Today I would like to go over the topic of cracked heat exchangers.

A heat exchanger is a piece of equipment that allows efficient transfer of heat between 2 mediums, in our case, air, without allowing them to mix.

In your gas furnace a heat exchangers purpose is to transfer heat from the gas flame into your home without letting any of the exhaust fumes in.

Here is an example
Not only does this prevent smelly fumes from coming into your home, it also protects you and your family from potentially deadly fire risks and carbon monoxide poising.

Carbon Monoxide (CO) is a colorless, odorless, tasteless gas, that is very hard for people to detect. But when people or pets are exposed to this deadly gas, it gets into the bloodstream and bonds with the hemoglobin in our blood, rendering it useless. Hemoglobin is the compound found in blood that carries oxygen to our brain and other vital organs. Here is an excerpt from wikipedia on carbon monoxide. “Symptoms of mild acute poisoning include lightheadedness, confusion, headaches, vertigo, and flu-like effects; larger exposures can lead to significant toxicity of the central nervous system and heart, and even death. Following acute poisoning, long-term sequelae often occur. Carbon monoxide can also have severe effects on the fetus of a pregnant woman. Chronic exposure to low levels of carbon monoxide can lead to depression, confusion, and memory loss”

Carbon monoxide poisoning can occur when the heat exchangers in your furnace are compromised. several things can cause heat exchangers to fail. The leading cause is the repetitive heat and cool cycles of the furnace. Over years of heating up and, and in turn, expanding, then cooling down, and shrinking, the metal heat exchangers. They eventually have enough internal stress to begin to crack. Obviously this heating and cooling cycle is what your furnace does and its normal. So how do you protect yourself? Well we recommend a yearly maintenance on your furnace. During a maintenance your heating contractor will verify the competence of your heat exchangers in the process of completing the maintenance. Most manufacturers require you to have a maintenance performed on your equipment at least every 2 years to uphold the factory warranty.

Overheating the furnace can accelerate this process. The causes for over heating usually are either closed heating vents (you never want to completely close more than 1 or 2 heating registers), or a dirty filter. Filters need to be changed at least every 3 months. You can stock up on filters in our online store found HERE.

Heat exchangers can also fail due to rust or defective parts.

Here is an example of how CO poisoning can occur

Failed heat exchangers can also pose a serious fire risk. This risk comes when the pressure on the outside of the heat exchanger exceeds the pressure inside, and an opening such as a crack or rust spot allows air to blow into the heat exchangers. What happens in this case is instead of the flame heading through the heat exchangers and up the exhaust, it get pushed backward through the heat exchanger and goes into the furnace. most newer furnaces have fail-safes in place to turn off the gas if a heat sensor in the furnace is tripped. However not all furnaces have this fail-safe. Assuming you do, do you trust the fail-safe will activate before any of the flammable wires, insulation, plastic, or gas lines catch fire?

So now you’ve had your furnace checked out and the tech found a crack in your heat exchanger. Now what?
Well, you have a few options. Though using your furnace in its current state is not one of them. The technician will have turned off gas and power to your furnace to ensure your safety. If the furnace is less than ten years old, odds are the exchangers can simply be replaced. Many of them are still under warranty in the first ten years and parts are typically available. However most warranties don’t cover the labor, and since changing heat exchangers requires completely disassembling your furnace, you can expect to pay for around 4 hours labor. If your furnace is more then ten years old it is usually recommended that you replace it in the event of heat exchangers being cracked. This is for a couple of reasons, the first is parts availability. Odds are the manufacturer is not making parts for furnaces more than ten years old, so finding replacements can be difficult. Another reason is cost. Most warranties are for ten years, after that point the cost of expensive heat exchangers coupled with several hours labor, rivals the cost of a new furnace. And once you pay all that money the rest of your furnace is still over ten years old and likely wont last much longer. The final option is to replace the furnace. This may not be as drastic as it sounds though. Pilchuck Heating offers highly competitive prices on some of the finest furnaces in the U.S. Some as low as 1750 installed! for a big name brand. Even lower for some of the second tier equipment. all installs even come with a brand new thermostat. Pilchuck Heating Also offers a 10 year parts and LABOR warranty on most new furnaces, and a 20 year minimum warranty on heat exchangers, many with LIFETIME heat exchanger warranties.

Here are some examples of cracked heat exchangers