaces have more safety features that you can rely on and if there is something wrong with your furnace, it will automatically shut down (in some cases only for few hours).

It is always a good idea to have a professional checkup before resetting your furnace.

Attention! This article is for informational purposes ONLY and is NOT a replacement for a professional advice! You will need to visit school's website for details and updates, as well as consult your local HVAC specialist for appropriate solution to your problem.


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